Effect of prevalence on sensitivity, specificity, positive and negative predictive value

Q: What is disease prevalence? show answer

A: The percentage of a population with the disease.

Q: How does prevalence affect sensitivity and specificity? show answer

A: Sensitivity and specificity are unaffected by disease prevalence. Keep in mind that this assertion is not universally accepted.

Q: How will increasing disease prevalence affect negative predictive value? show answer

A: As prevalence increases, the negative predictive value decreases. For example, if disease prevalence reaches 100%, any negative test result will be a false negative. That means that the negative predictive value is 0%.

Q: How will decreasing disease prevalence affect negative predictive value? show answer

A: As prevalence decreases, the negative predictive value increases. For example, if disease prevalence reaches 0%, any negative test result will be a true negative. That means that the negative predictive value is 100%.

Q: How will increasing disease prevalence affect positive predictive value? show answer

A: As prevalence increases, the positive predictive value increases. For example, if disease prevalence reaches 100%, any positive test result will be a true positive. That means that the positive predictive value is 100%.

Q: How will decreasing disease prevalence affect positive predictive value? show answer

A: As prevalence decreases, the positive predictive value decreases. For example, if disease prevalence reaches 0%, any positive test result will be a false positive. That means that the positive predictive value is 0%.