The difference between relative versus absolute risk reported in studies

New reports often reports the relative risk or benefits between two groups (say a control group versus treatment group).   This number is usually deceptively higher than the absolute risk or benefit.

What is the difference between relative risk versus absolute risks? has a good explanation.   Suppose that 2 person out of 100 in a control non-treated group ended up with cancer.  And supposed that only 1 person out of 100 in a treatment group ended up with cancer.  Hence the relative risk would be a 50% decrease in breast cancer in the treatment group.  This is arrived at by taking the change and dividing by the initial value:  (2 – 1) / 2 = 0.5 = 50%    This is the number often reported.   Sounds pretty good right?

But consider the absolute risk.   Since the risk of cancer is 2% in the non-treated group, and the risk of cancer in the treated group is 1%, the treatment only reduced the risk from 2% to 1%.  This is only a 1% reduction in absolute risk.  Now it doesn’t sound that great.   This number is arrived at by taking the change in percentage divided by the overall percentage: (2-1)/100 = 0.01 = 1%.

Presentation by Sally Fallon-Morell also gives examples of how distorting the reports of relative risk are.  Video presentation on YouTube.

Tom Naughton is a comedian that did a bit at the Ancestral Health Symposium called “Science for Smart People” in which among the other topics talked about relative risk versus absolute risk…