# Is positive predictive value affected by prevalence?

## Is positive predictive value affected by prevalence?

Prevalence thus impacts the positive predictive value (PPV) and negative predictive value (NPV) of tests. As the prevalence increases, the PPV also increases but the NPV decreases. Similarly, as the prevalence decreases the PPV decreases while the NPV increases.

Are sensitivity and specificity related to prevalence?

Whereas sensitivity and specificity are independent of prevalence. Prevalence is the number of cases in a defined population at a single point in time and is expressed as a decimal or a percentage.

Why does positive predictive value change with prevalence?

Positive and negative predictive values are influenced by the prevalence of disease in the population that is being tested. If we test in a high prevalence setting, it is more likely that persons who test positive truly have disease than if the test is performed in a population with low prevalence..

### What’s the difference between predictive value and sensitivity?

Sensitivity and Specificity vs. Predictive Values Sensitivity and specificity are intrinsic characteristics of a test and do not change regardless of the patient or population being tested. Correct interpretation (predictive value) of a positive or negative test will vary depending on the particular patient or population being tested.

What is the sensitivity and specificity of a PPV test?

For any given test, as disease prevalence in the population being tested increases, the PPV of that test will also increase. Positive Predictive Values (PPV) Test with 90% Sensitivity and 90% Specificity in a Population with Disease Prevalence of 1%  PPV = .08 (8%)

How is sensitivity and specificity of disease calculated?

If these results are from a population-based study, prevalence can be calculated as follows: Prevalence of Disease= T disease Total × 100 The population used for the study influences the prevalence calculation. Sensitivity is the probability that a test will indicate ‘disease’ among those with the disease:

## How is sensitivity related to ovarian cancer specificity?

1540 1540 + 310 .83 = 83% sensitivity 13 CA-125 Protein as a Marker for Ovarian Cancer Specificity A specific test is usually negative in disease free patients (few false positives ). When many disease free patients have a positive test (false positives), the specificity decreases.