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MHS > Measurements in population > Flashcards

Measurements in population Flashcards

1
Q

Absolute risk

A

The probability of an event in a population under study [contrasted with the RELATIVE RISK]. Synonymous with INCIDENCE.

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2
Q

Absolute risk reduction

A

The amount, sometimes expressed as a percentage, by which the risk of a disease is reduced by elimination or control of a particular exposure. It is possible from this to estimate the number of people spared the consequences of an exposure.

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3
Q

Adverse reaction

A

Syn: adverse outcome. An unwanted or undesirable consequence of a diagnostic, preventive, or therapeutic regimen or procedure, e.g. illness caused by immunization against childhood infections.

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4
Q

Age specific (incidence) rate

A

An incidence rate for a specified age group. The numerator and denominator refer to the same age group.

Example:
Number of deaths among residents
Age-specific death rate = age 25-34 in an area in a year x 100,000/Average (e.g. midyear) population age 25-34 in the area in that year

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5
Q

Age specific mortality rate

A

A specific type of incidence rate in which the numerator is the number of deaths observed in a specified age group.

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6
Q

Age standardisation

A

Syn: age adjustment. Mathematical procedures for adjusting rates in two or more populations with differing age structures so as to adjust for rate differences among them that are or could be attributable to the effect of age differences, rather than other factors.. See also STANDARDIZATION.

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7
Q

Algorithm

A

A systematic process consisting of an ordered sequence of stages in which each stage is determined by the outcome of the stage that preceded it.

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8
Q

Analysis of variance

A

Syn: ANALYSIS OF VARIANCE. A set of statistical methods for assessing the contribution of independent variables to the mean value of a continuous dependent variable.

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9
Q

Arithmetic mean

A

A measure of central tendency, computed by adding all the values in the set and dividing by the number of values in the set. See also AVERAGE.

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10
Q

Attack rate

A

The CUMULATIVE INCIDENCE rate of a condition in a particular population or group of people such as patients admitted to a hospital.

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11
Q

Attributable risk

A

The risk of disease or death in the exposed group minus the risk of disease or death in the unexposed group.

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12
Q

Binary variable

A

A variable having only two possible values, e.g., on or off, 0 or 1, male or female. Also known as a discontinuous variable. Cf. CONTINUOUS VARIABLE.

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13
Q

Birth cohort

A

The component of the population born during a specified period, generally a year, sometimes a 5- or 10-year period

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14
Q

Birth rate

A

The number of live births in a defined population, in a (usually) calendar year divided by the midyear population, with the customary multiplier of 1,000 to produce a whole number rather than a decimal or faction.

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15
Q

Censoring

A

A term used in biostatistics to describe loss of cases to follow-up.

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16
Q

Census

A

A periodic enumeration of the population, primarily intended to collect information to identify eligible voters, tax payers, and sometimes to identify people eligible for military service, and incidentally many other useful facts, e.g., about housing conditions. Censuses are of two broad types – de facto, in which people are enumerated where they are on a given day or night and de jure, when they are enumerated related to where they habitually live. The UK censuses, carried out every 10 years are de facto, thus, for university students, for example, if the census day or night falls in university term they will contribute to the numbers of people in the relevant university town or city. If the day or night falls during university vacation, they are enumerated in relation to where they are at that time – most will be elsewhere.

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17
Q

Central tendency

A

The grouping of numerical data about a value at or near the midpoint of the overall distribution. Three common MEASURES OF CENTRAL TENDENCY are mean, median, and mode

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18
Q

Chi-square (χ2) test

A

A common statistical test for detecting whether two or more populations differ from one another with respect to the proportions of people in those populations that have a given characteristic. Cf. STUDENT’S T TEST.

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19
Q

Cluster sampling

A

A sampling method is which each unit selected is a group of people (e.g. a family, a household, a school or class within a school).

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20
Q

Competing risk

A

An event that removes a study subject from experiencing the outcome that is under investigation. For instance, in a study of smoking in relation to lung cancer, death of coronary heart disease or in a road traffic accident is a competing risk.

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21
Q

Confidence interval

A

The range within which the true value of a variable such as a mean, proportion, or rate lies, with a probability that can be calculated using statistical methods. The end points of the confidence interval are the confidence limits.

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22
Q

Confidence limits

A

The upper and lower boundaries of the confidence interval.

