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 are the problems of the different methods of determining prevalence?

Answer 2

With point prevalence you need to consider whose data was and was not available when info was gathered. There may be self reporting errors, sensitivity and specificity of tests also need to be considered.

Question 3

What is incidence?

Answer 3

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

Question 4

What were the possible reasons for the association between circumcision and HIV (video)?

Answer 4

1. Overlaying of maps of tribes that practice circumcision and HIV rates (ecological study)
2. Experimentation - e.g. the deliberate infection of ‘live’ human foreskin
3. Case control and cohort ‘observational’ studies
4. Meta-analysis to calculate a combined estimate of effect from multiple studies