Figure 1.

Spline regression analysis of amyotrophic lateral sclerosis (ALS) risk for increasing particulate matter (PM₁₀) exposure for both annual median and maximum levels using 10th, 50th, and 90th percentile distribution (A,C) or fixed categories ((B): 5, 10 and 20 µg/m³; (D): 10, 20 and 50 µg/m³) as cutpoints. The black line indicates the odds ratio for ALS risk; the gray area indicates 95% confidence limits; the reference line is at 1.0; black spikes indicate the distribution of participant PM₁₀ levels.