Epidemiological Studies

NPV is defined as the probability of being free of a disease if the test result is negative.

NPV will vary with the pretest probability of a disease (ie., disease prevalence).

A patient with a high probability of having a disease will have a low NPV, and a patient with a low probability of having a disease will have a high NPV.

The prevalence of a disease is directly related to the pre-test probability of having the disease, and also affects the NPV.

NPV: If you have a negative test, what is the likelihood you really DON’T have the disease?

PPV: If you have a positive test, what is the likelihood you really DO have the disease?

Sensitivity: If you DO have the disease, what is the likelihood you will have a positive test?

Specificity: If you DON’T have the disease, what is the likelihood you will have a negative test?

Key Terms:

Bias = deviation from the truth

Reliability = consistency or precision

Validity =  accuracy or hitting the target

Observational Studies

Case report