Glossary Portney & Watkins Flashcards
regression line
The straight line that is drawn on a scatter plot for bivariate data from the regression equation, summarizing the relationship between variables.
sampling error
The difference between an observed statistic from a sample and the population parameter.
analysis of covariance (ANCOVA)
Statistical procedure used to compare two or more treatment groups while controlling for the effect of one or more confounding variables (called covariates).
positive predictive value
Estimate of the likelihood that a person who tests positive actually has the disease.
curvilinear relationship
The relationship between two variables that does not follow a linear proportional relationship.
phi coefficient
A nonparametric correlation statistic for estimating the relationship between two dichotomous variables.
Type II error
An incorrect decision to accept the null hypothesis, concluding that no relationship exists when in fact it does.
z-score
The number of standard deviations that a given value is above or below the mean of the distribution; also called a standardized score.
stratification
The grouping of individuals in a population into homogeneous groups on some characteristic prior to sampling.
sXhat
standard error of the mean
The standard deviation of ta distribution of sample means; an estimate of the population standard deviation
audit trail
Comprehensive process of documenting interpretation of qualitative data.
epidemiology
Study of the distribution of disease in relation to person, place and time, and measures of risk associated with exposures to disease.
nondirectional hypothesis
A research hypothesis (or alternative hypothesis) that does not indicate the expected direction of the relationship between variables.
target population
The larger population to which results of a study will be generalized.
grand mean
The mean of all scores across groups in an analysis of variance.
longitudinal study
A study designed to collect data over time, usually for the purpose of describing developmental changes in a particular group.
Newman-Keuls (NK) multiple comparison test
Amultiple comparison procedure, used following a significant analysis of variance. Also called the Student-Newman-Keuls (SNK) test.
nominal scale
Level of measurement for classification variables; assignment of “values” based on mutually exclusive and exhaustive categories with no inherent rank order.
Q-sort
An analytic technique used to characterize attitudes, opinions, or judgments of individuals through a process of comparative rank ordering.
treatment threshold
In clinical decision making, the point at which a decision is reached to treat the patient without first performing a diagnostic test.
Wilcoxon signed-ranks test (T)
A nonparametric statistical procedure, comparing two correlated samples (repeated measures); analogous to the paired t-test.
z distribution
The standardized normal distribution, with a mean of 0 and a standard deviation of 1.
Bayes’ theorem
The calculation of the probability of one event based on the probability of another event; used to estimate posterior (posttest) probabilities based on prior (pretest) probabilities of a diagnostic outcome.
degrees of freedom (df)
Statistical concept indicating the number of values within a distribution ntat are free to vary, given restrictions on the data set; usualy n-1. For analysis of variance, dfe = error degrees of freedom; dfb = between groupus degrees of freedom; dft = total degrees of freedom
σ
Standard deviation of a population
σ2 is the population variance
variance
s2
a measure of variability in a distribution, equal to the square of the standard deviation
factor analysis
An exploratory multivariate statistical technique used to examine the structure within a large set of variables and to determine the underlying dimensions that exist within that set of variables.
s
standard deviation (s) A descriptive statistic reflecting the variability or dispersion of scores around the mean.
standard error of the mean
The standard deviation of a distribution of sample means; an estimate of the population standard deviation.
systematic review
Review of a clearly formulated question that uses systematic and explicit methods to identify, select and critically appraise relevant research.
convergent validity
An approach in construct validation, assessing the degree to which two different instruments or methods are able to measure the same construct.
eigen value
A measure of the proportion of the total variance accounted for by a factor in a factor analysis.
experimental event rate (EER)
The number of subjects in the experimental or treatment group who develop the outcome of interest.
split middle line
In single-case research, a line used to separate data points within one phase into two equal halves, reflecting the trend of the data within that phase. (See celeration line.)
backward selection
A process used in stepwise multiple regression that enters all independent variables into the equation, and then removes nonsignificant variables in successive steps, until all remaining variables are significant.
recall bias
The possible inaccuracy of recalling medical history or previous exposures; of particular concern in retrospective studies.
scale of measurement
same as level of measurement
purposive sample
A nonprobability sample in which subjects are specifically selected by the researcher on the basis of subjective judgment that they will be the most representative.
single-blind study
An experiment in which either the investigator or the subject is kept ignorant of group assignment, but not both.
statistical conclusion validity
The validity of conclusions drawn from statistical analyses, based on the proper application of statistical tests and principles.
known groups method
A technique for construct validation, in which validity is determined by the degree to which an instrument can demonstrate different scores for groups known to vary on the variable being measured.
ordinal scale
Level of measurement in which scores are ranks.
box plot
Also called box and whisker plot. A graphic display of a distribution, showing the median, 25th and 75th percentiles, and highest and lowest scores.
Guttman scale
same as cumulative scale?
publication bias
Tendency for researchers and editors to treat positive experimental results (finding an effect) differently from negative or inconclusive results (finding no effect), often with a preference for publication of positive findings.
bimodal distribution
A distribution having two modes.
reactive measurement
A measurement that distorts the variable being measured, either by the subject’s awareness of being measured or by influence of the measurement process.
posttest-only design
An experimental design in which only one measurement is taken following treatment.
line of best fit
The regression line, representing the relationship between two variables, usually plotted on a scatter diagram.
random selection
same as random sampling. Probability method of selecting subjects for a sample, where every subject in the population has an equal chance of being chosen.
testing effect
The effect that occurs when a test itself is responsible for observed changes in the measured variable.
true positive
A test result that is positive for those who do have the disease or condition of interest.
single-factor design
An experimental design involving one independent variable.
sum of squares
SS
A measure of variability in a set of data, equal to the sum of squared deviation scores for a distribution: Σ(X-Xhat)2
The numerator in the formula for variance
frequency distribution
A list of values that occur in a distribution, with a count of the number of times each value occurs.