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23
Q

Contingency table

A

A table that arranges sets of data in columns and rows so that relationships between the sets can be studied by means of suitable statistical tests, e.g., the CHI-SQUARE TEST.

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24
Q

Continuous variable

A

Data (variables) with a potentially infinite number of possible values along a continuum. Data representing a continuous variable include height and weight, BMI, age, blood pressure etc. Cf. BINARY VARIABLE.

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25
Q

Control group, controls

A

Subject with whom comparison is made in a case control study, randomized controlled trial, or other variety of epidemiological study.

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26
Q

Convenience sample

A

A sample, usually of people, that has been collected by expedient means, such as that they happen to be available for study, not by using a random sampling method.

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27
Q

Correlation coefficient

A

A statistical measure of the degree of relationship between two variables. It is represented by the symbol r and in practice it usually refers to a linear relationship that in theory can vary from +1 when there is perfect correlation to -1 when the two variables are perfectly inversely related.

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28
Q

Crude death rate

A

Syn: crude mortality rate. The frequency of death in a specified population during a specified period. It is calculated by dividing the number of deaths in the period by the estimated number of people at risk of dying during this period, usually a calendar year. It is called the “crude” death rate because no adjustment is made to allow for age composition of the population or for other conditions or circumstances. Thus, comparisons of crude death rates in different populations have limited value and must be interpreted with caution.

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29
Q

Cumulative incidence

A

The number of new cases of a disease or new health-related events in a defined population within a specified period of time, the specified period of time being the same for each person.

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30
Q

Cut-off point

A

Syn: cut point. An arbitrarily chosen value (though based as closely as possible on evidence of likely harm), such as the level of systolic and / or diastolic blood pressure, that is used to designate hypertension. The distinction between “normal” and “abnormal”.

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31
Q

Death rate

A

Syn: MORTALITY RATE. The frequency with which death occurs among a designated population during a designated period, usually a calendar year. Calculated by dividing the number of deaths (the numerator) by the number of people at risk in the population in which the deaths are occurring.

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32
Q

Degrees of freedom

A

A term used in STATISTICS to describe the number of independent comparisons that can be made between the variables in a study.

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33
Q

Dependent variable

A

In statistics, a variable the value of which is affected by other variable(s).

34
Q

Experimental epidemiological studies

A

Studies in which exposure is determined as part of the study design. This includes randomised and non-randomised clinical trials. Syn: INTERVENTIONAL EPIDEMIOLOGICAL STUDIES

35
Q

Fatality rate

A

The death rate observed in a designated series of people affected by a simultaneous event, e.g., victims of a disaster, or by a specified condition.

36
Q

Haphazard sample

A

A group that is selected without regard for any rigorous method of sampling, without using either a random allocation procedure or a systematic non-random sampling method, such as every tenth name in a telephone directory.

37
Q

Hawthorne effect

A

Any effect on the behavior of individuals and groups due to knowing that they are under observation. Frequently this knowledge promotes behavior that those observed believe the observer(s) expect(s) or hope(s) to see, i.e., the effect is usually beneficial.

38
Q

Heterogeneity

A

The degree of “unlikeness” with a group or community (e.g. in a group of randomised controlled trials being analysed in a META-ANALYSIS).

39
Q

Incidence

A

The number of new cases of a disease or new health-related events in a defined population within a specified period of time.

40
Q

Incidence density

A

The number of new cases of a disease or new health-related events in a defined population within a specified period of time when the periods of observation for each individual are not the same. Incidence density uses person-time (e.g. person years or person months of exposure.

41
Q

Independent variable

A

In a research study, the characteristic, quality, or entity that is hypothesized to influence DEPENDENT VARIABLES that are being measured.

42
Q

Lifetime risk

A

The probability, often expressed as a percentage, that at some stage in life a person will develop a designated condition, specifically cancer. For example, there is a lifetime risk of about 25% of getting cancer, and a lifetime risk of about 20% of dying of cancer in upper-income countries.

43
Q

Loss to follow up bias

A 
Erroneous conclusions (e.g. to a COHORT STUDY) as a consequence of LOSS TO FOLLOW-UP.
The general term for all original participants in a COHORT or other long-term study who cannot or do not take part in further phase(s) for any reason, e.g., death, refusal, being untraceable, or having moved away from the study region.
44
Q

Masking

A

Syn: BLINDING. In clinical trials, the process of withholding the identities of study subjects in treatment and control groups, usually described as “blinding”. The word “masking” is preferred to “blinding” by some clinical trial specialists on the grounds that “blinding” may be an emotive word.

