Table 2

Exposure-response estimates of silica and onset of radiographic opacities (ILO≥1/0 or large opacities) by Poisson regression restricting observation to cumulative exposure <10 mg/m³.y (radiographic opacities: ILO≥1/0, n=60, person–years=15659)

Model*	a_i Estimate	Change in (−2lnl)	RR at 1.0 mg/m³.y†	RR at mean exposure‡	RR at maximum exposure
*Based on median (mean) date of first positive film by three (or two) B readers. Stratifying on age (13 levels), calendar time (nine levels), ethnicity (Hispanics v other) and time since first observed (three levels). Cumulative exposures were unlagged and classified in 50 levels together with unexposed level, a₁ and a₂ are estimated parameters in two parameter models; †Estimate for cumulative exposure of 1.0 mg/m³.y; ‡Evaluated at mean and maximum cumulative exposures of cases of lung disease other than cancer in full study population.
Log-linear	0.2596	25.99	1.30	3.66	77.55
Log-square root	1.045	32.54	2.84	10.35	72.10
Log-quadratic:
a₁	0.8191	35.22	2.13	13.07	0.04
a₂	−0.0601
Power	1.311	33.72	2.48	10.48	43.45
Linear relative rate	4.928	35.18	5.93	25.64	83.59
Shape:
a₁	6.095	35.27	7.10	27.37	84.64
a₂	0.9333