factor
- A variable. 2. A set of interrelated variables in a factor analysis.
adjusted means
Means that have been adjusted based on the value of a covariate in an analysis of covariance.
standard error of the mean
sXhat
The standard deviation of ta distribution of sample means; an estimate of the population standard deviation
internal validity
The degree to which the relationship between the independent and dependent variables is free from the effects of extraneous factors.
partial correlation
A statistical technique for establishing the correlation between two variables, with the effect of a third variable removed; also called a first-order correlation.
prospective study
A study designed to collect data following development of the research question.
sensitivity analysis
A procedure in decision making to determine how decisions change as values are systematically varied.
two-way design
An experimental or quasi-experimental study that involves two independent variables.
paired t-test
A parametric test for comparing two means for correlated samples or repeated measures; also called a correlated t-test.
specificity
A measure of validity of a screening procedure, based on the probability that someone who does not have a disease will test negative.
informed consent
An ethical principle that requires obtaining the consent of the individual to participate in a study based on full prior disclosure of risks and benefits.
df
degrees of freedom. Statistical concept indicating the number of values within a distribution ntat are free to vary, given restrictions on the data set; usualy n-1. For analysis of variance, dfe = error degrees of freedom; dfb = between groupus degrees of freedom; dft = total degrees of freedom
r
Pearson product-moment coefficient of correlation (r) A parametric statistical technique for determining the relationship between two variables.
facets
In generalizability theory, specific conditions under which reliability of a measurement can be generalized
one-tailed test
A statistical test based on a directional alternative hypothesis, in which critical values are obtained for only one tail of a distribution.
between subjects design
An experimental design that is based on comparison between independent groups.
MDD
minimal detectable difference (MDD) That amount of change in a variable that must be achieved to reflect a true difference; the smallest amount of change that passes the threshold of error. Also called minimal detectable change (MDC).
alpha coefficient
same as cronbach’s alpha
consecutive sampling
A form of nonprobability sampling, where subjects are recruited as they become available.
SnNout
When a test has high sensitivity, a negative test rules out the diagnosis.
incidence
The proportion of people who develop a given disease or condition within a specified time period.
skewed distribution
A distribution of scores that is asymmetrical, with more scores to one extreme.
agreement
same as percent agreement
false positive
A test result that is positive in a person who does not have the disease or condition of interest.
interrupted time-series design
A design involving a series of measurements over time, interrupted by one or more treatment occasions.
cross-sectional study
A study based on observations of different age or developmental groups at one point in time, providing the basis for inferring trends over time.
SEE
Standard error of the estimate: In regression analysis, an estimate of prediction accuracy; a measure of the spread of scores around the regression line.
on-protocol analysis
Analysis of data in an experiment based only on subjects who completed the study according to assigned groups. Also called completer analysis or on-treatment analysis.
double-blind study
An experiment in which both the investigator and the subject are kept ignorant of group assignment.
standardized score
see z-score
risk factor
A characteristic or exposure that potentially increases the likelihood of having a disease or condition.
snowball sampling
A nonprobability sampling method in which subjects are successively recruited by referrals from other subjects.
instrument all measure the same trait
Typically measured using Cronbach’s alpha.
logrank test
A statistical procedure for comparing two survival curves when censored observations are present.
triangulation
The use of multiple methods to document phenomena.
naturalistic inquiry
Qualitative observation and interaction with subjects in their own natural environment.
stepwise regression
An approach to multiple regression that involves a sequential process of selecting variables for inclusion in the prediction equation.
alternate forms reliability
Reliability of two equivalent forms of a measuring instrument.
prevalence
The number of existing cases of a disease or condition at a given point in time, expressed as a proportion of the total population at risk.
case-control study
A design in analytic epidemiology in which the investigator selects subjects on the basis of their having or not having a particular disease and then determines their previous exposure.
hazard function
The probability that a subject will achieve a specific outcome in a certain time interval.
SS
sum of squares
A measure of variability in a set of data, equal to the sum of squared deviation scores for a distribution: Σ(X-Xhat)2
The numerator in the formula for variance
historical controls
Subjects from previous research studies that serve as controls for experimental subjects in a subsequent study.
ROC curve
Receiver operating characteristic curve
standard error of the estimate (SEE)
In regression analysis, an estimate of prediction accuracy; a measure of the spread of scores around the regression line.
likelihood ratio
In diagnostic testing, the ratio indicating the usefulness of the test for ruling in or ruling out a condition. (See negative likelihood ratio and positive likelihood ratio.)
dfe
For analysis of variance,
= error degrees of freedom
natural history
Longitudinal study of a disease or disorder, demonstrating the typical progress of the condition.
single-subject design
An experimental design based on time-series data from one or more subjects, with data compared across baseline and intervention phases. Also called single-case designs.
weighted kappa
An estimate of percentage agreement, corrected for chance, based on weights reflecting levels of seriousness of disagreements.
goodness of fit test
Use of chi square to determine if an observed distribution of categorical variables fits a given theoretical distribution.
quartile (Q)
Three quartiles divide a distribution of ranked data into four equal groups, each containing 25 percent of the scores.
sign test
A nonparametric statistical procedure for comparing two correlated samples, based on comparison of positive or negative outcomes; analogous to the paired t-test.
true negative
A test result that is negative for those who do not have the disease or condition of interest.
factorial design
An experimental design involving two or more independent variables, allowing for the interpretation of main effects and interaction effects.
histogram
A bar graph of a frequency distribution.
residual
Y - Yhat
In regression analysis, the difference between the value of the dependent variable predicted by the regression equation and the actual value
ratio scale
The highest level of measurement, in which there are equal intervals between score units and a true zero point.
change score
Difference between two measurements taken at different times, typically between pretest and posttest or followup. Also called a gain score.
coefficient of determination (r2)
Coefficient representing the amount of variance in one variable (Y) that can be explained (accounted for) by a second variable (X).
generalizability
- The quality of research that justifies inference of outcomes to groups or situations other than those directly involved in the investigation. 2. The concept of reliability theory in which measurement error is viewed as multidimensional and must be interpreted under specific measurement conditions.
repeated measure (repeated factor)
An independent variable for which subjects act as their own control; that is, all subjects are exposed to all levels of the variable. Also called a within subjects factor.
