Screening tests Flashcards
Number of patients who need to be treated for ONE patient to benefit
Number needed to treat (NNT)
Equation for NNT
NNT = 1 / ARR
(ARR = Risk(intervention) - Risk(control))
Number of patients who need to be treated for ONE patient to be harmed that would otherwise not have been harmed
Number needed to harm (NNH)
If NNT is negative, then it is this value
Number needed to harm (NNH)
Attributable risk is called this when comparing benefits
Absolute risk reduction (ARR)
Equation for risk reduction / attributable risk
Risk (no treatment) - Risk (treatment)
Time period between disease onset and clinical symptoms that can be picked up by testing
Detectable preclinical period (DPCP)
Validity test for screening test:
Identifying cases of disease
Sensitivity
Validity test for screening test:
Identifying disease-free persons
Specificity
Validity test for screening test:
Person with a positive test has the disease
Positive predictive value (PPV)
Validity test for screening test:
Person with a negative test does not have the disease
Negative predictive value (NPV)
How to calculate sensitivity from 2x2 table
True positive / All disease positive (true positive + false negative)
How to calculate specificity from 2x2 table
True negative / All disease negative (True negative + false positive)
How to calculate PPV from 2x2 table
True positive / All positive (true + false)
How to calculate NPV from 2x2 table
True negative / All negative (true + false)