Editing Evidence-based medicine (section)

=== Statistical measures ===
Evidence-based medicine attempts to express clinical benefits of tests and treatments using mathematical methods. Tools used by practitioners of evidence-based medicine include:
* Likelihood ratio {{Main|Likelihood ratios in diagnostic testing}} The [[pre-test odds]] of a particular diagnosis, multiplied by the likelihood ratio, determines the [[pre- and post-test probability|post-test odds]]. (Odds can be calculated from, and then converted to, the [more familiar] probability.) This reflects [[Bayes' theorem]]. The differences in likelihood ratio between clinical tests can be used to prioritize clinical tests according to their usefulness in a given clinical situation.
* AUC-ROC The area under the [[receiver operating characteristic]] curve (AUC-ROC) reflects the relationship between [[sensitivity and specificity]] for a given test. High-quality tests will have an AUC-ROC approaching 1, and high-quality publications about clinical tests will provide information about the AUC-ROC. Cutoff values for positive and negative tests can influence specificity and sensitivity, but they do not affect AUC-ROC.
* [[Number needed to treat]] (NNT)/[[Number needed to harm]] (NNH). NNT and NNH are ways of expressing the effectiveness and safety, respectively, of interventions in a way that is clinically meaningful. NNT is the number of people who need to be treated in order to achieve the desired outcome (e.g. survival from cancer) in one patient. For example, if a treatment increases the chance of survival by 5%, then 20 people need to be treated in order for 1 additional patient to survive because of the treatment. The concept can also be applied to diagnostic tests. For example, if 1,339 women age 50–59 need to be invited for breast cancer screening over a ten-year period in order to prevent one woman from dying of breast cancer,<ref name="BandolierStatins2004">"Patient Compliance with statins" ''[[Bandolier (journal)|Bandolier]]'' [http://www.medicine.ox.ac.uk/bandolier/booth/cardiac/patcomp.html Review] 2004 {{Webarchive|url=https://archive.today/20150512021122/http://www.medicine.ox.ac.uk/bandolier/booth/cardiac/patcomp.html |date=12 May 2015 }}</ref> then the NNT for being invited to breast cancer screening is 1339.