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.