The imputation model of missing values included all dependent and independent variables of logistic models plus sampling design variables (primary sampling unit, stratum).
Primary sampling unit, stratum and individual weights were used to produce weighted point estimates, and variances were calculated using Taylor series linearization.
The primary sampling unit (PSU) was the parish and the stratification variables include the 9 strata (6 certainty primary frame sub-county unit strata plus three district strata).
The method accounts for the transition of sampling units among strata.
Multistage sampling is one of the applications of unequal probability sampling design where the selection of primary units within strata may be done with unequal probability.
Assuming no hidden biases, Rosenbaum and Rubin (1983) proved that when units within strata are homogeneous with respect to (hat{e}(Z)), then the treatment and control units in the same stratum will have the same distribution on Z.
In our analysis, we included all sub-Saharan countries where multiple Demographic and Health Surveys had been conducted between 1991 and 2006 and included explicit primary sampling units and strata.
Using the svy command in Stata (version 12), primary sampling units and strata for the data set were defined to account for the cluster-randomised design.
In the NHANES 2007 10 participants, we estimated the proportion of hypothyroidism within each class after correcting for the survey design variables (sampling weights, proportionality sampling units and strata) using the svy command in STATA software package.
