Table 1

Description of studies included in the meta-analysis

				Exposure categories
	Location	Study population	Exposure measurement selected for the meta-analysis	Referent category	Mid-term exposure	Long term exposure	Confounders considered in the statistical analysis or study designs
Case-control studies			Duration of exposure to:
Cantor et al 1998⁹	Iowa (USA)	732 cases 914 population controls	Chlorinated surface water	0 years	1–39 years	≥40 years	Age, sex, study period, high risk occupation, and cigarettes.
Koivusalo et al 1998⁸	Finland	1123 cases 1983 population controls	Substantially mutagenic drinking water	<15 years	15–44 years	≥45 years	Age, socio economic status and smoking. Results stratified by sex.
King et al 1996¹⁰	Ontario (Canada)	696 cases 1545 population controls	Chlorinated surface water	≤9 years	10–34 years	≥35 years	Age, gender, log pack years of smoking, current smoking, education, and calorie intake.
McGeehin et al 1993¹¹	Colorado (USA)	327 cases 261 other cancer sites controls	Chlorinated water	0 years	1–30 years	>30 years	Coffee consumption, smoking, tap water intake, family history of bladder cancer, sex, and medical history of bladder infection or kidney stones.
Vena et al 1993¹⁵	New York state (USA)	351 cases 855 population controls	Tap water	0–49 years consuming   0–5 glasses/day	0–49 years consuming   >10 glasses/day	≥50 years consuming   >10 glasses/day	Age, education, cigarette smoking (pack years), sodium, carotene, and non-tap water. Only men.
Cantor et al 1987¹³	USA	2855 cases 5258 population controls	Chlorinated surface water	0 years	1–39 years	≥40 years	Age, sex, smoking habit, high risk occupation, population size of usual residence and reporting centre.
Cohort studies
Wilkins and Comstock 1981¹⁴	Washington County (USA)	31000 study subjects, 81 bladder cancer cases	Drinking water source	Deep well users		Chlorinated surface water users	Age, marital status, education, smoking history, frequency of church attendance, adequacy of housing, and persons per room.
Doyle et al 1997^16a Iowa USA		28237 study subjects, 43 bladder cancer cases	Drinking water source	100% ground water source	Mixed surface-ground water	100% surface water source	Age, education, smoking status, pack years of smoking, physical activity, fruit and vegetable intake, total energy intake, body mass index, and waist to hip ratio