2.13. Statistical analysis
Mean exposure levels for both pollutants, and levels of all studied biomarkers, were compared in the Bangkok and Chon- buri students by way of the Mann–Whitney U-testusing the SPSS v.10 software package. A Pearson correlation was used to evaluate the association between personal exposure levels and levels of urinary metabolites. A P-value ≤0.05 was considered as statistically significant.