Monitoring the performance of breast screening programmes: use of indirect standardisation in evaluating the invasive cancer detection rate.

Close monitoring of data from individual programmes is required to evaluate the potential of the breast screening programme to reach the Health of the Nation target of 25% reduction in breast cancer mortality in the invited age group by the year 2000. This paper outlines the use of indirect age standardisation techniques to compare the performance of individual programmes in terms of their invasive cancer detection rates. Expected invasive cancer detection rates are calculated by applying data from the Swedish two county study to estimated England and Wales background incidence rates for different age strata. If the national programme overall meets these targets then the required mortality reduction should be achieved. The same method can be used by other (national) screening programmes by applying the relevant background incidence figures to produce internationally comparable data.