Table 1

Description of studies included in the meta-analysis

Exposure categories
LocationStudy populationExposure measurement selected for the meta-analysisReferent categoryMid-term exposureLong term exposureConfounders considered in the statistical analysis or study designs
Case-control studies Duration of exposure to:
Cantor et al 19989Iowa (USA)732 cases 914 population controlsChlorinated surface water0 years1–39 years≥40 yearsAge, sex, study period, high risk occupation, and cigarettes.
Koivusalo et al 19988Finland1123 cases 1983 population controlsSubstantially mutagenic drinking water<15 years15–44 years≥45 yearsAge, socio economic status and smoking. Results stratified by sex.
King et al 199610Ontario (Canada)696 cases 1545 population controlsChlorinated surface water≤9 years10–34 years≥35 yearsAge, gender, log pack years of smoking, current smoking, education, and calorie intake.
McGeehin et al 199311Colorado (USA)327 cases 261 other cancer sites controlsChlorinated water0 years1–30 years>30 yearsCoffee consumption, smoking, tap water intake, family history of bladder cancer, sex, and medical history of bladder infection or kidney stones.
Vena et al 199315New York state (USA)351 cases 855 population controlsTap water0–49 years consuming 
 0–5 glasses/day0–49 years consuming 
 >10 glasses/day≥50 years consuming 
 >10 glasses/dayAge, education, cigarette smoking (pack years), sodium, carotene, and non-tap water. Only men.
Cantor et al 198713USA2855 cases 5258 population controlsChlorinated surface water0 years1–39 years≥40 yearsAge, sex, smoking habit, high risk occupation, population size of usual residence and reporting centre.
Cohort studies
Wilkins and Comstock 198114Washington County (USA)31000 study subjects, 81 bladder cancer casesDrinking water sourceDeep well usersChlorinated surface water usersAge, marital status, education, smoking history, frequency of church attendance, adequacy of housing, and persons per room.
Doyle et al 199716a Iowa USA28237 study subjects, 43 bladder cancer casesDrinking water source100% ground water sourceMixed surface-ground water100% surface water sourceAge, education, smoking status, pack years of smoking, physical activity, fruit and vegetable intake, total energy intake, body mass index, and waist to hip ratio