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170 Cards in this Set
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attributable risk

The difference between the risks of an exposed group and an unexposed
group. 

adjusted analysis

An analysis in which statistical account is made for potential confounding
factors, so that an estimate of the independent effect of a risk factor can be made. 

cohort

A group of subjects followed over time


competing risks

Events that prevent the observation of a possible endpoint.


confounding

An indirect association of an exposure with a disease. ___ is due to
the association of the exposure with a ___ factor which is related to the disease. 

effect

The magnitude of a difference or relationship.


event

A clinical outcome of importance. Examples include onset of a disease (such
as cancer or heart disease), onset of a particular symptom (such as bleeding or depression), disease recurrence, or death. 

hypothesis test

A statistical analysis used to accept or reject a null hypothesis.


incidence

The risk or rate or occurrence of new cases of a disease.


matched analysis

Choosing exposed and unexposed subjects to have the same or similar values
of some trait or exposure. typically done to control confounding. 

null hypothesis

The hypothesis being tested about a population. generally means “no
difference” and thus refers to a situation in which there is no difference (e.g., between the means in a treatment group and a control group). 

prevalence

The proportion of individuals who have a particular disease or trait in a given
population. 

pvalue

The probability of observing a result as extreme as or more extreme than the
one actually observed based on chance alone (i.e., if the null hypothesis is true). 

rate

A measure of event frequency; the speed with which events happen, relative
to the size of the population experience observed 

rate ratio

A relative risk measure in which the numerator is the rate at which an event
occurs in an exposed group, and the denominator is the rate in an unexposed group. 

relative risk

Any relative measure of association. A ratio in which the numerator
describes the occurrence of events (risk, rate, odds or hazard) in an exposed group, and the denominator describes the occurrence of events in an unexposed group. 

restricted analysis

Confining the analysis to one group of subjects to minimize confounding.


risk

The probability that an event will occur in a defined period of time.


risk factor

An exposure associated with the occurrence of a disease or outcome.


risk ratio

A relative risk measure in which the numerator is the probability of an event
occurring in an exposed group, and the denominator is the probability in an unexposed group. 

statistical significance level

The probability of making a type I error in a hypothesis test.


stratum

A grouping of subjects, typically formed for the purposes of adjustment (e.g.
age groups). 

test statistic

The specific statistic used to test the null hypothesis (e.g., the t statistic)


type I error

The error that results when one rejects the null hypothesis when it is true or
when one concludes that there is a difference when there is none. 

type II error

The error that results when one does not reject the null hypothesis when it is
false or when one does not detect a difference when there is a difference. 

adjusted rate

A computed disease rate that takes into account the characteristics of the
population so that rates in different locales can be compared despite differences in these characteristics. Typical adjustment factors are age and gender. 

attack rate

The incidence of disease occurring during a limited period of risk (e.g., the
time span of a food borne outbreak of gastroenteritis). 

casefatality

The proportion (percent) of people with a disease who die within a specified
time after disease onset. 

crude rate

A disease rate that include all persons in a population without distinction
with regard to age, gender, race, etc. 

disease register

A database of information regarding all cases of certain diseases that occur in
a specified population during a specified time period. (Examples: State or hospital cancer __. The former is populationbased; the latter is not.) 

incidence rate

The rate of development of new cases of a disease; usually expressed as
cases per thousand (or per 10 thousand or per 100 thousand) person years. Contrast with prevalence. 

infant mortality rate

The number of deaths of children under 12 months (one year) old in a given
year divided by the total number of live births in that year, times 1000 (per 1000). 

maternity mortality rate

the number of deaths related to pregnancy of pregnant women in a year
divided by the number of live births in that year, times 100,000 (per 100,000). 

mortality rate

The incidence rate of death.


neonatal mortality rate

The number of deaths of children under 28 days (4 weeks) old in a given year
divided by the total number of live births in that year, times 1000 (per 1000). 

notifiable disease

A disease for which notification of local (usually state) health authorities is
required. 

