Stata Lecture 6 Flashcards
What are ‘reference standard’ tests?
Diagnostic tests with highest available accuracy, however they are often expensive, invasive and time consuming
What is sensitivity?
Proportion of people with the disease who will test positive
What is specificity?
Proportion of people without the disease who will test negative
How is sensitivity calculated?
(True positives)/(True positives + False negatives)
How is specificity calculated?
(True negatives)/(True negatives + False positives)
What might affect the sensitivity of a test?
How advanced the disease is
What might affect the specificity of a test?
If people without the disease also show ‘symptoms’ that people with the disease do
What is positive predictive value?
The proportion of people who test positive who actually have the disease
How is PPV calculated?
(true positives)/(true positives + false positives)
What is negative predictive value?
The proportion of people who test negative who actually don’t have the disease
How is NPV calculated?
(true negatives)/(true negatives + false negatives)
What 3 things impact PPV and NPV?
Sensitivity
Specificity
Prevalence of disease
How does prevalence of a disease affect PPV and NPV?
A disease with very high prevalence will have a greater PPV and lower NPV
A disease with very low prevalence will have a lower PPV and greater NPV
