The UK government's health inequalities policy aims to improve the health of the poorest fastest.1^–3 Targets have been set to reduce health gaps between population groups,4 indicators have been identified for monitoring progress,1 and the new planning tool of health equity audit has been made mandatory for all primary care trusts.4 All these require the quantification and comparison of health gaps. Although we have many guidelines and directions on how to reduce socioeconomic inequalities in health, there has been little discussion or clear direction on how to quantify inequalities. This is important because the way health gaps are measured and compared affects the results. Lack of clarity about these distinctions has led to inconsistencies in the targets set and anomalies in how progress is assessed.