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92 Cards in this Set
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analytic crosssectional study

a study that tests one or more predetermined hypotheses about associations b/w exposure and outcome.


crosssectional study

an observational epidemiologic study in which exposure and outcome status are assessed simultaneously, that is, at the same point in time or during a brief period of time. Can be either descriptive or analytic, depending on whether or not a predetermined hypotheses is being tested.


analytic ecological study

a study that tests noe or more predetermined hypotheses about associations b/w exposure and outcome. Include multiplegroup comparison studies, timetrend stuides, and mixed studies.


ecological study

an observational epidemiologic study in which the units of analysis are groups of people versus individuals and where summary measures of exposure and outcome are used to determine associations. Can be descriptive or analytic.


chisquare test of independence

a statistical test of significance commonly used to determine if two nominal variables like exposure and outcome status are associated by compoaring observed and expected frequencies in a contigency table


coefficient of determination

in simple linear regression, the coefficient, this is the proportion of the variance in the dependent variable that is explained by the independent variable. Is measured by the square of the correlation coefficient (r). When there are multiple independent variables, as in multiple linear regression, this is the proportion of the variance in the dependent variable that is explained by all the independent variables considered simultaneously. This is measured by the square of the multiple correlation coefficient (R).


crude prevalence rate

the overall prevalence rate without regard to the exposure status of the group or population being studied


dependent variable

the outcome variable or effect that is influenced or predicted by other independent variables in a study. In epidemiology, this is typically outcome status.


exp

the exponential or e, which is the base used in natural logarithms. THe value of exp is approximately 2.7183. This expression is equivalent to e^x; thus, if the value is 2 you have e^2, or 2.7183^2.


independent variable

a variable that is expected to influence or predict the outcome variable in a study; in epidemiology, this is typically exposure status.


ln

the logarithm in the base e, or simply, the natural logarithm. in the expression (x)= Y, x is the natural logarithm of Y; that is, x is the power that e must be raised to get Y.


Pearson correlation coefficient

A statistical measure of the magnitude of the linear relationship b/w two continuous variables. r ranges from 1 to 1 , where 1 indicates a perfect inverse relationship, 0 indicates no relationship, and +1 indicates a perfect positive relationship.


prevalence rate difference

the difference between the prevalence rate in the exposed group and the prevalence rate in the unexposed group in an epidemiologic study


prevalence rate ratio

a measure of association commonly used in crosssectional studies. This (PRR) is the ratio of the prevalence rate in the exposed group to the prevalence rate in the unexposed group.


prevalence studies

a term sometimes used to refer to a crosssectional study because prevalence rates are the usual measures calculated.


regression equation

a mathematical expression that describes the relationship b/w a dependent and one or more independent variables. This allow investigators to predict the effect of the independent variables on the dpendent variable. Sometimes referred to as a prediction equation or a regression model.


regression line

the line that best describes the relationship b/w a dependent and an independent variable. This can be obtained by performing a simple linear regression analysis. Represents the line that best fits the date ina scatter plot.


scatter plot

the pattern of ponts that results when two quantitative variables are plotted on a graph. Each point formed by the intersection of the values of the two variables represents one unit in the analysis. The pattern of the points is indicative of the degree and direction of the relationship b/w the variablew.


a casecontrol study design in which pair matching is not used; that is, individual cases are not pair matched to individual controls during the selection process. Frequency matching, however, may be used.

unmatched casecontrol study


a statistical test used in the process of stratification to examine the probability that differences in stratumspecific measures of association are statisically different

test of heterogeneity


an odds ratio that is specific to a stratification subgroup and this is free of the confounding effect of the variable used in the stratification. This also has measures of association like the stratum=specific relative risk.

stratumspecific odds ratio


a procedure used in the nalysis phase of an epidemiologic study to control for confounding or to detect effect modification. This involves separating a sample into two or more subgroups according to specified levels of a third variable.

stratification


source population

the population from which the cases are selcted for a casecontrol study. In general, the controls also should be selected from this.


rare disease assumption

the assumption that the study outcome is rare. THis assumption normally is required when one uses the odds ratio to etimate the relative risk or ratio. A cumulative imcidence rate of less than 2 per 100 is good rul of thumb for what constitues a "rare" outcome.


a synonym for clinical significance

practical significance


an onogoing system that colects and registers all cases of a particular disease or class of diseases as they develop in a defined population.

populationbased disease registry


population based casecontrol study

a study in which the subjects are selected from the total or a representative sample of a defined population


subjects comprising the control group of a populationbased casecontrol study. These subjects are usually sleected randomly from the general population w/out the study disease.

population controls


multivariate methods

on of several statistical methods used to analyze the effects of more than one independent variable on a dependent variable.


a casecontrol study that uses pair mthcing, that is. individualcases are paired with individual controls during the selection process to control for potential confounding.

matched casecontrol study


an adjusted odds ratio that represents a type of wieghted average of stratumspecific odds raitos where the strata are the levels of a potential confounder and the wieghts depend on the number of observations in each stratum. This may be used when confounding is present but should not be used when effect modification is expected, since it can obscure the effect, which needs to be described and explained in a study.

