Data processing and parametric and
nonparametric (chi-square, Wilcoxon rank
sum) tests of significance were performed
with SAS statistical software.21 Nonparametric
test results were used to support
parametric results when comparing length
of stay and hospital costs for helmeted
and unhelmeted motorcyclists, because
just a few individuals with very long stays
and higher costs can skew results. Logistic
regression analysis was performed with
EGRET epidemiologic software.22