Question

Researchers are interested in the relationship between depression and bacterial vaginosis among expecting mothers enrolled in a case-control study. Suppose the following computerized printout reports a summary table for the relationship.

Table of dep by bv
dep	bv
	_case	control	Total
_exposed	35	89	124
nonexposed	45	503	548
Total	80	592	672

Calculate the prevalence of the exposure in the investigation.

Answer 1

	cases	controls	total
exposed	35	89	124
nonexposed	45	503	548
Total	80	592	672

Prevalence is the number or proportion of subjects/individuals with some exposure to depression in a point in time or period of time, in our case.

prevalence of the exposure = no of cases when exposed to depression/ total no. of individuals in the study = 35/672 = 0.0521

we could also, find the prevalence ratio = prevalence of the disease with exposure/ prevalence of the disease without exposure.

= (35/672)/(45/672)= 35/45= 0.778

which tells us, that prevalence of the disease with exposure is less than the prevalence of the disease without exposure.