Positive Predictive Value Calculator


Instructions: This Positive Predictive Value Calculator computes the positive predictive value (PPV) of a test, showing all the steps. In order to do so, please fill up the 2x2 table below with the information about disease presence and absence, and screening test status:

Disease Present
Disease Absent
Test +
Test -

More about this Positive Predictive Value Calculator

The Positive Predictive Value a test (PPV) corresponds to the probability that a patient has the disease, given that the patient tests positive.

How do you compute the PPV a test?

Check out the following 2x2 crosstabulation about the results of the screening test and presence of the disease:

 
Disease Present
Disease Absent
Test +
\(TP\)
\(FP\)
Test -
\(FN\)
\(TN\)

• The value \(TP\) corresponds to the number of true positive cases, which is when the test shows positive for patients with the condition.

• The value \(FP\) corresponds to the number of false positive cases, which is when the test shows positive for patients who don't have the condition.

• The value \(FN\) corresponds to the number of false negative cases, which is when the test shows negative for patients with the condition.

• The value \(TN\) corresponds to the number of true negative cases, which is when the test shows negative for patients who don't have the condition.

Since \(TP + FP\) is the total number of those who test positive, the positive predictive value of the test is

\[\text{PPV} = \displaystyle \frac{TP}{TP + FP}\]

What are other related metrics to positive predictive value?

When working with the characteristics of a test, you probably are going to be interested in knowing about the specificity of the test, the sensitivity of the test, as well as the negative predictive value (NPV).

How to calculate sensitivity and specificity in excel

You need to follow the same calculation formula used above to compute the sensitivity and specificity of a test in Excel. First, you need to put the elements in the crosstabulation form specified above.




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