Smallwood S, de Broe S. Sex ratio patterns in population estimates. Population Trends 2009; 137 (Autumn): 41-50.

The mid-year estimates (MYEs) resulting from the 2001 Census have a sex ratio pattern differing from patterns in previous estimates. Research has been undertaken to explain the observed sex ratio pattern in England and Wales (EW), covering recent censuses and
population estimates during the current intercensal period. The aims of this paper are to present some of the research explaining this sex ratio pattern and, secondly, suggest ways to prepare for the 2011 Census and beyond. A number of approaches have been taken to understand the drivers of the sex ratio pattern and provide evidence on plausibility. The Patient Register Data (PRD) was examined as a potential comparator. Sex ratios in other countries were compared with the EW sex ratio patterns. An accounting exercise for different explanatory scenarios around the remaining unexplained difference between estimates and 2001 Census was undertaken. Finally, demographic analyses examine trends in sex ratios among the migrant stock of the EW and foreign born populations to put into context the sex ratios in MYEs
following the 2001 Census.