MantelHaenszel relative risk


interaction

the combined effect of towo or more independent variables on a dependent variable. For example, this occurs when two risk factors together increase or decrease the magnitude of an outcome compared to only one of the factors. Synonymous with effect modification.


a study in which the subjects are selected among patients admitted to one or more clincial facilities, usually, but not necessarily, hospitals.

hospitalbased casecontrol study


hospital controls

subjects comprising the control group of a hospitalbeased casecontrol study. These are selected from hospitalized patients w/out the study disease.


a descriptive casecontrol study in which there is no predetermined hypothesis about the association b/w exposure and outcome. These can be used in identifigying potential risk factorsa nd possible causes of epidemics.

exploratory casecontrol study


effect modification

a real efect that occurs in a study when a third factor influences the direction or magnitude of a causal association b/w a study exposure and outcome. Also known as interaction.


cruse odds ratio

the overall odds ratio w.out regard to specific classificaitons variables, such as age, sex, or race/ethnicity.


clnicial significance

a level of satistical significance tht is meaningful from a public health or clinical point of view.


a procedure that keeps the investigators and/or the subjects unaware of subject classifications in analytic or experimental studies. the purposeof this is to minimize the bias that can result from kowing how the sujects are classified by exposure or outcome.

blinding


biomarker

a cellular or molecular indicator of exposure to an environmental agent, such as elevated liver enzymes or the presence of toxic residues in the blood, urine, hair, or other body specimens.


an odds ratio that has been statistically adjusted for one or more confounding factors.

adjusted odds ratio


cohort

a group of individuals who are folowed over time


external comparison group

in the context of a cohort study, this is a group outside the original cohort that serves as a control group for comparison purposes. Thse are often composed of general population samples in the same geographic are withsimlar demographic characterisitcs as the original cohort.


an epidemiologic study that comines features of retrospective and prospective cohort studies. This type of study indentifies a historical cohort and then folows it up into the future.

historical prospective cohort study


in the context of a cohort study, this represents those in the cohort who are unexposed to the study exposure.

internal comparison group


MantelHaenszel relative risk

an adjusted relative risk that represents a type of weigheted average of stratumspecific relative risks where the strata are the levels of a potential confounder and the weights depend on the number of observations in each stratum. THis may be used when confounding is present but should not be used when effect moidfication is expected, since it can obscure effect, which needs to be described and explained in a study.


a chisquare test that is used to determine the statistical significance of the rate ratio. It is known as this because the rate ratio is based on persontime incidence rates

persontime chisquare


placebo

an inert substance or treatment that is made to appear like the intervention in a randomized controlled trial. This has no known therapeutic effect.


placebo effect

the tendency for those receiving a treatment to experience beneficial effects even when the treatment has no known therapeutic value.


placebocontrolled trial

a randomized controlled trial in which the control group receives a placebo. Used for many drug trials.


randomization

the assignment of sujects to different study groups using random means. This assures that the subjects have the same probability of being assigned to any of the study groups.


a study in which the subjects are kept unaware of their group assignment, although the investigators are aware.

singleblinded study


stratified randomization

a randomization technique sometimes used in randomized contreolled trials hen the sample size is relatively small. This technique increases the probability that the experimental and control groups will be similar w/regard to the stratified factors. This involves three basic steps: spearation of the sample into appropriate strata, random allocation of sujects in each stratum into experimental and control groups, and compilation of the stratumspecific experimental and control groups into final experimental and control groups.


the writen plan and procedures to be followed in a study

study protocol


survival analysis

a method of analyzing data from studies involving folowup that is especially useful when the followup periods for subjects vary widely or when the sujects enter the study at different times. I this, one plots the time it took for each suject to develop the study outcome on a survival curve that provides data on the percent survival for any given time period, median survival time for a group, and other useful information.


tripleblinded study

a study in which the subjects, the investigators, and those analyzing the data are unaware of the subjects' group assignments.


washout period

a stage in a crossover design of a randomized controlled trial during which the effects of a previously applied intervention are believed to war off. Normally, the control condition is assigned after this.


an inanimate substance or object, such as food, water, bedding, or surgical equipment, that is capable of transmitting an agent of disease to a ssusceptible host. This serves as an intermidary in disease trnasmission, and the mechanism of transmission in considered indirect.

vehicle


vector

an animate source, such as a fly, mosquitio, or rodent, that is capable of transmitting an agent of disease to a susceptible host. This serves as an intermidary in disease transmission, and the mechanism of transmission is considered indirect. This may be infected with the disease organims or may be a mechanical carrier. Some limit the term to novertebrate species only, altough it is common practice to apply it to small vertebrate animals as well.


