# What is the Difference Between Specificity and Sensitivity

Specificity and sensitivity are two terms used to describe the accuracy of tests. They help to evaluate the performance of diagnostic tests, especially in medicine and statistics.

What is the difference between specificity and sensitivity? Sensitivity focuses on identifying those who truly have the condition being tested (true positives), while specificity focuses on identifying those who do not have the condition (true negatives).

### Key Areas Covered

1. What is Specificity
– Definition, Features
2. What is Sensitivity
– Definition, Features
3. Similarities Between Specificity and Sensitivity
– Outline of Common Features
4. Difference Between Specificity and Sensitivity
– Comparison of Key Differences
5. FAQ: Specificity and Sensitivity

### Key Terms

Specificity, Sensitivity, Test

## What is Specificity

Specificity refers to a test’s ability to correctly identify individuals who do not have the condition being tested. A test with high specificity would be like a system with minimal false alarms. Moreover, a false positive occurs when a test incorrectly identifies someone without the condition as positive.

Specificity is expressed as a mathematical formula. It’s the number of true negatives divided by the total number of individuals who actually do not have the condition (true negatives + false positives).

For example, consider the following situation.

True Negatives: Imagine 100 people who actually don’t have the foodborne illness. Ideally, the test would correctly identify all 100 of them as negative (true negatives).

False Positives: However, the test might mistakenly identify a few healthy individuals (out of those 100) as positive for the illness (false positives). Let’s say it incorrectly flags 5 people.

Specificity Calculation: Using the formula, Specificity = True Negatives / (True Negatives + False Positives), we get Specificity = 95 / (95 + 5) = 95%.

Specificity has different applications. It is used in medical testing, security systems, spam filtering, facial recognition technology, ecological monitoring, manufacturing, and quality controls.

## What is Sensitivity

Sensitivity is a measure of a test’s ability to correctly identify those who truly have the condition being investigated. The higher the sensitivity, the fewer the chances of missing a true case.

Sensitivity is expressed as a mathematical formula. When the number of true positives is divided by the total number of individuals who actually have the condition (true positives + false negatives), sensitivity is obtained.

A false negative occurs when a test incorrectly identifies someone with the condition as negative. Consider the following example. A sensitive HIV test is essential to identify individuals infected with the virus (true positives) and ensure they receive proper treatment and care. Missing cases due to low sensitivity can have serious health implications.

There are many applications of sensitivity. It is useful in medical testing, sensor design, and error detection in engineering, climate modeling and pollution monitoring in environmental science and survey design and economic modeling in social science.

## Similarities Between Specificity and Sensitivity

1. Specificity and sensitivity are important in accurate testing.
2. Both are expressed as percentages.

## Difference Between Specificity and Sensitivity

### Definition

• Specificity refers to a test’s ability to correctly identify individuals who do not have the condition being tested, while sensitivity refers to a test’s ability to correctly identify those who truly have the condition being investigated.

### Identifies

• Specificity identifies true negatives, while sensitivity identifies true positives.

### Calculation

• Specificity is calculated as True negatives / (True negatives + False positives). Meanwhile, sensitivity is calculated as True positives / (True positives + False negatives).

### Minimizes

• Specificity minimizes false positives, while sensitivity minimizes false negatives.

## Conclusion

Specificity ensures a test avoids false positives (identifying healthy individuals as having the condition), while sensitivity minimizes false negatives (missing true cases). This is the basic difference between specificity and sensitivity. Both are essential for reliable testing.

## FAQ: Specificity and Sensitivity

### 1. What if a test has high sensitivity but low specificity?

A test with high sensitivity but low specificity is good at catching the most true cases (positive) but also flags many healthy individuals (false positives) unnecessarily.

### 2. Is high or low sensitivity better?

High sensitivity minimizes missed cases but can lead to more false positives. Low sensitivity might reduce unnecessary worry but risks missing true positives. The ideal depends on the situation and the consequences of each error.

### 3. Does high sensitivity mean high accuracy?

High sensitivity catches most true positives, but it doesn’t guarantee high accuracy. A test can be very sensitive but also has low specificity, reducing overall accuracy.

### 4. How to calculate sensitivity?

Sensitivity is calculated by dividing the number of true positives (correctly identified cases with the condition) by the total number of individuals who actually have the condition (true positives + false negatives). This value is a percentage, with a higher value indicating a test’s ability to catch most true cases.

### 5. How to calculate specificity?

To calculate specificity, divide the number of true negatives (correctly identified individuals without the condition) by the total number of people who actually don’t have the condition (true negatives + false positives). Expressed as a percentage, a higher specificity indicates a test’s ability to minimize false positives.

##### Reference:

1. “Sensitivity and Specificity.” Wikipedia. Wikipedia Foundation.

##### Image Courtesy:

1. “Sensitivity and specificity 1.01” By FeanDoe – Modified version from Walber’s Precision and Recall  (CC BY-SA 4.0) via Commons Wikimedia

### About the Author: Hasini A

Hasini is a graduate of Applied Science with a strong background in forestry, environmental science, chemistry, and management science. She is an amateur photographer with a keen interest in exploring the wonders of nature and science.