Short teaching lessons
Specificity explained with a veterinary exam example
Prepared 23 October 2026 · VetQ
Specificity asks: among animals that truly do not have the condition, what proportion test negative? The denominator contains nondiseased animals. It is different from the proportion of negative test results that are correct.
For veterinary exam study. These short examples do not prescribe treatment for an individual patient.
Count true negatives and false positives
In an invented evaluation, 200 animals do not have the condition according to the reference classification. The test returns 190 negatives and 10 positives. Specificity is 190 ÷ (190 + 10) = 95%. Those ten positives are false positives.
Compare specificity with sensitivity
Sensitivity uses the diseased group; specificity uses the nondiseased group. Draw a two-by-two table and label disease status before filling in results. This prevents switching denominators when an exam question gives several totals.
Read what the question actually asks
“How often is disease absent when the test is negative?” asks for negative predictive value, not specificity. Word order matters. Write the population named after “among” or “given” before choosing a formula. Performance estimates also depend on the evaluation setting and reference standard.
Use the same table for different questions
In a fictional table with 45 true positives, 5 false negatives, 15 false positives and 135 true negatives, the nondiseased group contains 150 animals. Specificity is 135 ÷ 150 = 90%. If asked for the proportion of negative results that are correct, the denominator changes to 135 + 5, producing approximately 96.4%. Both calculations are valid, but they answer different questions. Write a short sentence describing each denominator before calculating. A common error is performing accurate arithmetic on the wrong population. Practise translating the question into a group first, then choose the numerator and denominator deliberately rather than relying on the words positive or negative alone.
Check your understanding
Of 300 nondiseased animals in a fictional study, 24 test positive. What is specificity?
Read the answer and reasoning
There are 276 true negatives and 24 false positives. Specificity = 276 ÷ 300 = 92%. Dividing by all positive tests would answer a different question.
Keep reading
- Sensitivity explained with a veterinary exam example
- Why can a positive veterinary test be wrong? Predictive value explained
- Epidemiology and Preventive Medicine exam questions: topics, study tips and free sample questions
Sources and further reading
Source pages checked 23 October 2026. Examples and study routines on this page are original teaching material, not official examination items.