epidemiology question -

[ArchivalUser]

can u explain this !

A grp of 200 hypertensive pts and a comparable grp of 200 normotensive pts are enrolled into a longitudinal study to examine the effect of a diagnosis of hypertension on subsequent occurence of CHD . Study subjects are followed for 5 yrs . Final data are presented below .What is the attributable risk for hypertension ?

CHD No CHD Total
HTN 25 175 200

NO HTN 10 190 200

Total 35 365 400



A. 0.075
B. 2.5
C.2.7
D.0.125
E. Cannot be computed for this type of study.

[ArchivalUser]

Diego

For this Q you have to use the attributable risk formula:

(A/A+B) - (C/C+D) : but do remember that they can shift the order of the table so dont learn the "geography" of the table, learn the meaning. Generally A means positive positive, and D means negative negative.

So in this Q the calculation would be as follows:

25/25 +175 - 10/10+190
0.125 - 0.05 = 0.075

The think the answer is A.

[ArchivalUser]

Pinktie

It is A

[ArchivalUser]

Pinktie

The risk to get CHD is 10/200 = 0. 05 for control group.
The risk to get CHD is 25/200 = 0.125 for HTN group.

So the attributable risk for HTN is 0.125 - 0.05 = 0.075.

(In order to get pure risk for CHD from HTN, you have to subtract basal risk for CHD, which you get from the control group, from the risk that you get from HTN group)