Understanding and Appraising Evidence

Question 1

What is prevalence?

Answer 1

Number of cases of a disease within a defined population measured at a specific point in time. Prevalent cases include both new (incident) and existing cases

Question 2

What is incidence?

Answer 2

Overall incidence = new cases in cohort/total number in cohort

Question 3

What is relative risk?

Answer 3

The incidence in the exposed group divided by the incidence in the non-exposed group.

Question 4

What needs to be ruled out before a causal relationship can be considered?

Answer 4

Chance (especially in small studies?)
Bias (can be minimised with careful study design and aggregating data from different types of study)
Is the sample representative/generalizable/big enough?
Confounding

Question 5

Should men be circumcised as part of HIV prevention?

Answer 5

• Yes as it could reduce HIV rates in both sexes

- Circumcised men can still get HIV so it shouldn’t be a lone strategy

Question 6

What does the evidence suggest of the link between HIV and circumcision?

Answer 6

• There is compelling evidence that male circumcision reduces the risk of heterosexually acquired HIV infection in men by approximately 60%.