Background A decline in mortality rates from stroke has been observed in many industrialised countries in recent decades. We were interested in whether any of the observed decline in stroke, and its subtypes, might be artefactual rather than real. In particular, we wanted to determine whether any of the trends over time might be attributable to shifts in death certification practice between underlying cause and contributory cause, and/or shifts over time between certification of specific subtypes (haemorrhagic and ischaemic stroke) and stroke without specification of type.
Methods We analysed mortality data from the former Oxford NHS region 1979–2011. This has a longer run of multiple-cause coded mortality data than all-England mortality (though findings from the latter will also be shown). We calculated age-standardised rates, presented as mortality rates per million population, in each year from 1979–2011 and in grouped years for periods defined by national changes to the rules for selection of underlying cause (the rules changed in 1984, 1992 and 2001).
Results Mortality rates based on any mention of stroke on the death certificate, and on underlying cause, showed broadly similar trends. Mortality rates for each code for stroke – ischaemic, haemorrhagic and ‘unspecified’ – and for stroke overall fell at a broadly similar rate between 1979–1992. Thereafter, trends diverged. The average annual rate for mortality in men from ischaemic stroke in 2001–2011, at 72.7 per million, was 11% lower than that in 1993–2000 at 84.2. The corresponding rates for haemorrhagic stroke were 93.6 and 92.7, i.e. they did not fall at all. By contrast, the average annual rate for stroke ‘unspecified’ in men was 355.9 in 2001–11 which was 56% lower than the rate of 600.8 in 1993–2000. Stroke mortality, overall, fell from 768.1 to 504.5 between 1993–2000 and 2001–2011. In recent years, when national multiple-cause coding data were available, national trends were similar to those in Oxford in these respects. Rates for women will also be shown (they exhibited the same pattern).
Conclusion There have been substantial changes in certification practice with a shift in recent years away from specifying stroke type. Studies of trends in mortality from ischaemic stroke alone, or haemorrhagic stroke alone, without being put into the broader context of all stroke, would be seriously misleading. They would suggest a levelling off of the decline in ischaemic and haemorrhagic stroke mortality in recent years which is, in fact, an artefact of certification and coding practice.
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