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Table 2 Results of meta-analysis of all studies, silicotic studies and non-silicotic studies and subgroup analyses

From: Occupational exposure to silica dust and risk of lung cancer: an updated meta-analysis of epidemiological studies

Study design (effect measure) Number of studies Effect estimate P value of effect P value of heterogeneity, Q I2 P value Egger test
Cohort studies (SMR) 63 1.55 (1.38–1.75) 5.68E-13 <0.0001 96.18 0.02
Cohort studies (SIR) 19 1.68 (1.45–1.96) 1.36E-11 4.59E-08 74.51 0.24
Cohort studies (RR) 1 1.65 (1.13–2.40) 0.01 1   0.72
Case-control mortality studies (OR) 5 1.82 (1.25–2.66) 0.0017 0.1070 51.17 0.51
Case-control incidence studies (OR) 9 1.34 (1.24–1.46) <0.0001 0.2075 0 0.46
Case-control studies (MOR) 3 1.69 (1.26–2.26) <0.0001 <0.0001 86.70 1.00
Proportional mortality studies (PMR) 2 1.10 (0.89–1.36) 0.38 0.10 62.02 1.00
Silicotic studies (SMR) 24 2.32 (1.91–2.81) <0.0001 <0.0001 94.34 -
Silicotic studies (SIR) 4 2.49 (1.87–3.33) <0.0001 0.377 25.04 -
Silicotic studies (OR) 3 2.56 (1.84–3.57) <0.0001 0.345 2.65 -
Silicotic studies (MOR) 3 1.88 (1.31–2.71) 0.0006 <0.0001 86.98 -
Non-silicotic studies (SMR) 4 1.78 (1.07–2.96) 0.027 0.013 74.37 -
Non-silicotic studies (SIR) 2 1.18 (0.86–1.62) 0.292 0.192 41.21 -
Subgroup analysis of SMR studies
Year of publication
  ≤ 1990 16 2.37 (1.76–3.19) 1.24E-08 2.92E-94 95.58 0.35
 1991–2000 21 1.44 (1.21–1.71) 2.97E-05 1.25E-30 89.89 0.16
  > 2000 26 1.30 (1.16–1.46) 1.05E-05 9.98E-49 93.50 0.60
Industry
 Mine 18 1.48 (1.18–1.86) 0.00 4.73E-59 97.17 0.18
 Foundry 4 1.51 (0.99–2.29) 0.05 0.02 86.53 0.75
 Pottery 7 1.14 (1.05–1.23) 0.00 0.27 0.02 1.00
 Cement 4 0.87 (0.42–1.82) 0.71 <0.0001 84.87 0.75
 Construction 2 1.55 (1.31–1.82) 1.94E-07 0.66 0.00 1.00
 Stone & granite 8 1.32 (1.15–1.50) 6.24E-05 0.01 65.17 0.72
 Mixed 19 2.03 (1.61–2.56) 1.68E-09   96.95 0.73
Country
 Europe 26 1.54 (1.25–1.89) 4.95E-05 4.09E-33 95.70 0.13
 USA 15 1.24 (1.12–1.38) 6.24E-05 5.32E-07 79.80 0.06
 Canada 5 2.14 (1.46–3.13) 9.27E-05 2.34E-32 95.70 0.82
 Australia 2 1.73 (1.51–1.98) 7.65E-15 0.26 19.61 1.00
 Asia 14 1.74 (1.27–2.39) <0.0001   97.56 0.75
Occupational confounders
 Absent 13 1.32 (1.14–1.54) <0.0001 1.79E-13 87.15 0.06
 Present 30 1.35 (1.17–1.57) 7.28E-05 7.37E-55 94.47 0.55
Reported measure adjusted for smoking
 Not adjusted 61 1.55 (1.37–1.75) 4.16E-12   96.37 0.02
 Adjusted 2 1.83 (1.51–2.22) 7.23E-10 0.43 0.00 1.00
NOS score
 1–3 6 2.56 (1.57–4.19) 0.00 2.35E-65 96.18 1.00
 4–6 35 1.57 (1.36–1.82) 9.02E-10 1.68E-80 93.07 0.45
 7–9 15 1.24 (1.01–1.52) 0.042025 1.56E-44 97.23 0.17
Cumulative Silica Dust Exposure (CSDE) (mg/m3years)
 0 < CSDE ≤ 0.83 5 1.19 (1.02–1.39) 0.02 0.02 68.92 0.23
 0.83 < CSDE ≤ 3.9 5 1.27 (0.89–1.82) 0.19 1.04E-24 97.57 0.48
 3.9 < CSDE ≤ 8.35 4 1.33 (0.94–1.87) 0.10 2.97E-10 91.94 0.75
 CSDE > 8.35 5 1.36 (0.87–2.13) 0.18 1.15E-21 96.33 0.82
Subgroup analysis of SIR studies
Year of publication
 ≤ 1990 4 2.32 (1.50–3.58) <0.0001 0.07 64.63 0.75
 1991–2000 6 1.77 (1.17–2.69) 0.01 5.07E-09 85.81 0.47
  > 2000 9 1.54 (1.40–1.70) 8.29E-18 0.41 17.30 1.00
Industry
 Mine 2 1.67 (1.32–2.13) 2.55E-05 0.07 69.32 1.00
 Foundry 4 1.40 (1.23–1.58) 2.67E-07 0.52 7.15 0.33
 Pottery 1 2.34 (0.62–8.84) 0.21 1   0.33
 Cement 3 1.34 (1.01–1.76) 0.04 0.43 12.61 1.00
 Construction 1 1.50 (1.26–1.79) 5.04E-06 1   1.00
 Granite 3 1.94 (1.55–2.44) 1.33E-08 0.93 0.00 1.00
 Mixed 5 2.13 (1.18–3.87) 0.01 4.08E-05 85.96 0.82
Country
 Europe 13 1.78 (1.48–2.14) 1.16E-09 9.18E-08 77.40 0.13
 Canada 2 1.42 (0.52–3.93) 0.49 0.05 74.77 1.00
 Australia 1 1.89 (1.57–2.28) 2.26E-11 1   1.00
 Asia 3 1.38 (1.10–1.73) <0.0001 0.28 6.72 1.00
Occupational confounders
 Absent 3 1.94 (1.55–2.44) 1.33E-08 0.93 0.00 1.00
 Present 12 1.57 (1.32–1.87) 4.14E-07 4.45E-08 80.28 0.64
NOS grading
 1–3 3 1.99 (1.19–3.30) 0.01 0.95 0.00 1.00
 4–6 11 1.55 (1.28–1.87) 5.74E-06 2.36E-08 82.02 0.76
 7–9 1 1.61 (1.21–2.14) <0.001 1   0.76
  1. I 2 variability due to heterogeneity; R2, SMR standardized mortality ratio, SIR standardized incidence ratio OR odds ratio, MOR mortality odds ratio, PMR proportional mortality ratio, NOS Newcastle-Ottawa scale