Evidence-Based Practice Guidelines: Stats Calculators

This multi-functional tool allows you to calculate data for several different types of evidence--diagnostic tests, prospective studies, case control studies, and randomized controlled trials (RCTs).

Diagnostic Test - calculates the Sensitivity, Specificity, PPV, NPV, LR+, and LR-
Prospective Study - calculates the Relative Risk (RR), Absolute Relative Risk (ARR), and Number Needed to Treat (NNT)
Case-control Study - calculates the Odds Ratio (OR)
Randomized Control Trial (RCT) - calculates the Relative Risk Reduction (RRR), ARR, and NNT

The LR is used to assess how good a diagnostic test is and to help in selecting an appropriate diagnostic test(s) or sequence of tests. They have advantages over sensitivity and specificity because they are less likely to change with the prevalence of the disorder, they can be calculated for several levels of the symptom/sign or test, they can be used to combine the results of multiple diagnostic test and the can be used to calculate post-test probability for a target disorder.

In statistics, the odds ratio (usually abbreviated "OR") is one of three main ways to quantify how strongly the presence or absence of property A is associated with the presence or absence of property B in a given population.

To convert odds ratios to NNTs, enter a number that is > 1 or < 1 in the odds ratio textbox and a number that is not equal to 0 or 1 for the Patient's Expected Event Rate (PEER). After entering the numbers, click "Calculate" to convert the odds ratio to NNT.

In statistics and epidemiology, relative risk or risk ratio (RR) is the ratio of the probability of an event occurring (for example, developing a disease, being injured) in an exposed group to the probability of the event occurring in a comparison, non-exposed group.