What Influences the Association between Previous and Future Crashes among Cyclists? A Propensity Score Analysis

Background
It is known that experience of a previous crash is related to incidence of future crashes in a cohort of New Zealand cyclists. This paper investigated if the strength of such association differed by crash involvement propensity and by the need for medical care in the previous crash.
Methods
The Taupo Bicycle Study involved 2590 adult cyclists recruited in 2006 and followed over a median period of 4.6 years through linkage to four national databases. The crash involvement propensity was estimated using propensity scores based on the participants' demographic, cycling and residential characteristics. Cox regression modelling for repeated events was performed with multivariate and propensity score adjustments. Analyses were then stratified by quintiles of the propensity score.
Results
A total of 801 (31.0%) participants reported having experienced at least one bicycle crash in the twelve months prior to the baseline survey. They had a higher risk of experiencing crash events during follow-up (hazard ratio (HR): 1.43; 95% CI: 1.28, 1.60) but in the stratified analysis, this association was significant only in the highest two quintiles of the propensity score where the likelihood of having experienced a crash was more than 33%. The association was stronger for previous crashes that had received medical care (HR 1.63; 95% CI: 1.41, 1.88) compared to those that had not (HR 1.30; 95% CI: 1.14, 1.49).
Conclusions
Previous crash experience increased the risk of future crash involvement in high-risk cyclists and the association was stronger for previous crashes attended medically. What distinguishes the high risk group warrants closer investigation, and the findings indicate also that health service providers could play an important role in prevention of bicycle crash injuries.

背景
已有研究表明，新西兰自行车骑行者队列中，既往自行车碰撞事故经历与未来碰撞事故的发生率存在关联。本研究旨在探讨此类关联的强度是否因骑行者的碰撞参与倾向（crash involvement propensity）以及既往碰撞事故是否需要医疗救治而存在差异。

方法
陶波自行车研究（Taupo Bicycle Study）共纳入2006年招募的2590名成年骑行者，通过与四个国家级数据库关联开展随访，中位随访时长为4.6年。研究基于参与者的人口学、骑行及居住特征，利用倾向得分（propensity score）估算其碰撞参与倾向。采用多变量校正及倾向得分校正的重复事件Cox回归（Cox regression）模型进行分析，并按倾向得分的五分位数进行分层。

结果
共有801名（31.0%）参与者报告在基线调查前12个月内至少经历过1次自行车碰撞事故。该群体在随访期间发生碰撞事故的风险更高（风险比（Hazard Ratio, HR）：1.43；95%置信区间（Confidence Interval, CI）：1.28, 1.60），但分层分析显示，该关联仅在碰撞参与倾向最高的两个五分位数组（即既往碰撞发生概率超过33%的组别）中具有统计学意义。与未接受医疗救治的既往碰撞事故相比，既往因碰撞事故接受医疗救治的群体，其后续碰撞风险的关联强度更强（HR 1.63；95% CI：1.41, 1.88），未接受医疗救治组的风险比为1.30（95% CI：1.14, 1.49）。

结论
既往碰撞事故经历会提升高风险骑行者未来发生碰撞事故的风险，且既往碰撞事故接受过医疗救治的群体，其关联强度更为显著。明确高风险骑行群体的特征尚需进一步深入研究，同时本研究结果也提示，医疗服务提供者可在自行车碰撞损伤预防工作中发挥重要作用。