perinatal mortality rate

The number of fetal deaths occurring 28 weeks or later in a pregnancy plus
deaths in the first week of life divided by the number of live births and fetal deaths 28 weeks or more in that year, times 1000 (per 1000). 

prevalence

The proportion of a population that has a disease (or a trait) and some point
in time. Contrast with incidence. 

secondary attack rate

The incidence of disease among contacts or household members following
the occurrence of a primary case. The period of observation is specified and is usually brief. 

specific rate

A disease rate for a specific subpopulation of individuals


third party payer

A health insurance provider


censored data

In survival analysis, when the survival time for an individual is not
observed because the individual was still alive at the end of the study or the subject is lost to followup. 

chisquared statistic

The test statistic from a chisquared test.


chisquared test

A statistical test for evaluating association between two variables in a
contingency table. In a 2 × 2 table, this test is equivalent to comparing proportions in two groups of patients. 

contingency table

A rectangular array of numbers, typically crossclassifications of subjects
into categories of two measurements 

independent samples ttest

A statistical test for comparing the means on a continuous measurement
for two separate groups of individuals. For example, this test can be used to compare mean systolic blood pressure in males versus females. 

KaplanMeier method

A procedure for estimating a survival function from survival data in the
presence of censoring. Also called productlimit method. 

lifetable

A tabulation showing the survival experience of a group of subjects over
time. Specifically, shows the survival function estimated from data. 

logrank test

A statistical test for comparing two survival curves.


median survival

The time at which 50% of the individuals have experienced the event of
interest. The timepoint at which the survival function crosses 50%. 

pairedsamples ttest

A statistical test for comparing the means of paired continuous
measurements. This test is usually applied to the case where a single individual is observed on 2 occasions (e.g., before and after a drug intervention). 

productlimit method

A procedure for estimating a survival function from survival data in the
presence of censoring. Also called KaplanMeier method. 

survival analysis

Statistical evaluation of timetoevent data. Examples include time to
death, time to disease progression, and time until onset of disease. 

survival curve

A graph of a survival function.


survival function

Describes the probability that an individual will survive beyond a specific
point in time. 

survival time

Data measured as the time until an event (such as death) occurs.


coefficient of determination

Usually denoted by R^2, in linear regression analysis, this is the proportion
of total variation in the dependent variable explained by the independent variable(s). 

correlation coefficient

Usually denoted by r, this is a measure of the strength of a linear
relationship between two variables. always between –1 and 1, where either extreme denotes a perfect linear relationship and a correlation of zero denotes no linear relationship. Positive values of r denote a positive relationship, and negative values of r denote an inverse relationship 

Cox regression

A regression analysis procedure used in survival analysis with censored
data. The effects of independent variables are usually presented as risk ratios. Also called proportional hazards regression. 

dependent variable

In a regression analysis, the variable which is
predicted by the model. In linear regression, continuous. In logistic regression, it is dichotomous. In proportional hazards regression, it is a survival time. Also called response variable. 

dichotomous variable

A categorical variable having only two levels (e.g., presence or absence
of disease) 

explanatory variable

A variable which is used to predict the dependent variable in a regression
analysis. Also called independent variable. 

independent variable

A variable which is used to predict the dependent variable in a regression
analysis. Also called explanatory variable. 

indicator variable

An independent variable that takes on the values 0 or 1. For, example, to
indicate female gender, will be set to 0 for the males and 1 for the females. 

intercept

In a linear regression analysis, the mean of the dependent variable when
the independent variables are all set equal to 0. 

least squares

A procedure, based on minimizing the squared error, for estimating the
intercept and slopes in a linear regression analysis. 

linear regression

A statistical analysis that predicts a continuous dependent variable using
one or more independent variables based on a the equation of a line. 

logistic regression

A regression analysis procedure used to predict the value of a
dichotomous variable. The effects of independent variables are usually presented as odds ratios. 

multiple linear regression

A linear regression analysis using two or more independent variables.


multivariate analysis regression

A regression analysis (linear, logistic or proportional hazards) using two
or more independent variables. 

