Study Design Flashcards by Kate Guiremand

goals of epidemiological studies

describe disease

identify associations

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a good study is:

scientifically sound

valid

precise

efficient

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descriptive study designs

not comparing groups

case reports
case series
cross-sectional descriptive studies

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analytical study designs

groups are compared

experimental
observational

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analytical study: experimental

clinical trials (treated/exposed)

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analytical study: observational

compare groups of populations- ecological

compare groups of individuals- cross-sectional analytical studies, case-control, cohort (prospective and retrospective)

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characteristics of descriptive studies

describe disease

no hypothesis is tested

no groups compared

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characteristics of analytical studies

determine if there is an association and if so the strength

designed to test hypothesis

always compares groups

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descriptive study: 1 subject

case report

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descriptive study: a few subjects (6-12)

case series

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descriptive study: lots of subjects (several dozen to hundreds)

descriptive cross sectional

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disadvantages of case reports and case series

small number of cases

findings are not generalizable to the population

strictly descriptive

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disadvantages of case reports and case series

small number of cases

findings are not generalizable to the population

strictly descriptive

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descriptive cross-sectional study

sample of population

estimate the amount and distribution of disease

measure of disease occurrence is usually prevalence

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steps of descriptive cross-sectional study

select subjects from the source population

measure the disease i each study subject

calculate the measure of disease occurrence

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advantages of descriptive cross-sectional study

can generalized to the population

fast and cheap

provide good descriptive or baseline data for future

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disadvantages of descriptive cross-sectional study

not good for causality

prevalence is of limited value

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what is an association

when one changes so does the other

exposure and outcome are dependent on one another

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outcome

a result or response, usually a disease or some other change in health status

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exposure

potential determinant of disease or health status

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T/F an exposure may increase, decrease, or have no effect at all

true

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determinant (risk factor)

once an exposure is shown to be associated with disease

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T/F analytical studies compare groups on the basis of either exposure or outcome

true

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T/F controls are essential for measuring the effect of exposure

true

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T/F controls are the reference group

true

how are analytical groups compared

exposure or outcome

observational studies

observes real life situations and draw inferences from them not given a treatment or exposure

experimental studies

investigator manipulates subjects subjects are selected and the allocated to receive a treatment or an exposure

selected

subjects selected because of their characteristics

allocated

assigned- experimental studies only located to receive a treatment or exposure in order to study the effect

subjects selected because..

represent a population exposure status outcome status

randomization

process of making something random each subject has an equal chance of being selected or allocated

sampling

subset of a population/group goal is to select sample to represents population or group studies

T/F in experimental studies subjects randomly allocated to groups

true

experimental studies as also known as

randomized control trials | clinical trials

T/F experimental studies can be done in the lab or field

true

advantages of experimental studies

may establish causality well-controlled studies are essential free of bias and confounding statistically powerful exposures and outcomes are clearly measured during the study

disadvantages of experimental studies

expensive and very narrow in scope not always ethical placebo effect loss of follow-up can be higher for some treatments

T/F in observational studies are selected to participate in the study and then classified into groups

true

what are 2 broad types of observational designs

populations | individuals

ecological study designs

compares groups of populations

T/F no measurements are made on individuals-all measured at a population level

true

steps in ecology study

select a sample of populations find population-level statistics on exposure and outcome for each population compare groups of populations

T/F exposure and outcome are not measured at an individual level, but at the population level

true

advantages of ecological study design

can be done quickly and inexpensively analysis and interpretation are relatively simple can assess a wide range of exposure levels

disadvantages of ecological study design

ecologic fallacy cannot detect subtle of complicated relationships

what is an ecologic fallacy

relationship observed at the population level may not hold true at the individual level

observational study on individuals

based on reason for selecting study subjects: represent a populations, have a certain outcome or exposure

analytical cross-section studies

individuals selected to represent a population only selected one

T/F analytical cross-section studies measure both exposure and outcome (usually at the same time)

true

advantages of analytical cross-sectional studies

can generalize to population fast and cheap provide good descriptive or baseline data for future studies

disadvantages of analytical cross sectional studies

not good for causality prevalence is limited (disease of long duration will have high prevalence even if incidence is low)

T/F diseases of short duration and high mortality will be under-represented in an analytical cross-sectional study

true prevalence is limited in nature

case-control studies

individuals are selected to represent outcome selected because of outcome status

T/F with case-control studies there is an association if the amount of exposure is different between the 2 outcome (disease) groups

true number of subjects with the exposure are counted in each outcome and compared

selection in case-control studies

selection of cases selection of controls

case definition

clearly describes and defines cases of the disease of interest

advantages of case control studies

short timeline can look at multiple risk factors at one time good for studying rare disease

disadvantages of case-control studies

poor selection of control can invalidate entire study depends on accurate assessment of exposures that happened in the past

cohort studies

selected to represent exposure groups used to study the effect of an exposure

what are they two types of cohort studies

prospective | retrospective

prospective cohort

forward in time subjects selected based on exposure status and then followed over time to see if they develop the outcome

measure of association for prospective cohort

relative risk

retrospective cohort

back in time selected based on exposure status, then outcome is determined from history, records, questionnaires, tests etc to determine if had/have outcome

measure of association for retrospective cohort

prevalence ratio (disease has already occurred)

advantages of prospective cohort studies

better to establish causality can look at multiple exposures at one time good for studying rare exposures

disadvantages of prospective cohort studies

can take a long time have to deal with changing study populations depends on accurate assessment of exposures and consistent assessment over time

advantages of retrospective cohort study

short timeline can look at multiple exposures at one time good for rare exposures

disadvantages of retrospective cohort studies

not as good for establishing causality poor selection of controls can invalidate the entire study depends upon accurate assessment of diseases that happened in past