| |
Change (%)
|
Sample size needed at baseline (80% power)
|
Expected power with sample size n = 2000 at baseline
|
|---|
|
Ct+
|
Ct-
|
Ct + (n = 300)
|
Ct- (n = 1700)
|
|---|
|
Scenario 1
|
10%
|
470
|
611
|
60%
|
> 99%
|
|
Scenario 2
|
15%
|
220
|
286
|
91%
|
> 99%
|
|
Scenario 3
|
20%
|
129
|
167
|
> 99%
|
> 99%
|
- Sample size and power calculations to detect a change in psychological determinants or sexual behaviour at six-month follow-up with at least 80% power, assuming 34% loss to follow-up in the chlamydia positives (Ct+) and 55% loss to follow-up in the chlamydia negatives (Ct-)
- Abbreviations: Ct+ chlamydia positive, Ct- chlamydia negative
