Table 4.

Summary results of the meta-analysis of benzene exposure and non-Hodgkins lymphoma (NHL) and meta-analysis of refinery work and NHL

	Fixed effects				Shore CI			Random effects			Heterogeneity
	N	RR	CIlow	CIup	RR	CIlow	CIup	RR	CIlow	CIup	χ 2	p	I2 (%)
Benzene and NHL
All studies	22	1.22	1.03	1.46	1.22	1.02	1.47	1.23	1.02	1.48	22.8	0.36	8
Case-control studies	16	1.23	1.00	1.50	1.23	0.99	1.52	1.21	0.97	1.51	16.8	0.33	12
Cohort studies	6	1.21	0.86	1.71	1.21	0.83	1.77	1.34	0.86	2.09	5.9	0.31	16
High exposure studies
All	13	1.49	1.15	1.92	1.49	1.12	1.97	1.49	1.09	2.04	14.9	0.25	20
No self-reported data	6	2.12	1.11	4.02	na*	na	na	na	na	na	2.1	0.83	0
Healthy worker effect adjusted
Cohort studies	6	1.22	0.89	1.67	1.22	0.80	1.85	1.54	0.92	2.59	8.6	0.13	42
All studies (cohort and case control)	22	1.22	1.03	1.45	1.22	1.02	1.48	1.24	1.01	1.51	25.4	0.23	17
All high exposure studies	13	1.53	1.19	1.96	1.53	1.15	2.03	1.55	1.14	2.12	15.8	0.20	24
High exposure, no self-reported data	6	2.26	1.29	3.97	na*	na	na	na	na	na	2.1	0.83	0
Refinery work and NHL
All studies (cohort only)	21	1.21	1.06	1.38	1.21	1.00	1.46	1.21	0.97	1.53	40.0	<0.01	50
High exposure studies†	14	1.30	1.04	1.62	1.30	0.90	1.88	1.18	0.79	1.77	35.3	<0.01	63
Healthy worker effect adjusted
All studies	21	1.42	1.25	1.62	1.42	1.19	1.69	1.44	1.16	1.78	37.6	0.01	47
All high exposure studies†	14	1.51	1.22	1.88	1.51	1.07	2.14	1.37	0.94	2.01	33.1	0.01	47

Abbreviations: CI_low, lower 95% CI; CI_up, upper 95% CI; p, p value for the heterogeneity statistic; RR, summary relative risk estimate; χ², chi-square heterogeneity statistic.

^*If heterogeneity is not present (χ² < the degrees of freedom) then the Shore or random effects models are the same as the fixed effects model. The degrees of freedom is the number of studies minus one.

^†Includes all studies in Table 5 with exposure category not marked “Total cohort”.