First, thank you so much. You motivated me with these videos. Making this pretty uncomplicated! With what I learned I detected couple minor mistakes that I’d like to share for better understanding of all. Hope it helps and thanks again! 13:08-13:13 I think you worded it incorrectly. You mention here that not excercising increases the risk of MI 25% BUT you used in the numerator (of this equation: ad/bc) the upper row which is “yes” to excercising. So I believe what you meant here was actually: “if you DO excercise you’ll have a 25% relative risk for MI as compared to not excercising” (this would mean that out of 100 persons who do not excercise and develop MI, only a fraction: 25%- 25 people that do excercise will get an MI). - 13:21-13:41: Here you are explaining Relative Risk Reduction. This equation isn’t a porportion, so just interchange word “over” for “minus”. Guess you meant-> 1 mimus 0,25: 0,75 (Since 0,25 was the relative risk). So for Relative Risk Reduction you have to REDUCe (subtract) the RELATIVE RISK-> 1- RR. - 14:21: Absolute Risk Reduction-> think of Absolute Vodka (distilled/ pure-> take out confounders and purify data). Absolute: purify. Refuction: subtract. So subtract the RRisks. ARR: (RR no excercise)- (RR excercise)-> 0,15/ 15%. - 15:30: NNTreat (beneficial effect) /NNHarm (most: harmfull). In this case excercise is beneficial so it’s NNT. NNT: 1/ ARR : 1/0,15 : 6,6-> rounds to 7. The NNT is 7. Read as: For every 7 people who excercise there is 1 MI prevented.
What a lad. Not doing the course you are explaining for but a similar Health based one in Pharmacy. Was able to completely link all the factors i struggled with. Thanks mate
ODDS RATIO = TP/FP / FN/TN or (Exposed with Disease/Exposed without Disease) / (Not Exposed with Disease / Not Exposed without Disease). Your ODDS RATIO Equation is Wrong. The ratio is A/B / C/D in your 2x2 table. You got lucky since you did the cross-product, but you conceptionally are wrong in your set up, understanding, and explanation. You can verify this in any biostats textbook.
There are two equations used for odds ratio. The exposure odds ratio (which is the one he used) and the disease odds ratio (which is what you are describing). They are equivalent. It does change how you describe the outcome. He is still correct as he was speaking of how the exposure changes your odds of getting the disease. In your example, you would describe people with the disease and their odds of having been exposed.
In disease odds ratio (what @cmetube describes) is equal to the (odds of disease given exposure) divided by (odds of disease given no exposure). Disease odds ratio = [(a / a+b )/(b / a+b )] / [(c / c+d )/(d / c+d)] = [a/b] / [c/d]. This is not conceptually the same as odds of exposure given disease.
Ly Med. if you are given the odds ratio for patients that were treated with Treatment A vs non-treated patients of OR= 0.40. From the group of people who do not have treatment A, 12 are not sick, 15 are sick. How we can calculate the risk of having the event for a patient who received Treatment A.? The risk ratio for the treated vs non-treated patients? and How many out of 20 patients are expected to have the event if they are treated with Treatment A?
might be but mostly not, two different concepts/"relative risks". NNH is a measure of harm or adverse effects, NNT is a measure of how many patients needed to be treated in order for one to benefit. (www.statisticshowto.datasciencecentral.com/number-needed-to-harm/)
