Abstract:
Background: Recent UNAIDS guidelines recommend measuring concurrency 6 months
before the interview date, based on overlapping partnership dates. This has theoretical
advantages, but little is known about how well it can be measured in practice.
Methods: The assumptions underlying the UNAIDS measure were tested using data
from a sexual behaviour survey conducted in rural northern Malawi. All resident adults
aged 15–59 were eligible. Questions included self-reported concurrency and dates for
all marital and nonmarital partnerships in the past 12 months.
Results: A total of 6796 women and 5253 men were interviewed, 83 and 72% of those
eligible, respectively. Since few women reported multiple partners, detailed analysis was
restricted to men. Overall 19.2% [95% confidence interval (CI) 18.1–20.2] of men selfreported
concurrent relationships in the past year (almost all of those with more than one
partner). Using overlapping dates the estimate was 16.7% (15.7–17.7). Excluding
partnerships which tied on dates (making overlap uncertain) or restricting the analysis
to the three most recent partners gave similar results. TheUNAIDS 6-month measure was
12.0% (11.1–12.9), and current concurrency was 11.5% (10.6–12.4). The difference
between dates-based and self-reported 12-month measures was much larger for unmarried
men: 11.1% (9.7–12.4) self-reported; 7.1% (6.9–8.2) on dates. Polygyny (15% of
married men) and the longer duration of relationships stabilized the estimates for married
men.Nonmarital partnershipswere under-reported, particularly those starting longer ago.
Conclusions: The difficulties of recall of dates for relationships, and under-reporting
of partners lead to underestimation of concurrency using date-based measures. Selfreported
concurrency is much easier to measure and appears more complete.