4、Case-Control Study

Case-Control Study

Learning Objectives

“A primary goal is to reach the same conclusions in a retrospective (casecontrol) study as would have obtained from a forward (cohort) study, if one had been done.”Source: Mantel, N, Haenszel,W. Statistical aspects of the analysis of data from retrospective studies of disease. J Natl Cancer Inst. 1959; 22:719-48

Example of the Ideal Design

But we cannot achieve the counterfactual ideal

Population of HBV infected

Follow-up: 2000-2015

Measure Liver Ca Incidence

Different subjects Measure Liver Ca Incidence

Population of HBV non-infected

Follow-up: 2000-2015

Desirable situations for a Case-Control Study

SampleControls =

Sample of the denominator

Representative with

regard to exposure

2 by 2 table

illNot ill

a

ExposedExposed

(unprotected)

illbExposed(unprotected)healthy

c

Not exposedNot exposed

(protected)

illdNot exposed(protected)healthy

Case-control study

ill

exposedhealthy

Not

exposed

Time

Case-control StudyCase-control Studiekrank exponiert gesund

illExposed Not exposed

Healthy 20

a c

b d

nicht exponiert

10

Zeit

10

60

a/c 20 x 60 OR= b/d= ad= 10 x 10 cb

= 12

95%-confidence Interval (CI)= 3,93 - 38,02 2

ad bc T2

N1 N 0 M1 M 0

p= 0,0000002

Example: Passive smoking and Breast Cancer

Fundamental conditions for the validity of this

case-control design

Solution:

Case Definition

Control definition

Why not use hospital controls?

Have you ever been exposed?

Unexposed= never active, never passive

Case-control study design

Results of the study

Interpretation of the Odds Ratio Alternatively:

(in what situation?)

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