# Negative Predictive Value Calculator

Instructions: This Negative Predictive Value Calculator computes the negative predictive value (NPV) of a test, showing all the steps. Please provide the information required to fill out the 2x2 table below with the information about disease presence and absence, and screening test status:

Disease Present
Disease Absent
Test +
Test -

The Negative Predictive Value a test (NPV) corresponds to the probability that a patient does not have the disease, given that the patient tests negative.

### How do you compute the Negative Predictive Value of a test?

Consider 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 $$TN + FN$$ is the total number of those who test negative, the negative predictive value of the test is

$\text{NPV} = \displaystyle \frac{TN}{TN + FN}$

### What are other related metrics to negative predictive value (NPV)?

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 positive predictive value (PPV).

### How to calculate sensitivity and specificity, PPV and NPV using 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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