Number needed to treat(NNT) is calculated based on the absolute risk reduction(ARR), it is inverse if ARR. Basically this is where we talk about how many patients we should treat to PREVENT one case of disease.(Question will talk about placebo treatment vs new treatment)
Number needed to harm(NNH) is calculated based in attributable risk(AR), it is inverse of AR. This is how we calculate how many people need to be exposed to a risk factor to DEVELOP one case of disease. (Question will talk about risk factor exposure)
Number needed to treat is calculated by dividing 1 by the absolute risk reduction --> 1/([C/C+D]-[A/A+B])
Number needed to harm is calculated by dividing 1 by the attributable risk --> 1/([A/A+B)-[C/C+D])
i would upload flashcards of this, but i dont have enough posts do so. if you have an android, you can check out the flash cards on an app called EpiStats. its an app im working on and trying to improve.
Memorizing formulas for ARR and NNT is probably not a good idea. In terms of working with data, it's better to get the concept so if you have to work with data that is presented in different forms, you can still work wit them
Here are the flashcards for number needed to treat and attributable risk. Check out the video lectures if you want a guide on how to make the calculation.
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