A meta-analysis of multiple trials on the effect of cocoa consumption on systolic blood pressure (SBP) yielded the following findings: All of the trials looked at the change in SBP after two weeks. Which of the following is the most appropriate conclusion based on the data?

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Quizplus · Accepted Answer

Eductional Objective: A meta-analysis combines the findings of numerous trials (preferably, high-quality randomized controlled trials) to improve statistical power and offer an overall estimate of the influence of an exposure (for example, chocolate consumption) on an outcome (eg, systolic blood pressure [SBP]). Individual trial findings are evaluated and weighted to get a pooled effect estimate. In this case, the meta-analysis revealed a 2.2 mm Hg drop in mean SBP in the cocoa consumption group as compared to the control group. Because the CI does not contain the null value, the 95 percent confidence interval (CI) was 2.7 to 1.3 mm Hg, showing a statistically significant difference (explained below). Based on sample findings, CIs provide a range of feasible values for an unknown parameter (e.g., difference between two mean SBPs). If the CI does not cross the null value, the result is statistically significant; if it does, the result is not statistically significant. Every CI has a null value, however it is not the same for every CI. The null value for an odds ratio or a relative risk (RR) is 1 since these statistics are ratios (RR = 1 shows no difference in risk between the groups). If, on the other hand, the parameter of interest is a difference (eg, difference in mean SBP between cocoa intake and control groups),then the null value is 0 because that represents no difference between the groups.
In this case, the 95% CI of [-2.7, -1.3] does not include the null value of 0 and therefore the result is statistically significant. In summary, cocoa intake was associated with a statistically significant decrease in SBP.

A Meta-Analysis of Multiple Trials on the Effect of Cocoa