Pearson product-moment coefficient of correlation (r)
A parametric statistical technique for determining the relationship between two variables.
transformation
Mathematical conversion of a distribution to a different scale by a constant (such as square root or log) to change the shape or variance characteristics of the distribution.
two-way analysis of variance
An analysis of variance with two independent variables.
s2
variance
a measure of variability in a distribution, equal to the square of the standard deviation
attribute variable
An independent variable with levels that cannot be manipulated or assigned by the researcher, but that represent subject characteristics (such as age and sex).
MCID
minimal clinically important difference (MCID) The smallest difference in a measured variable that signifies an important rather than trivial difference in the patient’s condition. The smallest difference a patient or clinician would perceive as beneficial, and that would result in a change in the management of the patient. Also called minimal clinically important change (MCIC) or minimally important change (MIC).
phi coefficient
rphi
A nonparametric correlation statistic for estimating the relationship a dichotomy and a continuous variable on the interval or ratio scale
norm referencing
Interpretation of a score based on its value relative to a standard or “normal” score.
point biserial correlation
ppb
A correlation statistic for estimating the relationship between a dichotomy and a continuous variable on the interval or ratio scale
continuous variable
A quantitative variable that can theoretically take on values along a continuum.
evidence-based practice
The application of clinical decision making for patient management based on research evidence, clinical expertise, patient values and preferences and clinical circumstances.
interquartile range
The difference between the first and third quartiles in a distribution, often expressed graphically in a boxplot.
limits of agreement
Index of reliability between alternate forms of an instrument.
LR -
negative likelihood ratio
A ratio that indicates how much the odds of a disease are decreased if a diagnostic test is netagive
Equals specificity/(1-sensitivity)
semantic differential
A technique used to measure attitudes by asking respondents to rate concepts on a 7-point scale which represents a continuum across two extremes.
common cause variation
Fluctuation in response resulting in random and expected variation in performance.
one-way design
An experimental or quasi-experimental design that involves one independent variable.
sampling distribution
A theoretical frequency distribution of a statistic, based on the value of the statistic over an infinite number of samples.
inductive reasoning
The logical process of developing generalizations based on specific observations or facts.
methodological research
Research designed to develop or refine procedures or instruments for measuring variables, generally focusing on reliability and validity.
Delphi survey
Survey method whereby decisions on items are based on consensus of a panel.
PV -
negative predictive value
In diagnostic testing, the proportion of subjects who are correctly identified as not having the condition of interest
randomized controlled trial (RCT)
An experimental study in which a clinical treatment is compared with a control condition, where subjects are randomly assigned to groups. Also called a randomized clinical trial.
counterbalancing
Systematic alternation of the order of treatment conditions, to avoid order effects in a repeated measures design.
variable
A characteristic that can be manipulated or observed and that can take on different values, either quantitatively or qualitatively.
logistic regression
Multiple regression procedure where the dependent variable is a dichotomous outcome; predicts odds associated with presence or absence of the dependent variable based on the independent variables.
SRM
standardized response mean
Tukey’s honestly significant difference (HSD)
A multiple comparison test for comparing multiple means following a significant analysis of variance.
regression analysis
In a regression equation, the weight (b) assigned to the independent variable; the slope of the regression line.
rphi
phi coefficient
A nonparametric correlation statistic for estimating the relationship a dichotomy and a continuous variable on the interval or ratio scale
dummy variable (coding)
In regression procedures, the assignment of codes to a nominal variable, reflecting the presence or absence of certain traits.
Postitive predictive value
PV +
Estimate of the likelihood that a person who tests positive actually has the disease
negative predictive value
PV -
In diagnostic testing, the proportion of subjects who are correctly identified as not having the condition of interest
level
- The “value” or classification of an independent variable. 2. In single-case research, the magnitude of the target behavior; changes in level are associated with differences in magnitude between the end of one phase and the beginning of the following phase.
r2
coefficient of determination: Coefficient representing the amount of variance in one variable (Y) that can be explained (accounted for) by a second variable (X).
point estimate
A single sample statistic that serves as an estimate of a population parameter.
standard error of measurement (SEM)
A reliability measure of response stability, estimating the standard error in a set of repeated scores.
autocorrelation
Correlation of consecutive data points in a time series design.
primary source
Reference source that represents the original document by the original author.
vital statistics
Mortality and morbidity rates.
confounding variable
A variable that is more likely to be present in one group of subjects than another, and that is related to the outcome of interest, thereby potentially “confounding” interpretation of the outcome.
efficacy
Benefit of an intervention as tested under controlled experimental conditions, usually with a control group in a randomized controlled trial.
independent factor
An independent variable in which the levels represent independent groups of subjects.
stopping rule
In a sequential clinical trial, the threshold for stopping a study based on crossing a boundary that indicates a difference or no difference between treatments.
critical value
The value of a test statistic that must be exceeded for the null hypothesis to be rejected; the value of a statistic that separates the critical region; the value that defines a statistically significant result at the set alpha level.
proportional hazards model
see Cox’s regression
sigma, uppercase
Read as: “the sum of.”
effect size
A statistical expression of the magnitude of the difference between two treatments or the magnitude of a relationship between two variables, based on the proportional relationship of the difference to the variance.
