Using funnel plots to explore variation in cancer mortality across primary care trusts in South-East England.

BACKGROUND: In 2004, the English government set a target to reduce the difference in cancer mortality in those aged under 75 between spearhead primary care trusts (PCTs) and all others by 6% in 2010. METHODS: We used mortality data for 2002-04 to calculate the age-standardized cancer mortality rates in 11 spearhead and 65 non-spearhead PCTs in South-East England. We calculated the ratio of each rate to that for England and Wales overall, and plotted these within funnel plots. RESULTS: Age-standardized cancer mortality ratios for males varied widely. The 11 spearhead PCTs had the highest mortality and six fell outside three standard deviations of the distribution of the funnel. Removing mortality due to lung cancer greatly reduced this variation and caused the outliers to shift down within the normal range. Ratios for females showed less variation, although those for spearheads were higher. One high outlier was unaffected by removing mortality due to lung cancer, other smoking-related cancers or breast cancer. CONCLUSION: Current variation in PCT cancer mortality is materially influenced by past patterns of smoking in men but less so in women. Effective smoking cessation policies should decrease inequalities in male cancer mortality, but will take time and be less effective in decreasing female inequalities.