# http://www.fpnotebook.com/

## Positive Predictive Value

Aka: Positive Predictive Value
2. Definition
1. Percent of patients with positive test having disease
2. Assesses reliability of positive test
3. Indications
1. Puts Test Specificity in context of disease Prevalence
2. Lower disease Prevalence results in lower PPV
1. Test Specificity effect is magnified
2. False positives increase substantially
3. Results in less reliable positive test
4. Calculation
1. PPV = (True positive) / (True + False positives)
5. Example 1: High Prevalence Disease
1. Major DepressionPrevalence is 10 per 100
2. New Screening Test efficacy
1. Test Sensitivity: 100%
2. Test Specificity: 99% (1 false positive in 100)
3. Screen 1000 patients
1. True positives: 100 per 1000 (10% Prevalence)
2. False positives: 10 per 1000 (99% Test Specificity)
3. PPV: 100 true positives / 110 total positives = 91%
6. Example 2: Low Prevalence Disease
1. SclerodermaPrevalence is 1 per 1000
2. New Screening Test efficacy
1. Test Sensitivity: 100%
2. Test Specificity: 99% (1 false positive in 100)
3. Screen 1000 patients
1. True positives: 1 per 1000 (0.1% Prevalence)
2. False positives: 10 per 1000 (99% Test Specificity)
3. PPV: 1 true positive / 11 total positives = 9%
1. Contrast with PPV 91% for high Prevalence disease

### Positive Predictive Value of Diagnostic Test (C1514243)

Definition (NCI) The likelihood that an individual with a positive test result truly has the particular gene and/or disease in question.
Definition (NCI) The probability that an individual is affected with the condition when a positive test result is observed. Predictive values should only be calculated from cohort studies or studies that legitimately reflect the number of people in the population who have the condition of interest at that time since predictive values are inherently dependent upon the prevalence. PPVDT can be determined by calculating: number of true positive results divided by the sum of true positive results plus number of false positive results.
Concepts Quantitative Concept (T081)
English positive predictive value, PPV, Positive Predictive Value of Diagnostic Test
Sources
Derived from the NIH UMLS (Unified Medical Language System)