 
* 25 equations in biostats 
 #850236 




Not all of these equations are important for the usmle, but its helpful to learn a few. and if you know a little biostats and can visualize a two by two sample table, then you can probably figure out most of them.
Sensitivity = A / (A+C)
False Negative Rate = C / (A+C)
Specificity = D / (B+D)
False Positive Rate = B / (B+D)
Positive Predictive Value = A / (A+B)
False Discovery Rate = B / (B+D)
Negative Predictive Value = D / (C+D)
False Omission Rate = C / (C+D)
Positive Likelihood Ratio = [A / (A+C)] / [B / (B+D)]
Negative Likelihood Ratio = [C / (A+C)] / [D / (B+D)]
Informedness = [A / (A+C)] + [D / (B+D)]  1
Markedness = [A / (A+B)] + [D / (C+D)]  1
Accuracy = (A+D) / (A+B+C+D)
Precision = A / (A+B)
Relative Risk = [A / (A+B)] / [C / (C+D)]
Relative Risk Reduction = 1  [A / (A+B)] / [C / (C+D)]
Absolute Risk Reduction = [C / (C+D)]  [A / (A+B)]
Number Needed To Treat = 1 / [C / (C+D)]  [A / (A+B)]
Attributable Risk = [A / (A+B)]  [C / (C+D)]
Number Needed To Harm = 1 / [A / (A+B)]  [C / (C+D)]
Odds of Exposure (Cases) = A / C
Odds of Exposure (Controls) = B / D
Odds Ratio = (A / C) / (B / D)
Prevalence = [(A+C) / (A+B+C+D)]
Incidence = [(A+C) / (A+B+C+D)] / Time Period
i tried to organize these equations in a way thats easy to follow. 

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