nonlinear

A relationship in which the scatterplot of a dependent variable and an
independent variable is not wellapproximated by a straight line. 

proportional hazards regression

A regression analysis procedure used in survival analysis with censored
data. The effects of independent variables are usually presented as risk ratios. Also called Cox regression. 

regression coefficient

An estimate of the intercept or slope in a regression analysis.


response variable

In a regression analysis, this is the variable which is
predicted by the model. In linear regression, the it is continuous. In logistic regression, it is dichotomous. In proportional hazards regression, it is a survival time. Also called dependent variable. 

scatterplot

A 2dimensional plot of a dependent variable (usually on the vertical
axis) and an independent variable (usually on the horizontal axis). Each point on the plot represents on subject from whom both variables are measured. 

simple linear regression

A linear regression analysis using one independent variable.


slope

In a linear regression analysis, the amount of change in the dependent
variable when the independent variable increases by 1 unit. 

univariate regression analysis

A regression analysis (linear, logistic or proportional hazards) using one
independent variable. 

central limit theorem

A mathematical result stating that for a sufficiently large sample size, the sampling distribution of the mean will be approximately normal regardless of the underlying distribution of the data.


confidence interval

The interval computed from sample data that has a given probability that the
unknown parameter is contained within the interval. The most common confidence interval is 95%. 

continuous scale

A scale used to measure a numerical characteristic in which fractional values
can occur (an example is body temperature). 

dataset

A collection of data organized into observations and variables.


discrete scale

A numerical scale using only whole numbers (an example is number of
pregnancies). 

distribution

The values of a characteristic or variable along with the frequency of their
occurrence. May be based on empirical observations or may be theoretical probability (e.g., normal, binomial, chisquare). 

histogram

A graphical display of a distribution, illustrating how frequently each value
occurs. 

mean

The most common measure of central tendency. In a sample, it is the
sum of the values divided by the number n in the sample. 

measures of central
location 
Index or summary numbers that describe the middle of a distribution. See
mean; median. 

measures of spread

Index or summary numbers that describe the spread of observations about the
mean. See range; standard deviation. 

median

A measure of central tendency. It is the middle observation; i.e., the one that
divides the distribution of values into two halves. It is also equal to the 50th percentile. 

mode

A measure of central tendency. The most common value(s) of a distribution.


nominal scale

The simplest scale of measurement. It is used for characteristics that have no
numerical values ( examples are race and gender). It is also called a categorical or qualitative scale. 

normal distribution

A symmetric, bellshaped probability distribution with mean µ and standard
deviation σ. If observations follow a normal distribution, the interval (µ ± 2×σ) contains 95% of the observations. It is also called the Gaussian distribution. 

ordinal scale

Used for characteristics that have an underlying order to their values; the
numbers used are arbitrary (an example is Apgar scores). 

parameter

An unknown summary value for an entire population. The purpose of a
statistical analysis is to estimate and make inferences about this. 

population

The entire collection of observations or subjects that have something in
common and to which conclusions are inferred. 

random sample

A subset of the population, usually obtained by random selection.


range

The difference between the largest and the smallest observation.


sampling
distribution 
The theoretical distribution of a statistic obtained from a random sample.


skewed distribution

A distribution in which there are a relatively small number of outlying
observations in one direction only. If the observations are small, the distribution is skewed to the left, or negatively skewed; if the observations are large, the distribution is skewed to the right, or positively skewed. 

standard deviation

The most common measure of dispersion or spread. It can be used with the
mean to describe the distribution of observations. It is the square root of the average of the squared deviations of the observations from their mean. 

standard error of the
mean 
The standard deviation of the mean in a large number of samples of size n.
A measure of how precisely a sample mean reflects the population mean and is used to calculate 95% confidence intervals around sample means. 

variance

The square of the standard deviation. It is a measure of dispersion in a
distribution of observations in a population or a sample. 

