There was substantial truncation of the values of some of the scores. Over half of the scores for hypersecretion were scored at zero, potentially resulting in biased effect estimates from standard ordinary least squares (OLS) regression. Therefore, the regression models were estimated using both OLS and Tobit regression models where the scores are treated as left-censored at zero. The OLS and Tobit regressions were conducted using statistical software (PROC REG and PROC LIFEREG, respectively, in SAS/STAT; Cary, NC).
Summary information on individuals included in the study is presented in Table 2. Individuals who had lived in the high pollution area were, on average, somewhat younger and less likely to smoke than those who had lived in the low air pollution area. The smokers from the high pollution area, however, smoked somewhat more pack-years. As also can be seen in Table 2, the mean scores of the five histopathologic parameters were higher for those who had lived in the high pollution area vs those who had lived in the in the low pollution area. For anthracosis, inflammation, and wall thickness, the difference was 40%. For hypersecretion, the difference was more than double, and for the gland/wall ratio, the difference was small and only marginally statistically significant. buy risnia 2 mg
Table 3 presents a comparison of mean and median scores of the five histopathologic parameters (proximal and distal parenchyma) for smokers and nonsmokers who had lived in the high and low pollution areas. For both smokers and nonsmokers, the mean and median scores for each of the five parameters are consistently higher for those from the high pollution area. In Figure 1, individual and mean scores for the four histopathologic parameters are also presented for smokers and nonsmokers from the high and low pollution areas. While the mean values of these four parameters were consistently higher for those from the high pollution area, this figure also demonstrates that there was substantial variability across individuals within groups, especially for anthracosis.
Table 3—Mean and Median Levels of the Histopathologic Variables for Smokers and Nonsmokers Exposed to Levels of Pollution
Figure 1. Mean and individual values of the morphologic parameter scores for smokers (smk) and nonsmokers (non smk) who lived in low (L) and high (H) air pollution levels.
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