**Test Taking Tips**

Memorize the following table for easy calculation of sensitivity, specificity, and positive and negative predictive values.

Know the differences between different types of statistical tests.

Not a lot changes in statistics, so similar questions are phrased differently annually.

The proportion of truly diseased persons in a screened population who are identified as being diseased by the test. It is a measure of the probability of correctly diagnosing a condition.

True positive / (true positive + false negative)

The proportion of truly nondiseased persons who are so identified by the screening test

True negative / (false positive + true negative)

1 – specificity

1 – sensitivity

The probability that a person with a positive test result has the disease

True positive / (true positive + false positive)

The probability that a patient with a negative test result really is free of the disease

True negative / (false negative + true negative)

The total number of cases of a given disease in a specified population at a designated time

The number of new cases of a given disease during a given period in a specified population

The absolute arithmetic difference in outcome rates between control and experimental patients in a trial

The proportional reduction in outcome rates between control and experimental patients in a trial

Confidence interval

### A method of studying a drug or procedure in which both the subjects and investigators are kept unaware of who is actually getting which specific treatment is called what?

Double-blind method

Number needed to treat