Understanding Uncertainty in School League Tables

In England, contextual value added (CVA) school performance tables are published annually by the government. These tables present statistical-model-based estimates of the educational effectiveness of schools, together with 95 per cent confidence intervals to communicate their statistical uncertainty. However, this information, particularly the notion of statistical uncertainty, is hard for users to understand. There is a real need to make school performance tables clearer. The media attempt to do this for the public by ranking schools in so-called ‘school league tables’; however, they invariably discard the 95 per cent confidence intervals and, in doing so, encourage the public to over-interpret differences in schools' ranks. In this paper, we explore a simulation method to produce simple graphical summaries of schools' ranks that clearly communicate their associated uncertainty.