Effects of increasing child restraint use in reducing occupant injuries among children aged 0–5 years in Japan

Objectives:In Japan, child restraint use among pre-school children started to increase before compulsory child restraint use for children aged 0–5 years was introduced by legislation in April 2000. This study determined the effects of increased child restraint use in reducing motor vehicle occupant injuries among children aged 0–5 years.Methods:We obtained monthly police data of child vehicle occupant injuries from 1990 to 2009. We calculated monthly ratios of morbidity rates per population of children aged 0–5 years to those of children aged 6–9 years. Time trends of the morbidity rate ratios were analyzed using a joinpoint regression model to determine whether there were trend changes in child occupant injuries and when they occurred if there were trend changes.Results:The morbidity rate ratios showed a slightly increasing trend of 0.03% per month (95% confidence interval [CI], −0.02% to 0.09%) until the change-point in December 1997 (95% CI, July 1996 to January 1999), which then changed to a decreasing trend of −0.14% per month (95% CI, −0.16 to −0.11), with an overall trend change of −0.17% (95% CI, −0.23 to −0.11). No change-point was identified in or around April 2000 when compulsory restraint use was introduced.Conclusions:The present study used comparative indicators relative to age groups that were not covered by the legislation, and showed that a decrease in trend of occupant morbidity among children aged 0–5 years started before the introduction of compulsory restraint use. This change probably reflects the pre-legislative voluntary increase in child restraint use.

研究目的：在日本，2000年4月通过立法推行0~5岁儿童强制使用儿童约束装置之前，学龄前儿童的儿童约束装置使用率已呈上升趋势。本研究旨在明确儿童约束装置使用率提升对降低0~5岁儿童机动车乘员损伤的作用效果。
研究方法：本研究获取了1990年至2009年的月度儿童机动车乘员损伤警方统计数据。计算了0~5岁儿童与6~9岁儿童的人口发病率比值的月度数据。采用连接点回归（joinpoint regression）模型对发病率比值的时间趋势进行分析，以判断儿童乘员损伤是否存在趋势变化，并明确趋势变化发生的时间节点。
研究结果：1997年12月（95%置信区间[CI]：1996年7月至1999年1月）出现变化点之前，发病率比值呈现每月0.03%的小幅上升趋势（95%CI：-0.02%~0.09%）；变化点之后则转为每月-0.14%的下降趋势（95%CI：-0.16~-0.11），整体趋势变化幅度为-0.17%（95%CI：-0.23~-0.11）。在2000年4月强制儿童约束装置使用政策实施的时间点及其前后，未检测到变化点。
研究结论：本研究采用未受立法覆盖的年龄组作为对照指标，结果显示0~5岁儿童的乘员发病率趋势下降早在强制约束装置使用政策推行前便已出现。该趋势变化大概率反映了立法实施前民众自愿使用儿童约束装置的比例有所提升。