A-B-A Design
A single-case withdrawal design in which a second baseline phase is introduced
Boolean logic
In literature searches, the terms AND, NOT and OR used to expand or narrow search terms.
intrarater reliability
The degree to which one rater can obtain the same rating on multiple occasions of measuring the same variable.
crossover design
A repeated measures design used to control order effects when comparing two treatments, where half of the sample receives treatment A first followed by treatment B, and the other half receives treatment B first followed by treatment A.
content analysis
A procedure for analyzing and coding narrative data in a systematic way.
maturation effect
A threat to internal validity, in which changes occur in the dependent variable as a result of the passing of time.
ethnography
An approach to qualitative research in which the experiences of a specific cultural group are studied.
two-tailed test
A statistical test based on a nondirectional alternative hypothesis, in which critical values represent both positive and negative tails of a distribution.
gold standard
A measurement that defines the true value of a variable. In criterion-related validity, an instrument that is considered a valid measure and that can be used as the standard for assessing validity of other instruments. In diagnostic testing, a procedure that accurately identifies the true disease condition (negative or positive) of the subject.
open-ended question
A question on a survey (interview or questionnaire) that does not restrict the respondent to specific choices, but allows for a free response.
time-series design
A quasi-experimental design in which performance changes are assessed over time, prior to and following the administration of treatment.
chi square test (x2)
A nonparametric test applied to nominal data, comparing observed frequencies within categories to frequencies expected by chance.
reference standard
A value used as a standard against which to judge a criterion; may or may not be a gold standard. Used to judge criterion-related validity or diagnostic accuracy.
mixed design
A design that incorporates independent variables that are independent (between-subjects) and repeated (within-subjects) factors. Also called a split-plot design.
A-B Design
A single-case design with two phases: A represents the baseline phase, and B represents the intervention phase
PV +
positive predictive value
Estimate of the likelihood that a person who tests positive actually has the disease
trend analysis
Part of an analysis of variance, used to assess trend within data taken over ordered intervals; can express data as linear, quadratic, cubic, and so on, reflecting the number of changes in direction in the data over time.
predictive value of a diagnostic test
Also called posterior probability. Depends on the pretest probability, and the test’s sensitivity and specificity.
random sampling
Probability method of selecting subjects for a sample, where every subject in the population has an equal chance of being chosen.
systematic sample
A probability sampling method where subjects are chosen from lists of population members using specified intervals, such as every 10th person.
q
Studentized range statistic, used in multiple comparison tests.
sampling bias
Bias that occurs when individuals who are selected for a sample overrepresent or underrepresent the underlying population characteristics
a
Alpha level: Level of statistical significance, or risk of Type I eror; maximum probablitlty level that can be achieved in a statistical test to reject the null hypothes.s Symobls a1 and a2 are used to denote level of significance for one- and two-tailed tests.
discriminant analysis
A multivariate statistical technique used to determine if a set of variables can predict group membership.
mode
A measure of central tendency representing the most commonly occurring score.
case-control study
A design in analytic epidemiology in which the investigator selects subjects on the basis of their having or not having a particular disease and then determines their previous exposure.
research hypothesis
A statement of the researcher’s expectations about the relationship between variables under study.
binomial variable is the same as
dichotomy
intercorrelations
A set of bivariate correlations for several variables within a sample.
unpaired t-test
A parametric test for comparing two means for independent samples; also called an independent t-test.
Gaussian distribution
same as normal distribution?
statistical hypothesis
sames as null hypothesis
predictive validity
A form of measurement validity in which an instrument is used to predict some future performance.
univariate analysis
Statistical procedures for analyzing one dependent variable.
celeration line
In single-case research, a line that divides the data points within a phase into two equal halves, indicating the trend of the data within that phase.
number needed to harm (NNH)
The number of patients that need to be treated to observe one adverse outcome.
Rasch analysis
Transformation of items on an ordinal scale to an interval scale, demonstrating the unidimensional nature of a scale.
experimenter effects (experimenter bias)
Biases that are present in research data because of behaviors, expectations, or attitudes of those collecting the data.
forward selection
A process used in stepwise multiple regression that enters variables one at a time into the equation based on the strength of their association with the outcome variable, until all statistically significant variables are included.
X2r
Freidman two-way analysis of variance by ranks:
A nonparametric statistical procedure for repeated measures, comparing more than two treatment conditions of one independant variable; analogous to the one-way repeated measures analysis of variance.
extraneous variable
A variable that confounds the relationship between the independent and dependent variables.
posterior probability
same as posttest probability The probability of a condition existing after performing a diagnostic test; predictive value of a diagnostic test. Also called posterior probability. Depends on the pretest probability, and the test’s sensitivity and specificity
pretest probability
The probability that a condition exists prior to performing a diagnostic test. Equal to the prevalence of the condition in a specified group of subjects. Also called prior probability.
centroid
A point determined from the intersection of two means of two dependent variables (X, Y), used in multivariate analysis.
interaction effect
The combined effect of two or more independent variables on a dependent
meta-analysis
Use of statistical techniques in a systematic review to integrate the results of included studies to determine overall outcome, usually based on effect size.
exempt review
Exemption from review of a proposal by an Institutional Review Board for projects that do not involve direct contact with subjects, presenting no risk.
