Dry cleaners, USA: SMRs* for selected cancers by time since first employment in PCE-using shops and duration of employment in PCE-using shops
| Site | Time <20 years | Time <20 years | Time 20+ years | Time 20+ years | p Value† | |
| Duration <5 years | Duration 5+ years | Duration <5 years | Duration 5+ years | By time | By duration | |
| All | 24 deaths | 32 deaths | 136 deaths | 130 deaths | <0.001 | 0.52 |
| 0.61‡ (0.42 to 0.85) | 1.16 (0.84 to 1.55) | 1.43§ (1.24 to 1.65) | 1.33§ (1.14 to 1.54) | |||
| Tongue | 0 | 0 | 4 | 1 | NP | 0.25 |
| 0.00 | 0.00 | 11.33§ (3.87 to 25.93) | 2.84 (0.15 to 13.49) | |||
| Oesophagus | 0 | 0 | 5 | 11 | NP | 0.085 |
| 0.00 | 0.00 | 2.16 (0.85 to 4.54) | 4.78§ (2.68 to 7.91) | |||
| Intestine | 2 | 4 | 17 | 13 | 0.20 | 0.52 |
| 0.59 (0.10 to 1.86) | 1.64 (0.56 to 3.76) | 1.75‡ (1.12 to 2.63) | 1.22 (0.72 to 1.94) | |||
| Lung | 4 | 6 | 42 | 25 | 0.009 | 0.35 |
| 0.63 (0.21 to 1.44) | 1.27 (0.55 to 2.50) | 1.75§ (1.33 to 2.26) | 1.08 (0.75 to 1.51) | |||
| Cervix | 2 | 4 | 4 | 3 | 0.23 | 0.66 |
| 0.84 (0.15 to 2.66) | 2.63 (0.90 to 6.03) | 2.75 (0.94 to 6.30) | 2.08 (0.57 to 5.38) | |||
| Bladder | 0 | 0 | 1 | 9 | NP | 0.12 |
| 0.00 | 0.00 | 0.53 (0.03 to 2.52) | 4.08§ (2.13 to 7.12) | |||
* Approximate 90% CIs on SMRs calculated using exact Poisson distribution or the formulae of Breslow and Day.20
† The effect of time since first employment is based on the confidence interval for a directly adjusted standardised rate ratio comparing the 20+ group with the <20 group, ignoring employment duration. The effect of employment duration is based on the confidence interval for a directly adjusted standardised rate ratio comparing the 5+ group with the <5 group, ignoring time since first employment. NP indicates that the test could not be performed due to zero deaths in the lower category.
‡ 95% CI excludes the null value (1.0).
§ 99% CI excludes the null value (1.0).
PCE, perchloroethylene; SMR, standardised mortality ratio; CI, confidence interval.