50th percentile

same as median


baseline analysis

In a decision analysis, the expected value of each strategy
calculated using best estimates of each probability and utility. 

chance node

Intermediate branch in decision tree from which chance events
occur. 

decision analysis

A formal, quantitative approach to examining tradeoffs when
making patientcare decisions. 

decision node

“Proximal” branch in decision tree that specifies clinical strategies
under consideration. 

decision tree

A diagram used in decision analysis to illustrate the possible
clinical options and outcomes. 

expected value

The relative value of clinical strategy, often expressed in qualityadjusted
lifeyears. 

falsenegative rate

Probability of a negative test result in a patient who has the disease
being tested for. Equal to 1 – sensitivity. 

falsepositive rate

Probability of a positive test result in a patient who is free of the
disease being tested for. Equal to 1 – specificity. 

fold back

In a decision analysis, the process of calculating expected values by
summing outcome utilities, each weighted by its probability of occurrence. 

gold standard test

A diagnostic test used to ascertain the true disease status when
estimating the sensitivity and specificity of another diagnostic test. 

negative predictive value

Probability a patient does not have the disease being tested for
following a negative diagnostic test. 

operating characteristics

The accuracy parameters of a diagnostic test: sensitivity, specificity,
positive predictive value and negative predictive value. 

positive predictive value
(PPV) 
Probability a patient has the disease being tested for following a
positive diagnostic test. 

posterior probability

An estimate of the probability a patient has a given disease after the
results of a diagnostic test are known. Also called posttest probability. 

posttest probability

An estimate of the probability a patient has a given disease after the
results of a diagnostic test are known. Also called posterior probability. 

pretest probability

An estimate of the probability a patient has a given disease prior to
the use of a diagnostic test. Also called prior probability. 

probability revision

The process of computing positive predictive value and negative
predictive value from the pretest probability. 

qualityadjusted lifeyears
(QALYs) 
Common measure of utility based on multiplying life expectancy by
a qualityadjustment factor. 

sensitivity

Probability of a positive test result in a patient who has the disease
being tested for. Also called truepositive rate. 

sensitivity analysis

Process of testing stability of a decision analysis by allowing input
probabilities and utilities to vary. 

specificity

Probability of a negative test result in a patient who is free of the
disease being tested for. Also called truenegative rate. 
true negative

terminal node

Most distal node in decision tree; represents a final clinical outcome
or condition. 

threshold value

In a decision analysis, the value of any input probability or utility
that makes the expected values of two clinical strategies equivalent. 

truenegative rate

Probability of a negative test result in a patient who is free of the
disease being tested for. Also called specificity. 

truepositive rate

Probability of a positive test result in a patient who has the disease
being tested for. Also called sensitivity. 

utility

The relative value of a clinical outcome in a decision analysis.


early detection

Any action that advances the time of awareness that a disease is present.


lead time

The increased time from diagnosis to death (or other outcome) due to earlier
diagnosis as opposed to later death. 

lengthbiased
sampling 
In a screening program, the tendency to detect indolent disease with a
relatively good prognosis. 

occult disease

Disease is detectable by testing but not evident by signs or symptoms. Also called subclinical disease.


preclinical
detection period 
The time interval when a disease can be found using screening techniques,
but before symptoms would bring it to clinical attention. 

primary prevention

An attempt to avoid any manifestations of disease. (Lowering cholesterol in
people without heart disease.) 

pseudodisease

Subclinical disease that would not become overt before the patient dies of
other causes, or which would never progress to clinical recognition. 

screening

The systematic examination of those who are apparently well (or who are
apparently free of the target disease) to identify and treat subclinical disease (or predictors of future disease). 

secondary
prevention 
An attempt to avoid progression of a disorder among individuals who
already have some signs (or symptoms) of the target disease (e.g., lowering colesterol in heart attack patients). 

subclinical disease

Disease is detectable by testing but not evident by signs or symptoms. Also called occult disease.


target disease

A disease or condition that is targeted by a screening program.


target population

A population selected for screening.


prior probability

An estimate of the probability a patient has a given disease prior to
the use of a diagnostic test. Also called pretest probability. 

