Is the reported estimate for the concentration threshold value for respirable quartz really plausible?

摘要

The study is based on a large-scale cohort of workers in the porcelain industry. The analysis yielded merely 40 incident silicosis cases with nearly 130,000 person-years of observation. In contrast, five parameters are fitted in the corresponding Cox model on the basis of this small number of cases, not counting the offset parameter . On the basis of the small number of cases, one would expect large estimation errors, but astonishingly the 95% confidence interval for the estimate of the threshold value t was rather narrow (0.16 to 0.30 mg/m3). Unfortunately, the authors did not present the estimates for the other model parameters. In particular, the corresponding estimates for the slope with respect to the exposure concentration (parameter "b" in equation [3](1)) are needed to validate the results on other data sets.