Objective: This thesis aims to apply and compare selected regression methods with a lung fiber analysis dataset. Final results based on 19 cases will be compared to 2011 Marsh et al.’s analysis based on the first 15 cases.
Methods: Two research questions for the lung fiber dataset are: (1) is there a relationship between the lung fiber concentration of TAA and lung fiber concentration of AC? and (2) is there a relationship between the lung fiber concentration of TAA and duration of employment as a brake worker? Besides the substitution method, bivariate normal regression was used in the doubly left-censored situation in question 1, while the censored normal regression and regression modeling with count data were used in the situation with only the dependent variable subject to detection limits in question 2.
Result: (1) The estimate of the slopes between the log-scale of two lung concentrations (TAA vs AC) were 0.59, 0.57, 0.59 and 0.54 in the simple linear regression with substitution (DL, 0.5DL, DL/√2) and the bivariate normal regression, respectively. All of the slope estimates were statistically significant different from zero (p-value = 0.001, 0.003, 0.002 and 0.003). (2) The estimate of the slopes between the log-scale of the TAA lung fiber concentrations and DOE were 0.001, 0.014, 0.008, 0.020 and 0.030 in the simple linear regression with substitution (DL, 0.5DL, and DL/√2), censored normal regression and the negative binomial regression, respectively. All of the slope estimates were not statistically significant different from zero (p-value = 0.933, 0.486, 0.675, 0.390 and 0.439).
Conclusions: The consistent results from the substitution and other methods provide support for both a positive relationship between the lung concentration of TAA and AC and for no relationship between the lung concentration of TAA and DOE among 19 brake workers with mesothelioma. These findings are consistent with Marsh et al.’s findings in 2011 based on the first 15 cases. The public health significance is that the study results provide additional support for the conclusion that exposure to non-commercial amphibole asbestos, and not chrysotile, is related to the observed mesothelioma in brake workers. However, these conclusions need to be verified with a larger sample size
