Table 1

Abstracted study information and risk estimates for bladder cancer from the individual studies and assessment of study quality

Quality level: high	Study design	Study area	Study period^*	Study population	Hairdressers:		Main risk estimate^† (95% CI or p value)	Grading criteria
Quality level: high	Study design	Study area	Study period^*	Study population	Cases	Gender	Main risk estimate^† (95% CI or p value)	1	2	3	4	5	6
Schoenberg et al15	Case-c.	USA	1978	1916	12	M	1.27 (0.59 to 2.73)^§	***	***	***	**	***	***
Schumacher et al16	Case-c.	USA	1980	1294	2	F	0.45 (0.01 to 4.08)	*******	*******	*******	*******	*******	*******
						M	0.69 (0.01 to 8.59)
Silverman et al17	Case-c.	USA	1977	5974	7	M	2.80 (0.70 to 11.60)^§	*******	*******	*******	**	*******	*******
Silverman et al18	Case-c.	USA	1977	1918	17	F	1.40 (0.70 to 2.90)^§	*******	*******	*******	**	*******	*******
Siemiatycki et al19	Case-c.	Canada	1982	2897	4	M	1.00 (0.30 to 2.90)^§	***	*******	*******	*******	*******	*******
Teschke et al20	Case-c.	Canada	1990	244	3	F/M	3.2 (0.20 to 179.00)^§	***	*******	*******	*******	*******	*******
Gago-Dominguez et al21	Case-c.	USA	1992	3028	20	F/M	1.5 (0.70 to 3.20)^§	*******	*******	*******	*******	*******	*******
Zheng et al22	Case-c.	USA	1988	2736	5	M	1.8 (0.40 to 8.00)^§	***	*******	*******	*******	*******	*******
Colt et al23	Case-c.	USA	1997	331	4	F	2.1 (0.50 to 8.00)^§	***	**	*******	*******	*******	*******
Gaertner et al24	Case-c.	Canada	1996	3734	8	M	3.42 (1.09 to 10.80)^§	***	**	*******	*******	*******	*******
					6	F	0.75 (0.28 to 2.01)^§
Samanic et al25	Case-c.	Spain	1999	2079	12	M	1.24 (0.51 to 3.01)^§	***	*******	**	*******	*******	*******

