Epidemiologic Study Designs - Health - Lecture Slides, Slides of Public Health

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Epidemiologic study

designs

Learning Objectives

• To understand the concepts of different

study designs

• To learn about the advantages and

disadvantages of several study designs

Epidemiologic study designs The basis for the lecture is the distinctionbetween descriptive epidemiology and analyticepidemiology Descriptive epidemiology:

seeks to measure the frequency in whichdiseases occur or collect descriptive data onpossible causal factors. Analytic epidemiology:

attempts to specify in more detail the causes ofa particular disease”

Epidemiologic study designs Types of Epidemiologic

Observational

Studies

based on:• type of sampling from population -

based on Exposure &/or Disease orneither

• temporal sequence of observation - one

time point, forward, backwards

Epidemiologic study designs Factors Important in Study DesignA. Specific, testable hypotheses - NOT a

fishing expedition

B. Biases

1. Internal validity2. External validity

Epidemiologic study designs

Study designs

Case series• Case Series report new diseases or

health related problems.

• They may provide some descriptive

data on exposures to potential causalfactors

Epidemiologic study designs Cross Sectional Studies

(contd)

-^

sample without knowledge ofExposure or Disease

-^

sample at one point in time

-^

Mostly prevalence studies/surveys

Epidemiologic study designs Cross Sectional Studies

(contd)

Advantages •^

Good design for hypothesis generation

-^

Can estimate overall and specific diseaseprevalence and sometimes rates

-^

Can estimate exposure proportions in thepopulation

-^

Can study multiple exposures or multipleoutcomes or diseases

Epidemiologic study designs Cross Sectional StudiesDisadvantages •^

Impractical for rare diseases

-^

Not a useful type of study for establishingcausal relationships

-^

Confounding is difficult to control

-^

No control over sample size for eachexposure by disease subclass

Epidemiologic study designs Cross Sectional StudiesDisadvantages •^

Problems with temporal sequence of data

-^

hard to decide when disease was actuallyacquired

-^

disease may cure the exposure

-^

miss diseases still in latent period

-^

recall of previous exposure may be faulty

Epidemiologic study designs Case-control studiesAdvantages•^

Best design for rare diseases

-^

Can be accomplished quickly since events ofinterest have already occurred

-^

Can study several potential exposures at thesame time

-^

Lends itself well to hospital-based studiesand outbreaks

Epidemiologic study designs Case-control studiesDisadvantages•^

Problems with temporal sequence of data

-^

Hard to decide when disease was actuallyacquired

-^

Disease may cure the exposure

-^

Miss diseases still in latent period

-^

Can’t calculate incidence, populationrelative risk or attributable risk

-^

HIGH potential for bias

Epidemiologic study designs

Cohort StudiesAdvantages •^

Can get best assessment of exposure and can dealwith changes in exposure

-^

May be only design if exposure needs to bemeasured directly

-^

Allows study of rare exposures

-^

Only way to get prospective information for rapidlyfatal diseases

-^

Good for establishing temporal sequence andnatural history of disease

-^

Can examine multiple outcomes linked to exposure -often find other effects than

Epidemiologic study designs Cohort StudiesAdvantages •^

Can estimate overall and specific disease rates, usuallyincidence

-^

Researcher selects, measures & records data

-^

Lower potential for bias than a case-control study - norecall and selection bias

-^

Results are considered more conclusive than results fromcase-control studies

-^

The longer a cohort study continues, the stronger it canbecome