Interpretation of Risk Ratio in Cohort Study
The correct answer is A: Green tea drinkers have a lower risk of DM. A risk ratio of 0.85 means that green tea drinkers have 85% of the risk compared to black tea drinkers, which translates to a 15% reduction in diabetes risk.
Understanding Risk Ratio Interpretation
A risk ratio (RR) of 0.85 indicates that the exposed group (green tea drinkers) has a 15% lower risk of developing diabetes compared to the unexposed group (black tea drinkers). 1
Why Each Answer Choice is Correct or Incorrect:
Option A is CORRECT: Green tea drinkers have 0.85 times the risk of black tea drinkers, meaning they have a lower risk of diabetes. This is consistent with meta-analyses showing that both green and black tea consumption are associated with reduced diabetes risk, with green tea showing particularly strong inverse associations. 1
Option B is INCORRECT: While the RR suggests green tea has a protective effect relative to black tea, this does NOT mean black tea increases diabetes risk. Black tea itself is associated with reduced diabetes risk in meta-analyses (4.6% reduced risk per 2 cups/day increase). 1 The comparison simply shows green tea may be more protective than black tea, not that black tea is harmful.
Option C is INCORRECT: An RR of 0.85 clearly shows an association between the exposure (green tea) and outcome (diabetes), with green tea associated with lower risk. 2, 3
Option D is INCORRECT: Without confidence intervals or p-values provided, we cannot determine if results occurred by chance. However, the question asks for interpretation of the point estimate (RR = 0.85), which indicates a 15% risk reduction regardless of statistical significance. 2, 3
Clinical Context
Both green and black tea consumption are associated with reduced diabetes risk in large meta-analyses, with dose-dependent effects. 1 Consumption of ≥4 cups/day of tea is associated with a 17% reduced risk of type 2 diabetes. 2 Green tea consumption specifically shows a 5% lower risk of cardiovascular mortality and 4% lower risk of all-cause mortality per cup per day. 4
Important Caveats:
- The RR of 0.85 represents a relative comparison between two groups, not an absolute measure of risk. 1
- This interpretation assumes the study controlled for confounding variables and that the association is causal, which observational cohort studies cannot definitively prove. 2, 3
- The magnitude of benefit appears dose-dependent, with higher consumption (≥3-4 cups/day) showing more pronounced risk reduction. 2, 3, 5