Quality level: Moderate	Study design	Study area	Study period^*	Study pop.	Hairdressers:		Main risk estimate^† (95% CI or p value)	Grading criteria
Quality level: Moderate	Study design	Study area	Study period^*	Study pop.	Cases	Gender	Main risk estimate^† (95% CI or p value)	1	2	3	4	5	6
Viadana et al27	Case-c.	USA	1960	35 428	5	M	1.49 p>0.05^§	*******	*	*	*******	*******	*
Howe et al28	Case-c.	Canada	1975	1264	3	M	4.04^¶	***	***	***	^*	***	***
					2	F	6.03^¶
Alderson29	Cohort	England	1970	504	7	M	1.23 p=0.33	***	***	***	^*	^*	***
Cartwright 30	Case-c.	England	1979	2329	4	F/M	0.9 (0.30 to 3.20)	***	^*	**	^*	**	***
Teta et al31	Cohort	USA	1956	11 845	14	F	1.6 (0.74 to 2.27)	*******	*******	*******	*******	*	*******
Dubrow and Wegman32	Cohort	USA	1972	16 629	4	M	1.16 p<0.001	***	***	***	^*	^*	***
Guberan et al33	Cohort	Switzerland	1962	1380	10	M	2.56 (1.39 to 4.35)	***	***	***	**	^*	***
					2	F	2.00^‡
Morrison34	Case-c.	Boston	1977	2388	7	M	1.00 (0.00 to 2.60)^§	***	*******	*******	*	*******	**
		Manchester			2	M	NP
		Nagoya			1	M	NP
Vineis and Magnani35	Case-c.	Italy	1981	1108	9	M	0.90 (0.40 to 2.30)^§	***	^*	^*	**	***	***
Pearce and Howard36	Cohort	New Zealand	1976	5356	2	M	17.84 (2.00 to 64.40)	***	*******	*******	*	*	*******
Risch et al37	Case-c.	Canada	1987	1618	9	F	1.44 (0.22 to 11.80)^§	***	**	***	**	***	***
					11	M	0.65 (0.13 to 2.98)^§
Lynge and Thygesen38	Cohort	Denmark	1975	14 371	7	F	1.76 (0.71 to 3.36)	*******	^*	***	^*	^*	***
					41	M	2.05 (1.51 to 2.78)
Steineck et al39	Case-c.	Sweden	1968	541	1	M	0.40 (0.00 to 4.70)^§	*******	*******	*******	*	*******	*******
Skov et al40	Cohort	Norway	1972	6505	23	M	1.50 (1.00 to 2.30)	***	^*	***	^*	^*	***
					11	F	1.50 (0.80 to 2.80)
		Sweden	1970	23 464	54	M	1.50 (1.10 to 1.90)
					6	F	0.40 (0.20 to 1.00)
		Finland	1975	9566	0	M	1.67 (NP)
					3	F	1.70 (0.40 to 5.10)
		Total		39 535	97	F/M	1.30^‡
Burns and Swanson41	Case-c.	USA	NP	6139	11	F/M	0.90 (0.40 to 1.90)^§	***	***	^*	***	***	**
Kunze et al42	Case-c.	Germany	1981	1062	10	M	1.70 (0.60 to 4.50)	***	*	**	**	**	*
Pukkala et al43	Cohort	Finland	1979	247	1	F	0.40 (0.01 to 2.24)	*******	*******	*******	*	*	*******
Trögner44	Case-c.	Germany	1987	546	2	M	1.00 (1.14 to 7.10)	***	*	**	**	*******	*******
					0	F	0.25 (NP)
Bolm-Audorff et al45	Case-c.	Germany	1990	600	7	F/M	6.48 (1.15 to 36.61)^§	***	*******	**	**	*******	**
Cordier et al46	Case-c.	France	1986	1316	5	M	1.49 p>0.05^§	*******	*	**	**	*******	*******
Burnett et al47	Cohort	USA	1975	133 560	6	M	1.42 (NP)	***	^*	***	**	^*	***
Golka et al48	Case-c.	Germany	1986	824	3	M	0.73 (0.15 to 3.48)^§	***	^*	**	**	***	**
Skov and Lynge49	Cohort	Denmark	1979	4337	67	M	1.58 (1.24 to 2.01)	***	^*	***	^*	^*	^*
					12	F	1.23 (0.64 to 2.15)
Sorahan et al50	Case-c.	England	1992	2938	11	F/M	1.70 (0.74 to 3.89)^§	***	**	***	*	*******	*******
Lamba et al51	Cohort	USA	2001	9495	6	M	0.59 (0.27 to 1.31)	***	^*	**	**	^*	***
					88	F	1.36 (1.10 to 1.68)
Bouchardy et al52	Cohort	Switzerland	1987	58 134	24	M	1.50 (1.00 to 2.20)	***	***	^*	^*	^*	**
Czene et al53	Cohort	Sweden	1979	45 690	51	F	1.09 (0.81 to 1.43)	***	***	***	***	^*	***
					87	M	1.22 (0.98 to 1.51)
Ji et al54	Cohort	Sweden	1984	24 041	88	M	1.10 (0.88 to 1.34)^§	***	*	*******	*******	**	*******
Dryson et al55	Case-c.	New Zealand	2003	684	6	F/M	9.15 (1.60 to 52.22)^§	***	*	*******	**	*******	*******
					2	M	5.41^‡
					4	F	9.95 (1.37 to 72.21)
Golka et al56	Case-c.	Germany	1993	492	4	M	4.9 (0.85 to 28.39)^§	***	**	**	**	***	***

Case-c, case-control design; cohort, retrospective cohort design including registry data; M, male; F, female; Grading criteria, 1 (clearly stated aim), 2 (response rate / trace rate), 3 (comparability of subjects), 4 (elevation of exposure), 5 (adequate statistical analysis and confounding), 6 (discussion of limitations and generalisability), NP, not presented; bold, statistically significant.
↵* Mean year of ascertainment of bladder cancer cases.
↵† Effect estimates used for the overall meta-analysis, stratified data not presented in table.
↵‡ Calculated by data given by the original study.
↵§ Smoking-adjusted (unadjusted data not given).
↵¶ If extended data are provided but the count in the exposed control group was 0, the risk estimator and SE were calculated by adding a correction of 0.5 events in order to include the study in the meta-analysis as suggested by the Cochrane Collaboration.11