Standardized error severity score (ESS) ratings to quantify risk associated with child restraint system (CRS) and booster seat misuse

ABSTRACT

Objective: Although numerous research studies have reported high levels of error and misuse of child restraint systems (CRS) and booster seats in experimental and real-world scenarios, conclusions are limited because they provide little information regarding which installation issues pose the highest risk and thus should be targeted for change. Beneficial to legislating bodies and researchers alike would be a standardized, globally relevant assessment of the potential injury risk associated with more common forms of CRS and booster seat misuse, which could be applied with observed error frequency—for example, in car seat clinics or during prototype user testing—to better identify and characterize the installation issues of greatest risk to safety.

Methods: A group of 8 leading world experts in CRS and injury biomechanics, who were members of an international child safety project, estimated the potential injury severity associated with common forms of CRS and booster seat misuse. These injury risk error severity score (ESS) ratings were compiled and compared to scores from previous research that had used a similar procedure but with fewer respondents. To illustrate their application, and as part of a larger study examining CRS and booster seat labeling requirements, the new standardized ESS ratings were applied to objective installation performance data from 26 adult participants who installed a convertible (rear- vs. forward-facing) CRS and booster seat in a vehicle, and a child test dummy in the CRS and booster seat, using labels that only just met minimal regulatory requirements. The outcome measure, the risk priority number (RPN), represented the composite scores of injury risk and observed installation error frequency.

Results: Variability within the sample of ESS ratings in the present study was smaller than that generated in previous studies, indicating better agreement among experts on what constituted injury risk. Application of the new standardized ESS ratings to installation performance data revealed several areas of misuse of the CRS/booster seat associated with high potential injury risk.

Conclusions: Collectively, findings indicate that standardized ESS ratings are useful for estimating injury risk potential associated with real-world CRS and booster seat installation errors.

KEYWORDS:

• Child occupant safety
• biomechanics
• risk priority number (RPN)
• misuse mode and effects analysis (MMEA)

Acknowledgments

The authors thank the experts in injury biomechanics, occupant protection, and CRS design who volunteered their time to generate the ESS ratings: Kristy Arbogast, Katarina Bohman, Lotta Jakobsson, Kathy Klinich, Mike Lumley, Miriam Manary, Mats Svensson, and Suzanne Tylko. The authors also thank the three anonymous reviewers who provided thoughtful and constructive feedback on earlier versions of the article.

Funding

The authors acknowledge the support of Transport Canada's Road Safety Directorate, which provided funding for the project.