EBP

1.10

Prevalence

Proportion of people with the target condition in the population

Overall Test Accuracy

Proportion of test results that are correct

Sensitivity

Proportion of people with the target condition who have a positive test result

Probability that someone with the target condition will get a positive test result

Helps us to rule OUT conditions

Specificity

Proportion of people without the target condition who have a negative test result

Probability that someone who does not have the target condition will get a negative result

Helps us rule IN conditions

Positive Predictive Value

Estimates the likelihood that a person who tests positive actually has the disease

The proportion of people with a positive test result who have the condition

Negative Predictive Value

Indicates the probability that a person who tests negative is actually disease free

The proportion of people with a negative test result who do not have the condition

SpPin

With high specificity, a positive test rules IN the diagnosis

SnNout

With high sensitivity, a negative test rules OUT the diagnosis

Pretest Probability

Aka prevalence, prior probability of the disorder

What we think might be the problem before we perform any formal testing

A “best guess” or clinical impression

Posttest Probability

The probability of having the target condition after the results of a test are known

Can be calculated using pre-test probability and the Likelihood Ratio associated with a given test result or set of test results

What does it mean to have high posttest probability?

The test was good; we can confirm the diagnosis

What does it mean to have a low posttest probability?

We must abandon the diagnosis

Positive Likelihood Ratio (LR+)

Relative likelihood of a (+) test result in someone with the condition as compared to someone without the condition

Factor by which the odds of having the condition are increased following a (+) test result

Higher LR+ helps us rule IN

Negative Likelihood Ratio (LR-)

The relative likelihood of a (-) test result in someone with the condition as compared to someone without the condition

The factor by which the odds of having the condition are decreased by a (-) test result

Lower LR- helps us rule OUT