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| Epidemiology |
Prevalence / Pre-Test Probability = | A+C A+B+C+D | What percentage of the population has the disease, or the likelihood of an individual patient having the disease? |
|---|---|---|
Sensitivity = | A A+C | How likely is the test to pick up the disease (correctly) if it is present? |
Specificity = | D B+D | How likely is the test to be negative (correctly) if the patient does not have the disease? |
Positive Predictive Value = | A A+B | What is the probability of there being disease in a patient with a positive test? |
Negative Predictive Value = | D C+D | What is the probability of there not being disease in a patient with a negative test? |
Positive Likelihood Ratio = | A A+C B B+D |
How many times more will the test be positive in patients with the disease than in patients who do not have the disease? |
Negative Likelihood Ratio = | C A+C D B+D |
How many times more will the test be negative in patients without the disease than in patients who do have the disease? |
Positive Posttest Probability = | Pretest Probability x Positive Likelihood Ratio | What is the likelihood that there is actually disease in this patient? |
Negative Posttest Probability = | Pretest Probability x Negative Likelihood Ratio | What is the likelihood that there is not actually disease in this patient? |
Prevalence = | # of people with a disease at a point in time # of people at risk (in population) at that time | How common is this condition at a given time in this population? |
Incidence = | # of new cases of a disease over a time period # of people at risk (in population) during that period | How often does this disease get diagnosed in this population? |