Medical Abbreviations: Part III of a III Part Article

Evidence-Based Medicine and Statistical Terms

(6/8/07)-(These terms will prove helpful when you read some of the original research studies referred to in the research literature.)

Sensitivity (Sn): percentage of patients with disease who have a positive test for the disease in question

Specificity (Sp): percentage of patients without disease who have a negative test for the disease in question.

Predictive value-positive and negative (PV+/PV-): Percentage of patients with a positive or negative test for a disease who do or do not have the disease in question.

Pretest probability: Probability of disease before a test is performed.

Post-test probability: Probability of disease after a test is performed.

Likelihood ratio (LR): LR>1 indicates an increased likelihood of disease, LR<1 indicates a decreased likelihood of disease. The most helpful tests generally have a ratio of less than 0.2 or greater than 5.

Relative risk reduction (RRR): The percentage difference in risk or outcomes between treatment and control groups. Example: if mortality is 30% in controls and 20% with treatment, RRR is (30-20)/30=33%.

Absolute risk reduction (ARR): The arithmetic difference in risk or outcome between treatment and control groups. Example: if mortality is 30% in controls and 20% in treatment, ARR is 30-2-=10%.

Number needed to treat (NNT): The number of patients who need to receive an intervention instead of the alternative in order for one additional patient to benefit. The NNT is calculated as: 1/ARR. Example. If the ARR is 4%, the NNT=1/4%=1/0.04=25.

95 percent confidence interval (95%CL): An estimate of precision. If a study is repeated 100 times, the results will fall within this range 95 times.

Systematic review: A type of review that uses explicit methods to comprehensively analyze and qualitatively synthesize information from multiple studies.

Meta-analysis: A type of systematic review that uses rigorous statistical methods to quantitatively synthesize the results of multiple similar studies.

(8/05/06) Back in 2001, we wrote our first article on medical abbreviations. We never anticipated what a continuing success it would be in terms of the number individuals who "hit" these articles each month for the last 5 years. We are now happy to see that the US Food and Drug Administration and the Institute for Safe Medication Practices have launched a campaign to reduce medication mistakes caused by the use of unclear medical abbreviations. This site ( does not claim we prodded them into this step, but we wonder why it took so long to institute such a campaign in light of the more than 7000 deaths that occur in the United States each year due to medication errors.

The primary goal of the campaign is to eliminate confusing abbreviations, symbols and dose designations. The example usually cited is the abbreviations IV and IU, which when written can be interchanged by someone reading the handwritten letters. It could even be mistaken for the number 10. For a full list of error-prone terms and abbreviations, we recommend you go to the Institute for Safe Medicine site at

We accessed the site on August 3, 2006 and copied the following material for our readers. This is the multilevel approach adopted by the FDA and the Institute for Safe Medicine. Health Care professionals need to address this issue in their everyday work.


Our hope is that this information proves helpful to our many readers and that a road map has been developed to eliminate the needless deaths caused by medication mistakes.

Please see: -
Medical Abbreviations-Part I
Medical Abbreviations found in Medical Charts-Part II


Harold Rubin, MS, ABD, CRC, Guest Lecturer
updated June 8, 2007

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