Using the information about housing characteristics and possession of household goods, an indicator of socioeconomic status (SES) was derived by the first component obtained by Principal Components Analysis (23) Only variables with factor loadings > 0.5 were maintained in the model. The variables included in the factor were: flooring material, ceiling material, availability of piped water,sanitary service, possession of refrigerator and washing machine as well as the number of electric appliances in the household: radio, TV, video player,telephone, and computer. The resulting standardized factor scores were divided into tertiles which were further used to construct SES status categories.