Background: Child restraint systems (CRSs) significantly reduce risk of crash-related injury, however installation and use errors undermine their benefits. The National Highway Traffic Safety Administration (NHTSA) created the Ease of Use (EOU) rating system to help guide consumers and incentivize manufacturers to improve their products. The EOU rating system assigns one to five stars to four CRS features and overall. Our study assessed the relationship between EOU ratings and CRS installation and use errors documented in seat checks conducted by child passenger safety technicians (CPSTs).
Methods: We performed a secondary analysis of data from Safe Kids Illinois seat check records from 2015 through 2019 and EOU ratings from 2008 to 2020. Five types of errors were documented by CPSTs. Study authors (JYL and MLM) used a tiered system to match seat check model numbers to EOU ratings. We calculated chi-square statistics and performed logistic regression analyses to assess for EOU as a predictor of relevant CRS errors (e.g., tether errors for forward-facing CRSs).
Results: Our analyses included 2132 seat check observations, of which 217 (10.2%) were exact, 244 (10.5%) were probable, and 1671 (78.4%) were near matches via sorting and web search. Errors were most common for seat belts (70.7%) and least common for recline angle (36.9%). Star ratings for instructions, vehicle installation, and labels were associated with recline angle and seat belt errors. Star ratings for instructions, labels, and securing child were associated with harness errors. CRSs with 4-star and 5-star ratings had lower odds of errors for recline angle (Odds Ratio (OR) 0.62; 95% Confidence Interval (CI): 0.43, 0.89 and OR 0.31; 95% CI: 0.17, 0.56) lower anchors (OR 0.59; 95% CI 0.40, 0.89 and OR 0.38; 95% CI: 0.21, 0.68), and harness (OR 0.56; 95% CI: 0.40, 0.76 and OR 0.19; 95% CI: 0.10, 0.35) when compared with 1 and 2-star CRSs.
Conclusions: This study provides evidence in support of NHTSA's EOU ratings as predictors of some CRS installation and use errors among caregivers who obtain seat checks. A higher star rating may be helpful for caregivers when choosing a CRS that will yield lower installation errors.
Keywords: Child restraint systems; Ease of Use; installation errors; misuse.