Discordance between Age and Size Based Criteria of Child Passenger Restraint Appropriateness

<p><b>Objectives</b></p> <p>In this study we sought to accomplish the following objectives: 1) to calculate the percentage of children considered appropriately restrained across eight criteria of increasing restrictiveness; 2) to examine agreement between age- and size-based appropriateness criteria; 3) to assess for changes in the percentage of children considered appropriately restrained by the eight criteria between 2011 (shortly after updates to United States (U.S.) guidelines) and 2015.</p> <p><b>Methods</b></p> <p>Data from two cross-sectional surveys of 928 parents of children younger than 12 years old (n = 591 in 2011, n = 337 in 2015) were analyzed in 2017. Child age, weight, and height were measured at an emergency department visit and used to determine if the parent-reported child passenger restraint was considered appropriate according to eight criteria. Age-based criteria were derived from Michigan law and U.S. guidelines. Weight, height, and size-based criteria were derived from typical restraints available in the U.S. in 2007 and 2011. The percent appropriate restraint use was calculated for each criterion. The kappa statistic was used to measure agreement between criteria. Change in appropriateness from 2011 to 2015 was assessed with chi-square statistics.</p> <p><b>Results</b></p> <p>Percent appropriate restraint use varied from a low of 19% for higher weight limits in 2011 to a high of 91% for Michigan law in 2015. Agreement between criteria was slight to moderate. The lowest kappa was for Michigan law and higher weight limits in 2011 (κ = 0.06) and highest for U.S. guidelines and lower weight limits in 2011 (κ = 0.60). Percent appropriate restraint use was higher in 2015 than 2011 for the following criteria: U.S. guidelines (74% vs. 58%, p<0.001), lower weight (57% vs. 47%, p = 0.005), higher weight (25% vs. 19%, p = 0.03), higher height (39% vs. 26%, p<0.001) and higher size (42% vs. 30%, p = 0.001).</p> <p><b>Conclusions</b></p> <p>The percent of children considered to be using an appropriate restraint varied substantially across criteria. Aligning the definition of appropriate restraint use with current U.S. guidelines would increase consistency in reporting results from studies of child passenger safety in the U.S. Potential explanations for the increased percentage of children considered appropriately restrained between 2011 and 2015 include adoption of the updated U.S. guidelines and the use of child passenger restraints with higher weight and height limits.</p>