“This pill will reduce your sickness by 50%!!”


This is quite an exciting declaration. We hear these types of claims all the time, but what does it really mean?


Risk Reduction is a complicated topic to explain, but it is one of the most important concepts for patients to know.


Compare these two scenarios:


Scenario #1: Imagine that 40% of the population gets a sore throat infection every year. In other words, if we take 1000 average people, and track them over the next year, 400 out of those 1000 people will get sore throat.


Scenario #2: Imagine that 1% of the population will get a stomach ulcer every year. In other words, if we take 1000 average people, and track them over the next year, 10 out of of these 1000 people will get a stomach ulcer.



Now let’s say a new medication, called “Miracle Drug A”, comes out on the market. Miracle Drug A has been proven to “reduce the chances of someone getting a sore throat infection by 50%”. That means that if all of those 1000 people from Scenario #1 took the pill, instead of 400 of the getting a sore throat, this number is reduced by half (50%), so only 200 get a sore throat. In this example, Miracle Drug A saved 200 people from getting a sore throat.


Compare that to “Miracle Drug B” that has just come out on the market to reduce that chance of stomach ulcers. Miracle Drug B similarly “reduces the chances of someone getting a stomach ulcer by 50%”. This means that only 5, instead of 10, out of the 1000 people from Scenario #2 will get stomach ulcers.


Notice how both Miracle Drug A and Miracle Drug are both “50%” effective preventing the illness that they treat. Both sound like amazing medications. However, notice how Miracle Drug A saves 200 victims, whereas Miracle Drug B only saves 5 victims.



This illustrates the difference between the concepts of “RELATIVE Risk Reduction” versus “ABSOLUTE Risk Reduction”.


Both Miracle Drug A and Miracle Drug B have the same “Relative Risk Reduction” of 50%. That is, relative to how common the problem is, they both cut the rates of sickness in half (by 50%):






However, in terms of absolute numbers, the numbers look like this:






KEY CONCEPT: notice the huge difference when the numbers are reported as “Absolute Risk Reductions”, which is arguably the more important number to consider. Miracle drug A saved 20% of all the patients who take it, whereas Miracle Drug B only saved a mere 0.5%.


Notice how the benefit of the medication depends on how common the illness is to begin with. The sore throats in Scenario #1 were a much more common problem than the stomach ulcers in Scenario #2. Therefore, the benefit of Miracle Drug A is magnified in Scenario #1. In other words, the more common an illness is to begin with, the larger the number of people who will benefit from a medication to treat it; whereas if an illness is rare, less people overall will benefit from a treatment for it.


KEY CONCEPT: when considering how much benefit a person may get from a treatment, we need to consider how common the risk or illness is to begin with (i.e. one needs to consider the “baseline risk” of the problem).


These are key concepts that all doctors and patients need to be aware of. Most drug advertisements only report the relative benefits. They often neglect to show the true absolute benefits.


(Below is a short video that further illustrates these concepts)


– Dr. Adam Stewart

October 4, 2016