Data analysis
We used a linear mixed-effects model to examine the effect of bubble wrap on body pressure distribution. Period, sequence, and mattress were entered into the model as fixed effects, and subjects nested within the sequence were entered as random effects. A Bonferroni correction was performed to compare the main effects among different mattress conditions. Age, sex, and BMI were entered into the model as covariates to control for potential confounding factors. In our study, a 