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Table 3 Comparison of prevalence of silicosis by duration: 2000 study [12, 13] versus current study (ILO grade ≥1/1)

From: Trends in silicosis prevalence and the healthy worker effect among gold miners in South Africa: a prevalence study with follow up of employment status

2000 study (≥37 years of age) Current study (≥40 years of age)a
Duration yearsb N % Cases Silicosis prevalence % (95 % CI)c Duration yearsb N % Silicosis prevalence (reader I) % (n-cases) (95 % CI)c Silicosis prevalence (combined reading) %
≤20 179 14 7.8 (4.3, 12.8) ≤20 48 12.5 (6)(4.7, 25.2) 8.3
21+ 331 79 23.9 (19.4, 28.8) 21+ 182 20.3 (37)(14.7, 26.9) 14.4
Crude 510d 93 18.2 (15.0, 21.9) Overall 230 18.7 (43)(13.9, 24.3) 13.0
Adjustede    20.5     
  1. CI confidence interval. All figures rounded to one decimal
  2. aFor comparability, restricted to participants in this study from the same shaft and ≥40 years of age (N = 230)
  3. bDuration of exposure (2000 study), duration since first employment (current study)
  4. c95 % confidence intervals using binomial exact standard errors
  5. dNumbers used to derive Fig. 1 in 2000 study obtained from authors
  6. eStandardised to duration distribution of current study and the same shaft