DR Medhat MRCP

Case-control study
• Def :
- It`s a type of observational study in which the investigator select cases known to
have a disease and others who don`t have & obtains data regarding past H/O
exposure to possible etiological factors in both groups then he compares the rate
of exposure of two groups
- The validity of this type of study depends on the appropriate selection of the
control subjects
Simple 2X2 table used in Cohort and case-control study
Disease
Present
Absent
Present a
b
Exposure
Absent c
d
Total
a+b
c+d
Total a+c b+d n
127