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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.