Supplementary Material for: Differing definitions of first-ever stroke influence incidence estimates more than trends: a study using linked administrative data

Introduction Researchers apply varying definitions when measuring stroke incidence using administrative data. We aimed to investigate the sensitivity of incidence estimates to varying definitions of stroke and lookback periods, and to provide updated incidence rates and trends for Western Australia (WA). Methods We used linked state-wide hospital and death data from 1985-2017 to identify incident strokes from 2005-2017. A standard definition was applied which included strokes coded as the principal hospital diagnosis or the underlying cause of death, with a 10-year lookback used to clear prevalent cases. Alternative definitions were compared against the standard definition by percentage difference in case numbers. Age-standardised incidence rates were calculated, and age- and sex-adjusted Poisson regression models used to estimate incidence trends. Results The standard definition with a 10-year lookback period captured 31,274 incident strokes. Capture increased by 19.3% when including secondary diagnoses, 4.1% when including nontraumatic subdural and extradural haemorrhage, and 8.1% when including associated causes of death. Excluding death records reduced capture by 11.1%. A 20-year lookback reduced over-ascertainment by 2.0% and a 1-year lookback increased capture by 13.3%. Incidence declined 0.6% annually (95% confidence interval -0.9, -0.3). Annual reductions were similar for most definitions except when death records were excluded (-0.1%, CI -0.4, 0.2) and with the shortest lookback periods (greatest annual reduction). Conclusion Stroke incidence has declined in WA. Differing methods of identifying stroke influence estimates of incidence to a greater extent than estimates of trends. Reductions in stroke incidence over time are primarily driven by declines in hospitalised stroke.

研究背景：研究者在利用行政数据测算脑卒中发病率时，采用的定义各不相同。本研究旨在探讨不同脑卒中定义与回溯期对发病率估算结果的敏感性，并为西澳大利亚州（Western Australia, WA）提供更新后的发病率数据与发病趋势。
研究方法：本研究使用1985年至2017年的全州住院与死亡关联数据，对2005年至2017年的新发脑卒中病例进行识别。采用标准定义：将编码为主要住院诊断或根本死亡原因的脑卒中纳入统计，并以10年回溯期清除既往病例。以病例数的百分比差异为指标，将不同替代定义与标准定义进行对比。计算年龄标化发病率，并采用年龄与性别校正的泊松回归模型估算发病趋势。
研究结果：采用10年回溯期的标准定义共检出31274例新发脑卒中病例。纳入次要诊断后检出率提升19.3%，纳入非创伤性硬膜下与硬膜外出血后提升4.1%，纳入相关死亡原因后提升8.1%。剔除死亡记录则使检出率降低11.1%。采用20年回溯期可使过度检出率降低2.0%，而1年回溯期则使检出率提升13.3%。发病率年均下降0.6%（95%置信区间：-0.9~-0.3）。多数定义下的年均降幅相近，但剔除死亡记录时仅下降0.1%（置信区间：-0.4~0.2），且回溯期最短的组别年均降幅最大。
研究结论：西澳大利亚州的脑卒中发病率呈下降趋势。不同的脑卒中识别方法对发病率估算结果的影响程度，大于对发病趋势估算的影响。脑卒中发病率随时间的下降主要归因于住院脑卒中病例的减少。