The nonparametric Kruskal-Wallis test was used to test for statistical
differences among the three age groups. If this test showed significant
differences, multiple Wilcoxon Rank Sum tests were
performed to compare two groups at a time. These nonparametric tests
make no assumptions about the underlying distribution of the data
being compared.
p 
.05 was used as the level for statistical
significance
in detecting
univariate group differences. Statistical analysis
was performed using SAS software release 6.12 (Cary, North Carolina).
Group results are reported as mean 
standard error.