Table 3. Meta-regression analyses on trials with low risk of bias.

Covariates	Trials (N)	Univariate				Multivaraite
		RR	95% CI		P	RR	95% CI		P
Dose of beta-carotene	26	1.005	0.999	1.01	0.12	1.005	0.998	1.012	0.15
Type of prevention*		1.032	0.933	1.142	0.54	1.021	0.923	1.130	0.68
Administered singly or combined		1.003	0.907	1.109	0.95	0.990	0.900	1.089	0.83
Dose of vitamin A	12	1.00002	1.000004	1.00004	0.017	1.00002	1.000001	1.00004	0.039
Type of prevention*		1.111	0.880	1.403	0.38	1.156	0.910	1.470	0.24
Administered singly or combined		1.105	0.733	1.665	0.63	1.161	0.748	1.803	0.51
Dose of vitamin E	46	1.00002	0.999	1.0001	0.68	1.00002	0.999	1.0001	0.70
Type of prevention*		0.989	0.924	1.059	0.76	0.982	0.905	1.067	0.67
Administered singly or combined		1.028	0.960	1.100	0.44	1.039	0.964	1.120	0.31

Abbreviations: RR-relative risk; CI-confidence interval.

^*Either primary prevention or secondary prevention.