Sampling Procedure
The survey was cross-sectional and targeted women and preschool children in two rural provinces in western and north-western Burkina Faso: the Sanguié province, in the Region of the Centre-Ouest; and the Sourou province, in the Region of the Boucle du Mouhoun. The target population consisted of women and preschool children because of their high micronutrient requirements due to their needs for reproduction and growth, respectively. Children aged 36 to 59 months were selected because at this age they were consuming family dishes, were unlikely to be breastfed, and were more likely to benefit from biofortification due to greater intake of sorghum than younger children. Mothers were recruited along with their children for convenience. One index child from the target age range was randomly selected from a household.
The sampling procedure was a multistage cluster selection process of 240 households in each province (five health areas per province × six clusters per area × eight households per cluster). At the first stage, health areas were randomly selected proportionally to their population size. Population sizes in health areas and villages were obtained from medical districts' records and were further checked for consistency by comparison of the data available from the National Census of 2006. At the next stage, six clusters (villages) were selected in each health area through the same proportional to size technique. Eligible households were identified in each village through a census of all households. Eligible households were those living permanently in the village and having a mother of a child aged 36 to 59 months who agreed to participate in the study. Among eligible households, the desirable number of households was then selected for the survey using a random number digits table. Out of 480 households having eligible woman and child pair that were selected for data collection, 478 actually took part in the survey. After analysis of food intakes, over- or under-reporters were excluded (24 women and 32 children). Out of 180 child-mother pairs selected for blood puncture, 166 women and 155 children were actually sampled.