Wilcoxon rank-sum test
see Mann Whitney U test
cohort study
An observational study design in which a specific group is followed over time. Subjects are classified according to whether they do or do not have a particular risk factor or exposure and followed to determine disease outcomes
SEM
standard error of measurement (SEM) : A reliability measure of response stability, estimating the standard error in a set of repeated scores.
paradigm
A set of assumptions, concepts or values that constitute a way of viewing reality within an intellectual community.
nonequivalent control group
A control group (or comparison group) that was not created by random assignment.
quadratic trend
A nonlinear trend, with one turn in direction.
power
(1-beta) The ability of a statistical test to find a significant difference that really does exist; the probability that a test will lead to rejection of the null hypothesis.
alpha level (a)
level of statistical significance, or risk of Type I eror; maximum probablitlty level that can be achieved in a statistical test to reject the null hypothes.s Symobls a1 and a2 are used to denote level of significance for one- and two-tailed tests.
measurement error
The difference between an observed value for a measurement and the theoretical true score; may be the result of systematic or random effects.
phenomenology
An approach to qualitative research involving the study of complex human experience as it is actually lived.
absolute risk increase (ARI)
The increase in risk associated with an intervention as compared to risk without the intervention (or control condition); the absolute difference between the control event rate (CER) and the experimental event rate (EER)
block
Level of an attribute variable in which subjects are homogeneous on a particular characteristic.
completer analysis
Analysis of data in a clinical trial only for those subjects who complete the study.
standardized residual
In a chi square test, the contribution of each cell to the overall statistic.
preference
In sequential clinical trials, the expression of which treatment is considered better within a sequential pair.
item-to-total correlation
Correlation of individual items in a scale with the total scale score; an indication of internal consistency.
Least squares method
A method of fitting a regression line to a set of bivariate data so as to minimize the sum of the squared vertical deviations of Y values around that line.
relative risk reduction (RRR)
The reduction in risk associated with an intervention relative to the risk without the intervention (control); the absolute difference between the experimental event rate and the control event rate divided by the control event rate.
prior probability
same as pretest probability
crude rate
A rate for a population that is not adjusted for any subset of the population.
mean (X)
A measure of central tendency, computed by summing the values of several observations and dividing by the number of observations.
secondary source
Reference source that represents a review or report of another’s work.
hypothesis
A statement of the expected relationship between variables.
µ
mu
mean of a popluation
criterion-referencing
Interpretation of a score based on its actual value.
withdrawal design
In single-case research, a design that involves withdrawal of the intervention.
parameter
A measured characteristic of a population.
within-subjects design
A research design that incorporates only repeated measures.
dichotomy (dichotomous variable)
A nominal variable having only two categories, such as yes/no and male/female; a binomial variable.
split-plot design
(See mixed design.)
cumulative scale
A scale designed so that agreement with higher-level responses assumes agreement with all lower-level responses.
independent variable
The variable that is presumed to cause, explain or influence a dependent variable; a variable that is manipulated or controlled by the researcher, who sets its “values” or levels.
explained variance
Between-groups variance; that portion of the total variance in a data set that can be attributed to the differences between groups or treatment conditions.
multivariate analysis of variance (MANOVA)
An advanced multivariate procedure that provides a global test of significance for multiple dependent variables using an analysis of variance.
split-half reliability
A reliability measure of internal consistency based on dividing the items on an instrument into two halves and correlating the results.
order effects
The sequential effect of one subject being exposed to several treatments in the same order; potentially manifested as carryover or practice effects.
parametric statistics
Statistical procedures for estimating population parameters and for testing hypotheses based on population parameters, with assumptions about the distribution of variables, and for use with interval or ratio measures.
intention-to-treat
Principle whereby data are analyzed according to group assignments, regardless of how subjects actually completed the study.
statistic
A measured characteristic of a sample.
Scheffé’s multiple comparison test
A multiple comparison procedure for comparing means following a significant analysis of variance. Considered the most conservative of the multiple comparison methods.
odds ratio (OR)
Estimate of relative risk in a case-control study.
Spearman-Brown formula
The statistical procedure used to analyze split-half reliability; also called the Spearman-Brown prophecy formula.
ARIMA (autoregressive integrated moving average)
Statistical technique for analysis of data from time-series studies.
retrospective study
A study that analyzes observations that were collected in the past.
difference score (d)
The difference between two scores taken on the same individual
Accessible population
The actual population of subjects available to be chosen for a study. This group is usually a nonrandom subset of the target population.
rpb
point biserial correlation
A correlation statistic for estimating the relationship between a dichotomy and a continuous variable on the interval or ratio scale
homogeneity of variance
An underlying assumption in parametric statistics that variances of samples are not significantly different.
standard deviation (s)
A descriptive statistic reflecting the variability or dispersion of scores around the mean.
positive liklihood ratio
LR +
A ratio that indicates ow much the odds of a disease are increased if a diagnostic test is positive. Equals sensitivity/(1-specificity)
translational research
Clinical investigation with human subjects in which knowledge obtained from basic research is translated into diagnostic or therapeutic interventions that can be applied to treatment or prevention.
event rate
The proportion of subjects in a group in whom a specific event or outcome is observed. (See control event rate [CER] and experimental event rate [EER].)
grounded theory
An approach to collecting and analyzing data in qualitative research, with the goal of developing theories to explain observations and experience.
sensitivity
A measure of validity of a screening procedure, based on the probability that someone with a disease will test positive.
interval scale
Level of measurement in which values have equal intervals, but no true zero point.
history effect
A threat to internal validity, referring to the occurrence of extraneous events prior to a posttest that can affect the dependent variable.
exploratory research
Research that has as its purpose the exploration of data to determine relationships among variables.
contingency table
A two-dimensional table displaying frequencies or counts, with rows (R) and columns (C) representing categories of nominal or ordinal variables; also referred to as cross-tabulation.
blinding
Techniques to reduce experimental bias by keeping the subjects and/or investigators ignorant of group assignments and research hypotheses.
absolute risk reduction (ARI)
The reduction in risk associated with an intervention as compared to the risk without the intervention (or the control condition); the absolute difference between the experimental event rate (EER) and the control event rate (CER).
correlation
The tendency for variation in one variable to be related to variation in a second variable; those statistical procedures used to assess the degree of covariation between two variables.
predictive value (PV)
(see negative predictive value and positive predictive value)
secondary analysis
An approach to research involving the use of data that were collected for another purpose, usually for the purpose of testing new hypotheses.
reliability
The degree of consistency with which an instrument or rater measures a variable.
scatter plot
A graphic representation of the relationship between two variables.
canonical correlation
A multivariate correlation procedure, whereby two sets of variables are correlated
constant comparative method
Inductive process in qualitative research that calls for continual testing of a theory as data are examined.
difference score (d)
The difference between two scores taken on the same individual.