45
Q

Matching

A

The process of making a study group and a comparison group comparable with respect to extraneous (CONFOUNDING) factors (such as age, sex, ethnicity etc.).

46
Q

Measures of central tendency

A

A general term for several parameters related to the distribution of variables around some “central” value. These parameters are the MEAN, MEDIAN, and MODE. The median is the value at the point where exactly half the values in a set are higher and half are lower when all the values in a set are arranged in sequence. The mode is the most commonly occurring value in the set. The mean can be one of three kinds: the arithmetical mean is the sum of all the values in a set divided by the number of values in the set; the geometric mean is calculated by adding the logarithms of all the values in the set, dividing by the number of values, and taking the antilogarithm of this number; and the harmonic mean is the sum of the reciprocals of the values in a set, divided into the number of values in the set.

47
Q

Mortality rate

A

Syn: DEATH RATE. A general term for rates compiled from data on the number of deaths in relation to a specified population at risk. Several common variations are crude mortality rate, age-, sex-, and cause-specific mortality rates, and adjusted mortality rates. See also RATE, RISK and ADJUSTMENT.

48
Q

Multiple regression

A

A set of statistical techniques used, e.g., in sociological and epidemiological analyses, when many variables are involved. These tests commonly used include linear regression analysis and logistic regression analysis.

49
Q

Nominal data

A

Data that are identified in terms of their names (or numbers, used as labels rather than as numerical value) without regard for other qualities, such as rank and amount.

50
Q

Nominal scale

A

A classification method that organizes data according to specified qualitative criteria, such as country of birth, ethnic origin, without regard for any quantitative criteria, such as socioeconomic status.

51
Q

Nonparametric method

A

Syn: distribution-free method. A statistical method that can be used regardless of the manner in which the data to be analyzed are distributed.

52
Q

Normal distribution

A

A distribution that is symmetrical about a midpoint, with the largest number of values clustered closest to this and diminishing further away. Also called GAUSSIAN DISTRIBUTION.

53
Q

Null hypothesis

A

The proposal that one variable has no association with another or that two populations do not differ from one another.

54
Q

null hypothesis prediction

A

The predicted value of the odds ratio, relative risk or other effect size if the null hypothesis is true – one (unity) for odds ratio or relative risk and zero for the degree of difference, for example, in the quantitative effect on blood pressure of two drug interventions.

55
Q

Odds

A

The statistical calculation of the number of events as a fraction of nonevents or as a fraction of all that are theoretically possible. For instance, in the roll of a six-sided die, the odds that a specific number will roll to the top are 1 in 6.

56
Q

Odds ratio

A

Syn: cross-products ratio. Strictly speaking, the ratio of two odds, but as used in the analysis of data from a case control study, a simple calculation that yields an approximate value for the RELATIVE RISK of the exposure that has been examined in a CASE CONTROL STUDY. The odds ratio is best explained in a simple table
The odds ratio is ad/bc. The odds ratio yields an approximation of RELATIVE RISK that is valid for rare and uncommon diseases but not for diseases with an incidence rate greater than about 1/100.

57
Q

Ordinal scale

A

A system of classification into ordered categories, e.g., a socioeconomic grouping according to income and/or educational level. Contrast NOMINAL SCALE.

58
Q

p, P

A

The abbreviation for the estimated probability of a result equal to or more extreme than that observed in a study, often appearing in publications together with the symbol < for “less than”. . Conventionally, a probability of less than 1 in 20, i.e., p<0.05, is considered unlikely to have occurred by chance in many situations arising in medicine, e.g., results of clinical trials, CONFIDENCE INTERVALS usually convey more information about the uncertainty attaching to an estimate than do p values, and are therefore a preferable way to express results of a study.

59
Q

Period prevalence

A

The number (or proportion) of individuals known to have a disease or health-related state in a given population during a specified time period.

60
Q

Point prevalence

A

The number (or proportion) of individuals known to have a disease or health-related state in a given population at a specified point in time.

61
Q

Poisson distribution

A

A distribution function to describe rare events such as cases of uncommon diseases.

62
Q

Precision

A

The quality of being exactly or sharply defined. For example, a measurement of length expressed to decimal places of millimetres is more precisely defined than one given to the nearest metre. To be distinguished from ACCURACY.

