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Table 10 Methods and findings from studies comparing population-based and sentinel surveillance antenatal HIV prevalence in India.

From: A population-based study of human immunodeficiency virus in south India reveals major differences from sentinel surveillance-based estimates

Location [Reference] Data collection year(s) Sampling approach Participation rate Sample size (n) Number of HIV-positive Population HIV prevalence as % (95% CI)* Power of sample size to detect difference from antenatal HIV prevalence at 95% confidence level† Comments
Tamil Nadu: 3 districts [7] 1998 90 rural & urban clusters selected using probability proportional to size; selected households from each cluster invited for medical camp; first 25 adults 15–45 years old from each cluster who came to camp included in study 82.5% for selected households; not mentioned for eligible individuals 1981 34 Age & sex adjusted: 1.80 (0.89–2.71) 17% to detect 20% difference from 1% antenatal HIV prevalence Selection bias likely due to medical camp sampling approach, making interpretation difficult;
Grossly underpowered for reliable comparison with antenatal HIV prevalence
Tamil Nadu: 1 rural sub-district, 1 urban town [8] 1999–2000 120 rural & urban clusters selected using probability proportional to size; 15–40 years old people from randomly selected households included in study 90.9% of 3–40-year-olds; not mentioned for eligible 15–40-year-olds 2870 29 Crude: 1.01 (0.44–1.58) 21% to detect 20% difference from 1% antenatal HIV prevalence Grossly underpowered for reliable comparison with antenatal HIV prevalence
Karnataka: 1 district [31,32] 2003 10 villages and 20 urban blocks selected with cluster sampling using probability proportional to size; 15–49-year-olds included in study; further details not published 59.8% of 6700 eligible 15–49-year-olds 4008 118 Crude: 2.94 (2.12–3.76) 50% to detect 20% difference from 2.6% antenatal HIV prevalence Poor participation rate makes interpretation difficult;
Underpowered for reliable comparison with antenatal HIV prevalence
Andhra Pradesh: 1 district [This study] 2004–2005 5 subdistricts selected to represent strata in district, from which 66 rural & urban clusters selected randomly; 15–49-year-olds from randomly selected households included in study 91.2% of 13838 eligible 15–49-year-olds 12617 241 Age, sex & rural-urban adjusted: 1.72 (1.35–2.09) 93% to detect 20% difference from 3% antenatal HIV prevalence Adequately powered for reliable comparison with antenatal HIV prevalence
  1. *Although the two Tamil Nadu papers reported adjusting for cluster design effect, the magnitude of this effect was not reported, and the confidence intervals reported in both these papers are implausibly narrow even if no design effect were considered (cluster design effect widens the confidence interval). The Karnataka study did not report design effect information. Because specific details about cluster design effect in these studies were not available, we used the cluster design effect of 2.44 from our study to calculate the confidence intervals for the other studies, using standard statistical methods [12,24]
  2. †Power calculated assuming cluster design effect of 2.44 for all studies, using standard statistical methods [12,13]; sentinel surveillance antenatal HIV prevalence for comparison as reported in each study.