Summary of findings 2. Highest compared with lowest green tea exposure for preventing cancer: primary outcomes in nonexperimental studies.

Highest compared with lowest green tea exposure for preventing cancer in nonexperimental studies
Patient or population: adults (aged at least 18 years) Setting: outpatient Intervention: highest green tea exposure Comparison: lowest green tea exposure
Outcomes (number of studies)	Relative effect (95% CI)	Number of participants (number of cases)	Certainty of the evidence (GRADE)	Comments
Any cancer incidence (3 studies)	RR 0.83 (0.65 to 1.07)	52,479 (4962 cases)	⊕⊕⊝⊝ Low	Largea but imprecise effect. Similar but imprecise effect from the 2 cohort studies (RR 0.81, 95% CI 0.50 to 1.32)
Any cancer mortality (8 studies)	RR 0.99 (0.91 to 1.07)	504,366 (21,439 cases)	⊕⊕⊝⊝ Low	Not a large effect. All cohort studies
The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: confidence interval; RR: risk ratio
GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate; the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited; the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate; the true effect is likely to be substantially different from the estimate of effect.

^aUpgrading criteria for nonexperimental studies considered are: large effect estimates.