Tests for trend are based on the p-value for the lead variable categorized into quartiles.
Bone lead was categorized into quartiles separately for each lead PD model; thus, the numbers of cases and controls by quartile differ across models.
We used linear regression to assess the association between lead biomarkers, categorized into quintiles, and continuous tremor scores in our primary analyses.
Using blood lead levels categorized as < 5, 5 to < 10, and ≥ 10 μg/dL, we determined the relative risk of mortality from all causes, cancer, and cardiovascular disease through Cox proportional hazard regression analysis.
Using blood lead concentration categorized as < 8 μg/dL (0.384 μmol/L), and ≥ 8 μg/dL (0.384 μmol/L), we determined the relative risk of mortality from all cause, and cause-specific mortality, through Cox proportional hazards regression analysis.
For GFR, the group with the next highest exposure level [urinary cadmium, 0.75 1 μg cadmium/L; mean, 0.86 μg cadmium/L = 1.0 μg cadmium/g creatinine; adjusted for age, BMI, and blood lead (each categorized into four groups) and for NSAID use (into 0 or 1); Figure 1C] differed from the lowest level.
Blood lead levels were categorized as < 5, 5 to < 10, and ≥ 10 μg/dL.
Serum cotinine and blood lead levels were categorized into quintiles and quartiles, respectively, using weighted percentages.
Poverty index, ferritin, and lead levels were categorized into terciles based on the sample distribution.
Log-transformed blood lead was either categorized into quartiles or treated as a continuous variable in a cubic regression spline.
