Mortality rates for stroke in England from 1979 to 2004: trends, diagnostic precision, and artifacts

Stroke mortality appears to be declining more rapidly in the UK than in many other Western countries. To understand this apparent decline better, we studied trends in mortality in the UK using more detailed data than are routinely available.

Analysis of datasets that include both the underlying cause and all other mentioned causes of death (together, termed "all mentions"): the Oxford Record Linkage Study from 1979 to 2004 and English national data from 1996 to 2004.

Mortality rates based on underlying cause and based on all mentions showed similar downward trends. Mortality based on underlying cause alone misses about one quarter of all stroke-related deaths. Changes during the period in the national rules for selecting the underlying cause of death had a significant but fairly small effect on the trend. Overall, mortality fell by an average annual rate of 2.3% (95% confidence interval 2.1% to 2.5%) for stroke excluding subarachnoid hemorrhage; and by 2.1% (1.7% to 2.6%) per annum for subarachnoid hemorrhage. Coding of stroke as hemorrhagic, occlusive, or unspecified varied substantially across the study period. As a result, rates for hemorrhagic and occlusive stroke, affected by artifact, seemed to fall substantially in the first part of the study period and then leveled off.

Studies of stroke mortality should include all mentions as well as the certified underlying cause, otherwise the burden of stroke will be underestimated. Studies of stroke mortality that include strokes specified as hemorrhagic or occlusive, without also considering stroke overall, are likely to be misleading. Stroke mortality in the Oxford region halved between 1979 and 2004.