You are currently tasked for the upcoming journal club at your hospital to review a recent study on a newer agent in the management of chronic heart failure. There were no significant differences in baseline characteristics between the two groups.The primary outcome studied was a composite outcome of death from cardiovascular causes or hospitalization for heart failure, studied over a 36 month period. At the time of study cessation, the primary outcome had occurred in 22% of patients in the new drug therapy arm and 27% of patients in the standard of therapy arm. The corresponding hazard ratio for the new drug group was 0.80; 95% Confidence Interval, 0.71 to 0.89; p< 0.001). How would this study's primary outcome be best interpreted?

A. The newer agent is statistically inferior than the current standard. The number needed to harm is 20.

B. The newer agent is statistically significantly better than the standard therapy for the primary outcome; however a number needed to treat cannot be calculated.

C. The newer agent is statistically significantly better than the standard therapy for the primary outcome; the number needed to treat is 20.

D. The newer agent is similar to the current standard with regards to the primary outcome.

Answer with Rationale

The correct answer is C. Interpreting statistics within a study is a very important part of literature evaluation. While we are not expected to be statisticians, knowing how to perform basic calculations with regards to literature evaluation is essential. The number needed to treat or NNT is a way to measure the impact of a study intervention on a single person; meaning how many subjects do you have to treat to get the outcome studied. For the study shown, the hazard ratio of the newer agent is lower than the standard with a statistically significant p-value and a confidence interval that does not include 1; therefore the result is significant in favor of the newer agent making answers A and D incorrect. Answer B is incorrect as you can indeed calculate a NNT because the result is statistically significant. You take the absolute difference (in this case 5%), and divide 1/0.05 which gives you 20 which is a low NNT for an important outcome such as cardiovascular morbidity and mortality. While the safety outcomes were not presented in this case, you would have to balance those results versus these efficacy results which are promising to fully evaulate the study.