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Evidence Based Medicine

Evidence Based Medicine


Likelihood Ratio is the likelihood that a given test result would be expected in a patient with the target disorder compared to the likelihood that the same result would be expected in a patient without that disorder.

Meta-analysis is an overview which uses quantitative methods to summarise the results.

Negative Predictive Value (-PV) is the proportion of people with a negative test who are free of disease.

Number Needed to Treat (NNT) is the number of patients who need to be treated to prevent one bad outcome in a period of time. It is the inverse of the ARR:

NNT = 1/ARR.

Odds are a ratio of events to non-events. If the event rate for a disease is 0.1 (10 per cent), its nonevent rate is 0.9 and therefore its odds are 1:9, or 0.111. Note that this is not the same expression as the inverse of event rate.

Odds Ratio describes the odds of an experimental patient suffering an adverse event relative to a control patient.

Overview is a systematic review and summary of the medical literature.

Positive Predictive Value (+PV) is the proportion of people with a positive test who have disease.

Randomised Controlled Clinical Trial a group of patients is randomised into an experimental group and a control group. These groups are followed up for the variables / outcomes of interest.

Relative Risk Reduction (RRR) is the percent reduction in events in the treated group event rate (EER) compared to the control group event rate (CER):

RRR = (CER - EER) / CER * 100

Risk Ratio is the ratio of risk in the treated group (EER) to the risk in the control group (CER): RR = EER/CER. RR is used in randomised trials and cohort studies.

Sensitivity is the proportion of people with disease who have a positive test.

Specificity is the proportion of people free of a disease who have a negative test.

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