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The reliability and validity of the age-sex register as a population denominator in general practice.

I report evidence which raises doubts about the reliability and validity of age-sex registers as true population denominators in general practice in the UK. These have potentially disturbing implications for the interpretation of data based on the presumed precision of age-sex registers. I am undertaking a prospective study to identify and quantify sources of inaccuracy to try to establish a method of estimating the true population at risk and its true age-sex characteristics. This would greatly enhance the utility of the age-sex register as the most valuable tool in general-practice research.