A 50-year-old gentleman is admitted to the Cardiology ward having suffered a myocardial infarction. He is started on numerous medications for secondary prevention and has done some reading up whilst recuperating on the ward. In particular, he some questions regarding rosuvastatin as he has heard that it is a highly effective drug.


He would like to discuss a study he read in a journal. The data is as follows:


|Outcome|Rosuvastatin group<br />(N=2500)|Placebo group<br />(N=2500)|Relative Risk <br />(95% CI)|
|---------------------------------------|--------------------------------|---------------------------|----------------------------|
|Cardiovascular events (including death)|350 (14%)|560 (22.4%)|0.63 (0.59 - 0.72)|
|Death from non- cardiovascular causes|110 (4.4%)|125 (5.0%)|0.88 (0.80 - 1.05)|
|Death from any cause|270 (10.8%)|325 (13.0%)|0.83 (0.75 - 1.10)|


 _N (Total number of people in the group), CI (Confidence Interval)_


Which of the following is true based on the data above?

Options:
explanation: The NNT is calculated by taking the reciprocal of the absolute risk reduction. In this case, it would be 1/(22.4% - 14%) = 1/(8.4%) = 12
name: The number needed to treat (NNT) to prevent one cardiovascular event on rosuvastatin is 8
label: e
answer: no
explanation: ARR is calculated by taking the absolute risk (AR) of the placebo group and subtracting from it the AR of the therapeutic group. In this case, ARR = 5.0% - 4.4% = 0.6%
name: The absolute risk reduction (ARR) of death from non-cardiovascular causes is 0.88
label: c
answer: no
explanation: The relative risk reduction is calculated by taking the difference between the absolute risk in the control and therapeutic groups and dividing it by the absolute risk of the control group. In this case, it would be (22.4 - 14) / 22.4 = 37.5%
name: The relative risk reduction of cardiovascular events for patients on rosuvastatin is 37.5%
label: a
answer: yes
explanation: Confidence interval (CI) is a measure of how confident the study's authors are that the true population value lies within a particular range, and it is usually 95%. If the confidence interval does not include the null hypothesis value (for relative risk, this value is 1), we can say a statistically significant difference exists. In this case, as the CI is from 0.75 - 1.10 and includes 1, there is no significant reduction in death from all causes
name: There is a statistically significant reduction in death from all causes in patients on rosuvastatin
label: b
answer: no
explanation: Confidence interval (CI) is a measure of how confident the study's authors are that the true population value lies within a particular range, and it is usually 95%. If the confidence interval does not include the null hypothesis value (for relative risk, this value is 1), we can say a statistically significant difference exists. In this case, as the CI is from 0.75 - 1.10 and includes 1, there is no significant reduction in death from all causes
name: There is no statistically significant reduction in cardiovascular events, (including death) in patients on rosuvastatin
label: d
answer: no

Correct answer: a

The relative risk reduction of cardiovascular events for patients on rosuvastatin is 37.5%

Learning point: Relative Risk Reduction (RRR) is a measure used to compare the risk of an event between two groups. It is calculated by taking the difference between the absolute risk in the control and therapeutic groups and dividing it by the absolute risk of the control group.