the residual effects of an intervention that can occur in a crossover study during the period after the intervention has been completed

carryover effects


crossover

a subject in the experimental group of a randomized controlled tial who does not complete the assigned intervention or a suject in the control group who seeks the inervention being tested. THese represent violations ofthe study protocol and can lead to erroneous conclusions about the fficacy of an intervention.


cancer cluster

the occurrence of a group of diagnostically distinct cancer cases in space or time whose distribution is believed not to be due to chance.


common source outbreak

an outbreak that results from the exposure of a susceptible group of people to a common agent of disease.


continuing source outbreak

a type of common source outbreak where the exposure to the common agent of disease is prolonged beyond a brieft period, and the exposure is not simulatneous among those exposed. Thise are expected to alst longer than the time range of the incubatin period of the disease because the exposure period is protracted, and not all are exposed at the same time.


crossover design

a variation of the traditional randomized controlled trial in which the intervention is applied at different times to each sujbect; this is, after a specified period of time the original experimental group beomces the control group, and the original control group becomes the experimental group.


a study in which neither the sujbects nor the investigators are a ware of the subjects' exposure status in prospectively designed studies or outcome status in retrospectively designed studies. The standard for randomized control trials.

doubleblinded study


disease cluster the occurrence of a group of cases, usually of a relatively uncommon diesase in space or time whose distribution is believed to be due to chance.

disease cluster


disease outbreak

an epidemic confined to a localized are, such as a town or within an institutional setting such as a daycare center or prison. This is often used synonymously with epidemic.


emerging infectious disease

an infectiouse disease previously unknown or virtually unknown in a population that has been increasing or threatening to increase in recent years.


effect size

the size of the association one would like to detect in a study if the association exists.


effective sample size

the remaining sample size after losses from a study


eligibilty criterea

the criterea used to define who is to be included and excluded from a study. In randomized controlled trials, the goal of the eligibility criteria is to optimize the conditions for successful testing of the efficacy of an intervention.


end point

a study outcome in a randomized control trial


evaluation study

a study designed to evaluate the impact of a healthrelated program, project, or campaign on a community.


epidemic curve

a graphic representation of the distribution of disease cses by time of onset in the form of a histogram. These are commonly used in the investigation of disease outbreaks and may provide clues to the source of the mode of trasmission of the disease.


exclusion criteria

the criteria used to define who is to be excluded from a study in something like a randomized control trial.


factorial design

a variation of the traditional randomized controlled trial which is intended to answer two or more resarch questions at the same time. In this type of study the sujbexts are randomized into experimental and control groups and then these groups are randomized again to test additional study hypotheses.


inclusion criteria

the criteria used to define who is to be included in a study for something like a randomized controlled trial


index case

the first case of a disease in a defined group to come to the attention of investigators during a disease outbreak. Ofthen this ist he ones who introduced the causative agent to the group


intentiontotreatanalysis

the nalysis of the results of a randomized controlled trial beased on the original assignments to experimental and control groups at the time of randomization, whether or not al lthe sujects complied with the study protocol.


intervention study

a synonym for experimental study. This name derives from the fact thatin eperimental studies the investigators intervene in the lives of the sujects by manipulating the ocnditions of exposure.


intermittent source outbreak

a common source outbreak where the exposure to the causative agent is irregular. This might occur, for exampke, when a contaminated food is served on different days over the course of a week.


metaanalysis

a method of statistically pooling the reulsts of several studies on the same topic in order to identify overall trends and to develop policy.


mixed outbreak

a combination fo common source and propagated outbreaks. This often begins w/a common source exposure that is followed by a persontoperson spread of disease


natural experiment

an unplanned type of experimental study. This is a relatively rare situation in nature where the levels of exposure to a presumed cause differ among a population in a way that is relatively unaffected by extraneous factors so that the situation resemebles a planned experiment.


passive surveillance

surveillance in which various health care providers are required by law to report certain diseases or conditions using prescribed methods designed by the agency responsible for surveillance


propagated outbreak

a progressive outbreak that is usually due to direct persontoperson transmission of the disease or by indeirect transmission through a vector.


point source outbreak

a type of common source outbreak where the duration of exposure to the common agent of disease is relatively brief and virtually simultaneous among the exposed. These are relatively shortlived and normally conclude w/in a time fram equal to the range of the incubation period of the disease.


public health surveillance

the ongoing systematic collection, analysis, interpretation, and dissemination of health data essential to the planning, implementation, and evaluation of public health practice


reemerging infectious disease

a once familiar infectious disease that was thought to be decreaing or disappearing in a population but is now on the rise.


sentinel event

a disease or condition that alerts public health authorities to a potential public health problem and that may require some type of public health response when reported


sentinel surveillance

surveillance that prearranges for certian health care providers to report all cases of certain predetermined diseases or conditions that may require a public health response. The reporting sources are usually a select sample of health care proivders that are likely to see the events an that have agreed to report them to the appropiate authorities.
