Numeracy and format influences comprehension of car seat recommendations

Child restraint systems (CRS) save lives in motor-vehicle crashes (MVCs) but incorrect use of CRS is common. One example is inappropriate transition between modes (e.g., rear-facing, forward-facing, and/or booster). Understanding manufacturer guidelines is therefore critical, but guidelines exceed consumer reading levels. The goal of this research is to examine the role of numeracy (i.e., math ability) in comprehension of CRS guidelines, which are highly numeric (e.g., relying on height, weight, age).

In an online experiment, 400 participants (who had previously completed an adaptive measure of numeracy) were shown one of six CRS usage diagrams based on major manufacturer's guidelines and answered questions about the appropriateness of CRS mode depending on child's height, weight, and age. We created two comprehension indices, one that allowed for two correct answers if both were appropriate and another with only the more conservative answer counting as correct. Participants also indicated perceived comprehension of the diagrams, knowledge of current CRS best practices, and prior CRS experience.

Average performance on CRS comprehension was 73% and 80% for the less and more conservative indices, respectively. Controlling for knowledge of CRS best practices and prior CRS experience, those higher in numeracy performed better in both perceived and actual comprehension. Perceived and actual comprehension also depended on diagram.

Our results suggest that CRS diagrams currently used by manufacturers are somewhat well-understood by consumers, but that there is room for improvement. The results for numeracy and the differences across diagrams suggest that reducing text and visual aids could improve comprehension. Although visualizations can help under certain circumstances, they were not shown to aid comprehension here.

Taken together, our results suggest that current manufacturer guidelines can be improved. They should be simplified by streamlining text and removing unnecessary visual aids, such as number lines.