hazard ratio and relative risk difference

In our review of a news release from the National Institutes of Health, we called them out for only using relative risk reductions from a study about intensive blood pressure management. This inclusion of absolute numbers helps readers get a much better sense of the overall differences we’re talking about here. At the same time, serious bleeding events increased from 0.07 percent among non-aspirin takers to 0.10 percent among those taking aspirin, or a 40 percent relative increase in risk. That corresponds to a 20 percent relative reduction in risk.

In a meta-analysis of the six major randomized trials of aspirin for primary prevention, among more than 95,000 participants, serious cardiovascular events occurred in 0.51 percent of participants taking aspirin and 0.57 percent of those not taking aspirin. In our review of a STAT story on new aspirin guidelines, we praised them for using both absolute and relative numbers. Only by knowing what the coupon’s true value is–the absolute data–does the 50% have any meaning. But you don’t know if the coupon applies to a diamond necklace or to a pack of chewing gum. They say that knowing only the relative data is like having a 50% off coupon for selected items at a department store. Steve Woloshin and Lisa Schwartz of the Dartmouth Institute for Health Policy & Clinical PracticeĮxplain absolute-relative risk in a creative way. Given the data above, the relative difference is:Įxpressed as a relative difference, the new drug reduces the risk for heart attack by half. The relative difference is the ratio of the two risks. If the 5-year risk for heart attack is 2 in 100 (2%) in a group of patients treated conventionally and 1 in 100 (1%) in patients treated with the new drug, the absolute difference is derived by simply subtracting the two risks: 2% – 1% = 1%.Įxpressed as an absolute difference, the new drug reduces the 5-year risk for heart attack by 1 percentage point. That’s why absolute numbers matter: They provide readers with enough information to determine the true size of the benefit. The risk halved, but in a far less impressive fashion. Yet it sounds significantly less great when you realize we’re actually talking about a 2% risk dropping to a 1% risk. “New drug cuts heart attack risk in half.” Why you should always use absolute risk numbers:

Hazard ratio and relative risk difference