At the beginning of the model, women are initialized with a number of living children who were born before the analytic timeframe begins. Modelling the number of existing children that women have at the start of the model allows for family planning preferences for ‘limiting’ or ‘spacing’ to be more appropriately captured.
We estimated the number of living children based on DHS data. We restricted our analysis to women who were sexually active (i.e. past age of sexual debut). Data were available for 3,046,522 women from 230 surveys in 71 countries.
We assumed that the number of living children follows a Poisson distribution. We fit hierarchical models to estimate the mean number of children by age and year, stratified by subgroup (urban/rural and level of education). We used upper middle income priors for high income countries due to lack of DHS data in high income countries.