63
Q

Prevalence

A

The number (or proportion) of individuals known to have a disease or health-related state in a given population.

64
Q

Proportional morality ratio (PMR)

A

The number of observed deaths from a specified cause in a defined population divided by the number of deaths that would be expected in a standard population, with both numbers expressed as a proportion of all deaths. The PMRs of specific occupational groups are sometimes used to determine whether their mortality experience differs significantly from that of the general population, justifying further investigation.

65
Q

Quota sampling

A

A sampling method in which the proportions vary in designated subgroups according to such criteria as age group, occupation, social class etc.

66
Q

Random allocation

A

Allocation of persons or entities, such as therapeutic regimens, by a formal process using an accepted method of random sampling, such as a table of random numbers. Used in RANDOMISED CONTROLLED TRIALS.

67
Q

Random error

A

The portion of the variations of measurements and other observations that is due to the operation of chance alone. Random error increases in size and importance if sampling methods are poorly chosen and response rates are low.

68
Q

Random sample

A

Syn: probability sample. A sample drawn by a process of RANDOM ALLOCATION from a population in a manner aimed at ensuring representativeness.

69
Q

Rate

A

A measure of the frequency with which specified events occur in a defined population in a designated period of time. Rates have three components: a numerator, the number of events; a denominator, the numbers in the population at risk of experiencing the event; and a time dimension, the period over which the events occur.

70
Q

Ratio

A

The result of dividing one quantity by another without regard for details such as time dimension. Rates, proportions, and percentages are all types of ratios. The distinction between a proportion and a ratio is that, whereas the numerator of a proportion is included in the population defined by the denominator, this is not necessarily so for a ratio, which expresses the relationship of two separate and distinct quantities, neither of which is included in the other. See also PROPORTION and RATE.

71
Q

Relative risk

A

Syn: risk ratio, hazard ratio. The ratio of the risk of disease or death among the exposed group to the risk among the unexposed. I.e. the incidence of the disease or death in the exposed group divided by the incidence in the unexposed.

72
Q

Response (rate)

A

The proportion, percentage, or fraction of individuals who reply to inquiries that have been directed to all the individuals in a population, or a representative sample of them. The VALIDITY of findings or results and conclusions derived from them is dependent on the response rate. It the response rate is low, i.e., if there are large proportions of nonresponders, the VALIDITY of the results is dubious, even if impeccable sampling methods have been used, because of the magnitude of random error.

73
Q

Standard error

A

The standard if deviation of an estimate. The term often refers to the standard deviation of the observed mean, represented by the symbol σ and calculated from a sample and the true population mean.

74
Q

Standard deviation

A

The most widely used measure of spread or dispersion from the central value of a frequency distribution. It is the positive square root of the variance from the mean or central value of the individual measurements in the distribution.

75
Q

Standard population

A

A population used for STANDARDIZATION. Any population can be used for this purpose provided its age and sex structure are precisely known.

76
Q

Standardisation

A

A set of techniques (DIRECT STANDARDISATION and INDIRECT STANDARDISATION) used to remove as much as possible the effects of differences in confounders (such as age, sex, ethnicity, social class) when comparing two or more populations.

77
Q

Standardised mortality ratio (SMR)

A

The ratio of the number of deaths observed in the study group or population to the number that would be expected if the study population had the same stratum specific rates as the standard population. Usually expressed as a percentage.

78
Q

Standardized incidence ratio

A

The ratio of the incident number of cases of a condition in the study population to the number that would be expected if the study population had the same incidence rate as a standard population. This is an infrequently used parameter.

79
Q

Stratification

A

The process of or result of separating a sample into several sub samples according to specified criteria (usually of a confounder such as age, sex, ethnicity etc.).

80
Q

Student’s t test

A

A statistical test for the degree of similarity or difference between two or more distributions, invented by the British mathematician W.S. Gossett, who published under the pseudonym “Student” because of the conditions of his employment. Cf. Chi square

81
Q

t-distribution

A

A mathematical model that defines the relationship between two or more sets of data, used to determine whether they are significantly different.

82
Q

Weighting

A

A method of adjustment to allow for differences between the study population and a “standard” one, between two or more populations that are being compared, or among any set of variables in which confounding factors might otherwise invalidate comparisons. It can be done in several ways, often by taking different predetermined proportions from several parts of the study population or set of variables, to ensure that numbers in each are sufficient to yield stable rates.

MHS (5 decks)

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