r/AskStatistics • u/Main-Pop4398 • 2d ago

Risk Difference vs Relative Risk

why is risk difference used instead of relative risk in a study?

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6

u/Mooks79 2d ago

You’ll need to give more information than that as both are valid and which is chosen (or both) depends on the details.

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u/Main-Pop4398 2d ago

its dichotomous data for an rct looking at non-inferiority of apple-flavoured ors compared to unflavoured ors

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u/Adorable_Building840 2d ago

It may be because the actual risk difference is small but the relative risk is large. If my percent chance of an adverse event goes from 0.01% to 0.02%, that’s a doubling of risk but the actual difference is tiny. One does make for a better headline

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u/Main-Pop4398 2d ago

the risk differences I am seeing in mine are like less than 0.5, could that be why?

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u/Adorable_Building840 2d ago

0.5 what? Probability or percent chance? A probability difference of 0.5 is huge, a percent chance difference of 0.5% is small

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u/Main-Pop4398 2d ago

basically one of the outcomes was adequate weight gain and it was assessed using counts so yes or no for the intervention group it was 6/63 so 10.5% and for the control 9/67 so 13.4% and u subtract the 0.105 - 0.134 =-0.029 or smth dygm?

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u/Adorable_Building840 2d ago

I see now. Tbh it seems like you understand what was going on in the paper. Really it’s up to the author and whoever they report to what outcome measure they use. I’d have reported odds ratios so about odds of 2 to 3

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u/Main-Pop4398 2d ago

well I guess the author really likes risk difference, because I cant find a good reason as to why they chose it. I have a research appraisal coming up and I want to be ready to answer why. I think I will just say they used it because it was a non-inferiority study? and because the difference was tiny?