# Test Sensitivity Calculator

Instructions: This Sensitivity Calculator computes the sensitivity of a test, showing all the steps. To that end, please fill up the required table with the information about disease presence and absence, and screening test status:

Disease Present
Disease Absent
Test +
Test -

The sensitivity of a test corresponds to the probability that the test detects correctly people who have the disease.

### How do you compute the sensitivity of a test?

Let us consider the following 2x2 crosstabulation about test screening 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 $$TP + FN$$ is the total number of positive cases (people with the condition), the sensitivity of the test is computed as

$\text{Sensitivity} = \displaystyle \frac{TP}{TP + FN}$

### What are other related metrics to sensitivity?

When working with the characteristics of a test, you probably are going to be interested in knowing about the specificity of the test, the positive predictive value (PPV), 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.

Make sure to correctly identify the position of $$TP$$, $$TN$$, $$FP$$ and $$FP$$, because the result of the calculations WILL depend on the order to the inputs in the table, so make sure to be careful with that.

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