Bonferroni t
A post hoc method to compare means following an analysis of variance; based on planned comparisons; also called the Dunn multiple comparison procedure.
population
The entire set of individuals or units to which data will be generalized.
validity
- The degree to which an instrument measures what it is intended to measure. 2. The degree to which a research design allows for reasonable interpretations from the data, based on controls (internal validity), appropriate definitions (construct validity), appropriate analysis procedures (statistical conclusion validity), and generalizability (external validity).
zero-order correlation
A bivariate correlation.
X2
chi-square test: A nonparametric test applied to nominal data, comparing observed frequencies within categories to frequencies expected by chance.
pretest-posttest design
An experimental design involving a pretest prior to intervention and a posttest following intervention.
intraclass correlation coefficient (ICC)
A reliability coefficient based on an analysis of variance; a generalizability coefficient.
within-groups variance
same as error variance
Cox’s proportional hazards regression
A regression procedure used when the outcome has not yet occurred (a censored variable). Used in survival analysis.
alphanumeric data
In data processing, the entry of values that contain symbols or letters.
control event rate (CER)
The number of subjects in the control group who develop the outcome of interest.
floor effect
A measurement limitation of an instrument whereby the scale cannot determine decreased performance beyond a certain level.
level of measurement
The precision of a scale based on how a characteristic is measured; nominal, ordinal, interval and ratio levels.
linear regression
The process of determining a regression equation to predict values of Y based on a linear relationship with values of X.
construct validity
- A type of measurement validity; the degree to which a theoretical construct is measured by an instrument. 2. Design validity related to operational definitions of independent and dependent variables.
rs
Spearman’s rank correlation coefficient
a nonparametric correlation prodeure for ordinal data. Also called Spreaman’s rho
statistical regression
same as regression towards the mean
treatment-received analysis
Analysis of subject data in an experiment according to the treatment subjects actually did receive, regardless of their original group assignment.
serial dependency
Correlation in a set of data collected over time, in which one observation can be predicted based on previous observations.
test-retest reliability
The degree to which an instrument is stable, based on repeated administrations of the test to the same individuals over a specified time interval.
area probability sample
A form of cluster sampling in which geographic areas serve as the units of analysis.
concurrent validity
A type of measurement validity; a form of criterion-related validity; the degree to which the outcomes of one test correlate with outcomes on a criterion test, when both tests are given at relatively the same time.
historical research
Research that seeks to examine relationships and facts based on documentation of past events.
dft
For analysis of variance,
= total degrees of freedom
median
A measure of central tendency representing the 50th percentile in a ranked distribution of scores; that is, that point at which 50 percent of the scores fall below and 50 percent fall above.
face validity
The assumption of validity of a measuring instrument based on its appearance as a reasonable measure of a given variable.
quasi-experimental research
Comparative research approach in which subjects cannot be randomly assigned to groups or control groups are not used.
bivariate statistics
Statistics involving the analysis of two variables for the purpose of determining the relationship between them, for example, correlation.
main effect
The separate effect of one independent variable in a multifactor design.
Likert scale
A summative scale based on responses to a set of statements for which respondents are asked to rate their degree of agreement or disagreement.
negative likelihood ratio
NR -
A ratio that indicates how much the odds of a disease are decreased if a diagnostic test is netagive
Equals specificity/(1-sensitivity)
cut-off score
Score used as the demarcation of a positive or negative test outcome.
X-bar
mean of a sample
canonical correlation
A multivariate correlation procedure, whereby two sets of variables are correlated.
selection bias
A threat to internal validity in which bias is introduced by initial differences between groups, when these differences are not random.
minimal detectable difference (MDD)
That amount of change in a variable that must be achieved to reflect a true difference; the smallest amount of change that passes the threshold of error. Also called minimal detectable change (MDC).
stem-and-leaf plot
A graphic display for numerical data in a frequency distribution showing each value in the distribution.
operational definition
Definition of a variable based on how it will be used in a particular study; how a dependent variable will be measured, how an independent variable will be manipulated.
internal consistency
A form of reliability, assessing the degree to which a set of items in an instrument all measure the same trait. Typically measured using Cronbach’s alpha
multiple comparison test
A test of differences between individual means following analysis of variance, used to control for Type I error.
Kaplan-Meier Estimate
A common method of determining survival time which generates a step function, changing the survival estimate each time a patient dies (or reaches the terminal event).
multistage sampling
same as cluster sampling?
clinical prediction rule
A statistical tool that quantifies the relative contribution of examination and history findings to determine a diagnosis, prognosis, or likely response to intervention.
cluster analysis
A form of probability sampling in which large subgroups (clusters) are randomly selected first, and then smaller units from these clusters are successively chosen; also called multistage sampling.
special cause variation
Fluctuation in response caused by known factors that results in nonrandom and unexpected performance.
multiple baseline design
In single-case research, a design for collecting data for more than one subject, behavior, or treatment condition. Baseline phases are staggered to provide control.
