Table 2

Pooled estimates of bladder cancer among hairdressers: stratified analysis

Stratified analysis Set of studies	No of studies	Pooled estimators		Homogeneity
Stratified analysis Set of studies	No of studies	SRR	95% CI	χ²	p Value
All studies	42	1.34	1.21 to 1.48	39.88	0.52
Gender
Data for female hairdressers16 18 23 24 26 28 31 33 37 38 40 43 44 49 51 53 55	17	1.25	1.05 to 1.50	15.55	0.48
Data for male hairdressers15–17 19 22 24–29 32–40 42 44 46–49 51–56	32	1.52	1.34 to 1.72	36.14	0.24
Study period^*
Ascertainment of cases < 197915 17 18 27–34 36 38–40 43 47 49 53	19	1.37	1.19 to 1.58	12.35	0.83
Ascertainment of cases 1980–198916 19 22 35 37 42 44 46 48 52 54	11	1.24	1.00 to 1.53	7.15	0.71
Ascertainment of cases > 199020 21 23–25 45 50 51 55 56	10	1.42	1.16 to 1.75	13.82	0.13
Study area^†
USA/Canada15–24 26–28 31 32 34 37 41 47 51	20	1.28	1.08 to 1.52	10.69	0.93
Europe/Nordic countries25 29 30 33–35 38–40 42–46 48–50 52–54 56	20	1.34	1.19 to 1.52	21.20	0.33
Adjusted data
Adjusted for smoking15 17–25 27 34 35 37 39 41 45 46 48 50 54–56	23	1.35	1.13 to 1.61	28.81	0.19
No adjustment16 26 28–33 36 38 40 42–44 47 49 51–53	19	1.33	1.18 to 1.50	14.05	0.78
Study quality level
High quality15–25	11	1.35	1.03 to 1.77	4.77	0.91
Moderate quality26–56	31	1.34	1.20 to 1.49	35.11	0.24

↵* Two studies26 41 were excluded because study period was not presented in the original study.
↵† Two studies from New Zealand35 55 were excluded from this analysis.