Table 5

Comparison of HIV seroprevalence estimates based on standard probit models and models accounting for sample selection under various scenarios (Zewditu Memorial Hospital, Addis Ababa, 2003–04)

Scenario


Test of Heckman modela

Post-test counseling is required

Post-test counseling is optional

E(HIV% – Probit)

17.7

(16.4 – 19.1)

17.8

(16.6–19.1)

21.4

(20.2–22.7)

E(HIV% – Heckman)

23.1

(21.7 – 24.4)

23.4

(22.1–24.7)

23.7

(22.4–25.0)

Observed HIV%

22.2

(19.9 – 24.4)

unknown

unknown

Sample

Consent groups A and B

All consent groups

All consent groups

Assumption

HIV status in consent group B is unobserved

HIV status in consent groups B and C is unobserved

HIV status in consent group C is unobserved

LR test H0:ρ = 0

p < .01

p < .01

p = .07


Notes: 95%- CI are reported between brackets. Using dummies for admission diagnosis rather than the likelihood of infection in these regressions hardly changes the estimated prevalence rates though one of the selection models did not converge.

a In the first column, we assume that HIV status in consent group B is unknown, and compare the ordinary Probit and Heckman selection model estimate with the true or observed value of HIV prevalence.

Reniers et al. BMC Public Health 2009 9:163   doi:10.1186/1471-2458-9-163

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