Screening Tests

Question 1

Number of patients who need to be treated for ONE patient to benefit

Answer 1

Number needed to treat (NNT)

Question 2

Equation for NNT

Answer 2

NNT = 1 / ARR
(ARR = Risk(intervention) - Risk(control))

Question 3

Number of patients who need to be treated for ONE patient to be harmed that would otherwise not have been harmed

Answer 3

Number needed to harm (NNH)

Question 4

If NNT is negative, then it is this value

Answer 4

Number needed to harm (NNH)

Question 5

Attributable risk is called this when comparing benefits

Answer 5

Absolute risk reduction (ARR)

Question 6

Equation for risk reduction / attributable risk

Answer 6

Risk (no treatment) - Risk (treatment)

Question 7

Time period between disease onset and clinical symptoms that can be picked up by testing

Answer 7

Detectable preclinical period (DPCP)

Question 8

Validity test for screening test:
Identifying cases of disease

Answer 8

Sensitivity

Question 9

Validity test for screening test:
Identifying disease-free persons

Answer 9

Specificity

Question 10

Validity test for screening test:
Person with a positive test has the disease

Answer 10

Positive predictive value (PPV)

Question 11

Validity test for screening test:
Person with a negative test does not have the disease

Answer 11

Negative predictive value (NPV)

Question 12

How to calculate sensitivity from 2x2 table

Answer 12

True positive / All disease positive (true positive + false negative)

Question 13

How to calculate specificity from 2x2 table

Answer 13

True negative / All disease negative (True negative + false positive)

Question 14

How to calculate PPV from 2x2 table

Answer 14

True positive / All positive (true + false)

Question 15

How to calculate NPV from 2x2 table

Answer 15

True negative / All negative (true + false)

Question 16

Does PPV or NPV parallel changes in prevalence?

Answer 16

PPV

Question 17

Does PPV or NPV inversely parallel changes in prevalence?

Answer 17

NPV

Question 18

Tests used to rule out a diagnosis, have a high degree of sensitivity

Answer 18

Screening tests

Question 19

Tests used to rule in a diagnosis, have high degree of specificity

Answer 19

Confirmatory tests

Question 20

Screening tests have a high degree of this

Answer 20

Sensitivity

Question 21

Confirmatory tests have a high degree of this

Answer 21

Specificity

Question 22

How to calculate accuracy from a 2x2 table

Answer 22

(True negative + True positive) / Total

Question 23

How to calculate a positive Likelihood ratio from 2x2 table

Answer 23

Probability of true positive / probability of false positive

Question 24

How to calculate prevalence from 2x2 table

Answer 24

Disease positive / total

Question 25

How to calculate LR+

Answer 25

Sensitivity / (1 - specificity)

Question 26

How to calculate LR-

Answer 26

(1 - sensitivity) / Specificity

Question 27

Of the following, which can NOT be obtained from a 2x2 table:
Prevalence, incidence, sensitivity, specificity

Answer 27

Incidence