Cronbach’s alpha
Reliability index of internal consistency, on a scale of 0.00 to 1.00.
expedited review
Accelerated review of a proposal by an Institutional Review Board, based on minimal risk.
normative research
A descriptive research approach designed to determine normal values for specific variables within a population.
correlational research
A descriptive research approach that explores the relationship among variables without active manipulation of variables by the researcher.
polynomial regression
Regression procedure for nonlinear data.
inferential statistics
That branch of statistics concerned with testing hypotheses and using sample data to make generalizations concerning populations.
analysis of variance (ANOVA)
Statistical procedure appropriate for comparison of three or more treatment groups or conditions, or the simultaneous manipulation of two or more independent variables; based on the F statistic.
minimal clinically important difference (MCID)
The smallest difference in a measured variable that signifies an important rather than trivial difference in the patient’s condition. The smallest difference a patient or clinician would perceive as beneficial, and that would result in a change in the management of the patient. Also called minimal clinically important change (MCIC) or minimally important change (MIC).
Beta
Probability of making a Type II error.
convenience sampling
A nonprobability sampling procedure, involving selection of the most available subjects for a study.
survival analysis
Multivariate analysis to estimate survival time, or time to a defined outcome, based on probabilities that an individual will achieve the outcome.
refereed journal
Journals that utilize a peer review process to evaluate manuscript submissions as a basis for choosing which ones will be published.
McNemar test
A nonparametric statistical test for nominal level measures, for correlated samples; a form of the chi square test.
significance level
same as alpha level
directional hypothesis
A variable that can only be measured in separate units and that cannot be measured in intervals of less than 1.
Two standard deviation band method
A method of data analysis in single-subject research.
relative risk (RR)
Estimate of the magnitude of the association between an exposure and disease, indicating the likelihood that the exposed group will develop the disease relative to those who are not exposed.
effectiveness
Benefits of an intervention as tested under “real world” conditions, often using quasi-experimental methods.
nonparametric statistics
A set of statistical procedures that are not based on assumptions about population parameters, or the shape of the underlying population distribution; most often used when data are measured on the nominal or ordinal scales.
nonprobability sample
A sample that was not selected using random selection.
X-Xhat
The distance of a single data point from the mean of the distribution. The summ of the deviation scores for a given distribution will awlays equal zero.
between-groups variance
That portion of the total variance in a set of scores that is attributed to the difference between groups.
number needed to treat (NNT)
The number of patients that need to be treated to prevent one adverse outcome or achieve one successful outcome; the reciprocal of absolute risk reduction (ARR).
d
Difference Score: The difference between two scores taken on the same individual
nested design
A multifactor design in which one variable is not crossed with other variables.
criterion-related validity
A type of measurement validity; the degree to which the outcomes of one test correlate with outcomes on a criterion test; can be assessed as concurrent validity or predictive validity.
systematic error
A form of measurement error, where error is constant across trials.
pooled variance estimate
Estimate of population variance based on the weighted average of sample variances; used in the unpaired t-test when group variances are not significantly different (under conditions of homogeneity of variance).
Latin square
A matrix of columns and rows used to assign sequences of treatments to control for order effects.
confounding
The contaminating effect of extraneous variables on interpretation of the relationship between independent and dependent variables.
normal distribution (curve)
A symmetrical bell-shaped theoretical distribution that has defined properties; also called a Gaussian distribution.
method error (ME)
A form of reliability testing for assessing response stability based on the discrepancy between two sets of repeated scores.
ceiling effect
A measurement limitation of an instrument whereby the scale cannot determine increased performance beyond a certain level.
gain score
same as change score?
interrater reliability
The degree to which two or more raters can obtain the same ratings for a given variable.
false negative
A test result that is negative in a person who has the disease or condition of interest.
responsiveness
The ability of a test to demonstrate change.
error variance
That portion of the total variance in a data set that cannot be attributed to treatment effects, but that is due to differences between subjects.
washout period
In a crossover design, that period of time between administration of the two treatments, allowing effects of the experimental treatment to dissipate.
sequential clinical trial
Experimental research design that allows consecutive entrance to a clinical trial and continuous analysis of data, permitting stopping of the trial when data are sufficient to show a significant effect.
participant observation
A method of data collection in qualitative research in which the researcher becomes a participant in the group that is being observed.
random assignment
Assignment of subjects to groups using probability methods, where every subject has an equal chance of being assigned to each group.
discriminant validity
An approach in construct validation assessing the degree to which an instrument yields different results when measuring two different constructs; that is, the ability to discriminate between the constructs.
percent agreement
A reliability test for categorical variables, estimating the ability of researchers to agree on category ratings.
between subjects factor
An independent variable for which levels are applied to independent groups.
Yates’ correction for continuity
In the chi square test, a correction factor applied when expected frequencies are too small, effectively reducing the chi square statistic.
risk-benefit ratio
An ethical principle that is an element of informed consent, in which the risks of a research study to the participant are evaluated in relation to the potential benefits of the study’s outcomes.
sigma
Standard deviation of a population.
cross-tabulation
same as contingency table. A two-dimensional table displaying frequencies or counts, with rows (R) and columns (C) representing categories of nominal or ordinal variables; also referred to as cross-tabulation.
Hawthorne effect
The effect of subjects’ knowledge that they are part of a study on their performance.
confidence interval (CI)
The range of values within which a population parameter is estimated to fall, with a specific level of confidence.
observational study
A study that does not involve an intervention or manipulation of an independent variable.
rho
Correlation coefficient for a population.
probability sample
A sample chosen using randomized methods.
multivariate analysis
A set of statistical procedures designed to analyze the relationship among three or more variables; includes techniques such as multiple regression, discriminant analysis, factor analysis and multivariate analysis of variance.
sp2
Pooled variance estimate
Estimate of population variance based on the weighted average of sample variances; used in the unpaired t-test when group variances are not significantly different (under conditions of homogeneity of variance)
expected frequencies
In a contingency table, the frequencies that would be expected if the null hypothesis is true; frequencies that are expected just by chance.
coefficient of variation (CV)
A measure of relative variation; based on the standard deviation divided by the mean, expressed as a percentage.
