Diagnostic accuracy Flashcards
Define diagnostic accuracy?
The potential of a test to correctly detect the presence or absence of a disease, therefore is the proportion of true results
What is indicated by a positive or negative result of a diagnostic test?
Positive result indicates presence of disease
Negative result indicates absence of disease
In a perfect diagnostic test, which 2 outcomes are not possible?
False negative
False positive
What are the 4 assumptions when estimating accuracy of a new diagnostic test?
The gold standard (reference) has 100% sensitivity, so accurately diagnoses disease
Disease is dichotomous: only has 2 possible values, which are present/absent
Diagnostic test is dichotomous, so only results are positive or negative
Rationale (underlying reason) for the new diagnostic test is primarily to detect disease
What is meant by dichotomous?
Only 2 possible variables
What is specificity of a diagnostic test?
Probability of a test to designate an individual without disease as negative (True negative)
How do you calculate the specificity of a diagnostic test?
Dividing number of true negative results by total number of no disease cases
What is the sensitivity of a diagnostic test?
Probability of a test to designate an individual with disease as positive (True positive)
How do you calculate sensitivity of a diagnostic test?
Dividing number of true positive results by total number of disease cases
What is the positive predictive value of a diagnostic test?
Chance that positive result is correct
How do you calculate the PPV of a diagnostic test?
Calculated by dividing number of true positive results by total number of positive results
What is the negative predictive value of a diagnostic test?
Chance that negative result is correct
How do you calculate the NPV of a diagnostic test?
Calculated by dividing number of true negative results by total number of negative results
In this diagram, what is the meaning of the black and clear dots?
Black dots: Individual with disease
Clear dots: Individual without disease
In this diagram, what is the meaning of the red and blue squares?
Red square: positive result
Blue square: negative result
