True and Apparent Prevalence

Question 1

Prevalence

Answer 1

Proportion (fraction, probability) of cases of disease within a population

Question 2

How do you estimate prevalence?

Answer 2

• select a sample of animals

- use a diagnostic test

Question 3

Apparent prevalence

Answer 3

Test 1000 dogs, record 100 positive tests

- 100/1000 = 10%

Question 4

What are sources of error with apparent prevalence?

Answer 4

• error associated with sampling (address by calculating a confidence interval)
• misclassification error with a diagnostic test –> adjust with Sn and Sp

Question 5

What is the importance of knowing prevalence?

Answer 5

• helps estimate commonness of disease in a population

- what the population’s medical needs will be

Question 6

True prevalence

Answer 6

Takes into account the known inaccuracies of the diagnostic test
- use Sn and Sp

Question 7

What if the sensitivity and specificity were both 1?

Answer 7

True prevalence would be the same as apparent prevalence