SpPin
When a test has high specificity, a positive test rules in the diagnosis.
post hoc comparisons
Multiple comparison tests that follow an analysis of variance.
within-subjects factor
same as a repeated measure
covariate
An extraneous variable that is statistically controlled in an analysis of covariance, so that the relationship between the independent and dependent variables is analyzed with the effect of the extraneous factor removed.
Deviation score (X-Xhat)
The distance of a single data point from the mean of the distribution. The summ of the deviation scores for a given distribution will awlays equal zero.
Σ
read as “the sum of”
active variable
An independent variable with levels that can be manipulated and assigned by the researcher.
R squared
Multiple correlation coefficient squared; represents the proportion of variance in Y explained by several independent variables in a multiple regression equation.
attrition (experimental mortality)
A threat to internal validity, referring to the differential loss of participants during the course of data collection, potentially introducing bias by changing the composition of the sample.
MANOVA
multivariate analysis of variance (MANOVA) An advanced multivariate procedure that provides a global test of significance for multiple dependent variables using an analysis of variance.
beta weight
In a multiple regression equation, the standardized weight for each independent variable.
1-beta
power. The ability of a statistical test to find a significant difference that really does exist; the probability that a test will lead to rejection of the null hypothesis.
regression toward the mean
A statistical phenomenon in which scores on a pretest are likely to move toward the group mean on a posttest because of inherent positive or negative measurement error; also called statistical regression.
residual
In regression analysis, the difference between the value of the dependent variable predicted by the regression equation and the actual value.
standardized response mean (SRM)
One approach to evaluating effect size with change scores. Calculated as the difference between pretest and posttest scores, divided by the standard deviation of the change scores.
Spearman’s rank correlation coefficient
A nonparametric correlation procedure for ordinal data. Also called Spearman’s rho.
Freidman two-way analysis of variance by ranks (X2r)
A nonparametric statistical procedure for repeated measures, comparing more than two treatment conditions of one independant variable; analogous to the one-way repeated measures analysis of variance.
randomized block design
An experimental design in which one independent variable is an attribute variable, creating homogeneous blocks of subjects who are then randomly assigned to levels of the other independent variable.
instrumentation effect
A threat to internal validity in which bias is introduced by an unreliable or inaccurate measurement system.
Type I error
An incorrect decision to reject the null hypothesis, concluding that a relationship exists when in fact it does not.
- df*b
For analysis of variance,
= between groupus degrees of freedom
LR +
positive liklihood ratio
A ratio that indicates ow much the odds of a disease are increased if a diagnostic test is positive. Equals sensitivity/(1-specificity)
content validity
A type of measurement validity; the degree to which the items in an instrument adequately reflect the content domain being measured.
external validity
The degree to which results of a study can be generalized to persons or settings outside the experimental situation.
Y - Yhat
residual
In regression analysis, the difference between the value of the dependent variable predicted by the regression equation and the actual value
developmental research
A descriptive research approach designed to document how certain groups change over time on specific variables.
Levene’s test
A test of the equality of variances, used with the independent t test and the analysis of variance.
one-way analysis of variance
An analysis of variance with one independent variable.
cumulative incidence (CI)
The number of new cases of a disease during a specified time period divided by the total number of people at risk; the proportion of new cases of a disease in a population.
variance
A measure of variablity in a distribution, equal to the square of the standard deviation.
central tendency
Descriptive statistics that represent “averages” or scores that are representative of a distribution; includes mean, median, and mode.
t-test
A parametric test for comparing two means; also called Student’s t-test. (See paired t-test and unpaired t-test.)
Kruskal-Wallis one-way analysis of variance by ranks (H)
A nonparametric statistical procedure for comparing more than two independent groups representing levels of one independent variable; analogous to the one-way analysis of variance.
statistical significance
The term indicating that the results of an analysis are unlikely to be the result of chance at a specified probability level; rejection of the null hypothesis.
standarized residual
in a chi square test, the contribution of each scell to the overall statistic
trend
- The shape of a distribution of scores taken over time, reflecting the distribution’s linearity or lack of linearity. 2. In single-case research, the direction of change in the target behavior within a phase or across phases.
dependent variable
A response variable that is assumed to depend on or be caused by another (independent) variable.
Pooled variance estimate
sp2
Estimate of population variance based on the weighted average of sample variances; used in the unpaired t-test when group variances are not significantly different (under conditions of homogeneity of variance)
censored observation
An observation whose value is unknown because the subject has not been in the study long enough for the outcome to have occurred; used to estimate survival curves.
percentile
The percentage of a distribution that is below a specified value. Data are divided person-years. The total number of years that a set of subjects have participated in a study, typically used when subjects begin and end their participation at different times.
Fisher’s exact test
A nonparametric procedure applied to nominal data in a 2 X 2 contingency table, comparing observed frequencies within categories to frequencies expected by chance. Used when samples are too small to use the chi-square test.
treatment arm
Another term for each independent group in a clinical trial.
deductive reasoning
The logical process of developing specific hypotheses based on general principles.
slope
- In regression analysis, the rate of change in values of Y for one unit of change in X. 2. In single-case research, the rate of change in the magnitude of the target behavior over time.
statistical process control (SPC)
A method of charting production outcomes over time to identify and monitor variances; can be used as a method of analysis for single-subject designs.
point biserial correlation
A correlation statistic for estimating the relationship between a dichotomy and a continuous variable on the interval or ratio scale.
multicolinearity
The correlation between independent variables in a multiple regression equation, causing them to provide redundant information.
