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Table 4 Survival analysis (Cox regression) of time to exiting the workforce (for any reason) during follow up (N = 11 529)a

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

Model Disease Presence Number Left workforce Cumulative proportion leaving workforce by 2 years HR (95 % CI) P value (Wald) Adjusted HR (95 % CI) P value (Wald)
1 Silicosis (grade 1/1+) No 11,053 2473 0.175 1.0 0.001 1.0 0.12
Yes 476 174 0.252 1.69 (1.34, 2.11)b   1.18 (0.96, 1.47)c  
TBd No 8512 1623 0.150 1.0 <0.001 1.0 <0.001
Yes 3017 1024 0.260 1.97 (1.77, 2.19)b   1.64 (1.47, 1.84)c  
  Interaction between silicosis and active/previous TB
2 Silicosis (grade 1/1+) and TBd No silicosis, no TB 8230 1525 0.147 1.0 <0.001 1.0 <0.001
Silicosis, no TB 282 98 0.233 1.97 (1.51, 2.57)b   1.54 (1.17, 2.04)e  
No silicosis, TB 2823 948 0.258 2.01 (1.79, 2.26)b   1.71 (1.51, 1.94)e  
Silicosis plus TB* 194 76 0.281 2.26 (1.84, 2.78)b   1.54 (1.20, 1.96)e  
  1. HR hazard ratio, CI confidence interval, TB tuberculosis
  2. aBased on reader I’s readings
  3. bAdjusted for clustering using robust standard errors
  4. cAdjusted for age category, years since first employed, country of origin, time spent underground, occupational level, silicosis/TB (active or previous) as appropriate, and clustering using robust standard errors. (n = 11 371)
  5. dTB defined as either previous or active TB at baseline by medical history or CXR by reader I
  6. eAdjusted for age category, years since first employed, country of origin, time spent underground, occupational level, and clustering using robust standard errors. (n = 11 371)
  7. *p-value for interaction between active/previous TB and silicosis <0.001 adjusting for clustering only, and p-value <0.001 from the fully adjusted model