Table 3. Stratified pooled relative risks and 95% confidence intervals for highest versus lowest category of circulating beta-carotene and all-cause mortality.

Subgroups		n	Death	Participants	RR	95%CI	I2 (%)	Pa	Pb
All studies		7	6137	25468	0.69	0.59, 0.80	37.10	0.145
Duration of follow-up									0.496
	< 10 years	4	565	6121	0.62	0.47, 0.82	0	0.494
	> = 10 years	3	5572	19347	0.71	0.57, 0.88	67.20	0.047
Sample size									0.246
	<2,000	3	1038	2383	0.81	0.67, 0.97	0	0.600
	> = 2,000	4	5099	23085	0.63	0.51, 0.78	46.60	0.132
Population age at baseline									0.246
	<50	4	5099	23085	0.63	0.51, 0.78	46.60	0.132
	> = 50	3	1038	2383	0.81	0.67, 0.97	0	0.600
Median level									0.076
	<350 nmol/L	2	661	2439	0.54	0.42, 0.70	0	0.688
	> = 350 nmol/L	5	5476	23029	0.75	0.66, 0.86	9.30	0.354
Blood sample									0.197
	Serum	5	5130	23239	0.63	0.52, 0.77	34.00	0.194
	Plasma	2	1007	2229	0.82	0.68, 0.99	0	0.741
Major confounders adjusted
History of disease									0.560
	Yes	3	4546	17337	0.74	0.63, 0.88	0	0.703
	No	4	1591	8131	0.64	0.49, 0.84	63.80	0.040
Smoking and drinking									0.962
	Yes	4	4759	21975	0.71	0.61, 0.83	1.40	0.385
	No	3	1378	3493	0.66	0.46, 0.96	69.20	0.039
BMI									0.560
	Yes	3	4546	17337	0.74	0.63, 0.88	0	0.703
	No	4	1591	8131	0.64	0.49, 0.84	63.80	0.040
Physical activity									0.572
	Yes	4	4692	19781	0.74	0.63, 0.86	0	0.839
	No	3	1445	5687	0.62	0.44, 0.89	75.90	0.016
Serum cholesterol level									0.471
	Yes	3	4661	19627	0.74	0.63, 0.87	0	0.918
	No	4	1476	5841	0.61	0.44, 0.85	65.90	0.032
Vitamin supplementation use									0.454
	Yes	2	4515	17183	0.75	0.64, 0.89	0	0.960
	No	5	1622	8285	0.63	0.49, 0.82	54.60	0.066

Abbreviation: RR, relative risk; CI, confidence interval; I ², measure of heterogeneity; P_a, P value for heterogeneity within each group; P_b, P value for heterogeneity between subgroups in meta-regression.