blinding

The process of keeping clinical trial subjects and/or study personnel unaware
of the treatment assignments. Also used to describe the process of keeping study participants or personnel unaware of the hypotheses under study. 

casecontrol study

A research design in which subjects with a disease or outcome (cases) are
compared to subjects without the disease/outcome (controls). (Improperly called a retrospective study.) 

case report

An informal study in which the experience of a group of patients is
described, without a comparison group. Also called case series. 

case series

An informal study in which the experience of a group of patients is
described, without a comparison group. Also called case report. 

clinicbased

A study in which all subjects are derived from patients seen at a medical
facility. A hospitalbased study is an example. (Typically used with regard to a casecontrol study.) 

clinical trial

A formal intervention study, in which the investigators determine the
treatments or exposures of the subjects (usually by randomization). 

cohort study

A research design in which a defined group of subjects is followed over time
for the occurrence of events. (Contrast with crosssectional study.) Also called followup study. 

crosssectional
study 
A research design in which subjects are evaluated at only one timepoint.
(Contrast with cohort study.) 

doubleblind

A situation in which both subjects and investigators are unaware of the
subjects’ treatments or exposures. 

ecological study

An investigation in which the unit of analysis is a group. Examples include
correlation of trends over time in disease rates with trends in cigarette sales, or association of disease rates in different countries with cigarette sales. 

efficacy analysis

A statistical analysis of data from a randomized clinical trial in which the
outcome is evaluated according to the treatment actually received. This analysis procedure loses some of the advantages of randomization. (Contrast with intentiontotreat analysis). 

external validity

The ability of a study to apply to populations other than the one actually
studied. Also called generalizability. 

followup study

A research design in which a defined group of subjects is followed over time
for the occurrence of events. (Contrast with crosssectional study.) Also called cohort study. 

generalizability

The ability of a study to apply to populations other than the one actually
studied. Also called external validity. 

historical controls

A control group comprised of subjects whose past experience is contrasted
with those of currently observed subjects. Generally considered inferior to concurrent controls. 

information bias

A distortion caused by information provided by one group of subjects being
systematically different than that provided by another group. This potential problem is usually associated with casecontrol studies, in which case patients may provide systematically different information than controls. Also called response bias. 

intentiontotreat
analysis 
A statistical analysis of data from a randomized clinical trial in which
outcome is evaluated according to the randomized treatment group, regardless of what treatment was actually received. This analysis procedure makes full use of the advantages of randomization. (Contrast with efficacy analysis). 

internal validity

The ability of a study to reach a correct conclusion about the population
actually studied. 

intervention study

A study in which the investigators determine the exposures or treatments for
subjects. (Contrast with observational study.) 

observational study

A study in which the investigators do not determine the exposures or
treatments subjects experience. (Contrast with intervention study.) 

odds ratio

A type of relative risk; the only type of relative risk possible in casecontrol
studies. Calculated with a crossproduct ratio from a 2 × 2 table. 

placebo

A sham drug used in blinded studies to keep subjects and/or investigators
unaware of subjects’ treatment assignments. 

prospective study

An investigation in which the events studied occur during the time the
research is conducted. (Contrast with retrospective study.) 

randomization

A way of assigning treatments so that each subject has the same probability
of receiving a particular treatment. Makes treatment “independent” of the characteristics of the subjects, and thus effectively “prevents” confounding. 

response bias

A distortion caused by information provided by one group of subjects being
systematically different than that provided by another group. This potential problem is usually associated with casecontrol studies, in which case patients may provide systematically different information than controls. Also called information bias. 

retrospective study

An investigation in which all of the events studied have already occurred at
the time the research begins; existing records provide the data. (Contrast with prospective study.) 

selection bias

A bias that arises because of the selection of subjects in a study.


single blind

A situation in a clinical trial in which either the patient or the investigator
group is unaware of treatment assignment, but not both. The term is best used to describe the situation in which the investigators evaluating endpoints are unaware of treatment assignment. 