Screenings in medicine

Question 1

Sensitivity

Answer 1

How well a test can detect presence of disease when in fact the disease is present
Proportion of time that a test is positive in a patient that does have the disease
Highly sensitive test has low false negative rate

Question 2

Sensitivity equation

Answer 2

Sensitivity= TP/(TP+FN) x 100
Sensitivity= TP/ All diseased x100

Question 3

Specificity

Answer 3

How well a test can detect absence of a disease when in fact the disease in absent
Proportion of time that a test is negative in a patient that does not have disease
Highly specific test has low false positive rates

Question 4

Specificity equation

Answer 4

Specificity= TN/ (TN+FP) x 100
Specificity= TN/ All not diseased x100

Question 5

Positive predictive value and equation

Answer 5

How accurately a positive test predicts the presence of disease
Proportion of true positives in patients with a positive test
PPV= TP/ (TP+FP) x100
PPV= TP/ All positive tests x100

Question 6

Negative predictive value

Answer 6

How accurately a negative test predicts the absence of disease
Proportion of true negatives in patients with a negative test
NPV= TN/ (TN+FN) x100
NPV= TN/ All negative tests x100

Question 7

Diagnostic accuracy/diagnostic precision

Answer 7

Proportion of total screenings that a patient is correctly identified as either having a disease or not having a disease with either a positive or negative test, respectively

Question 8

DA/DP equation

Answer 8

DA= (TP+TN) / (TP+FP+TN+FN) x100
DA= (TP+TN) / All patients x 100

Question 9

Likelihood ratio positive

Answer 9

Probability of a positive test in the presence of disease / probability of a positive test in the absence of disease
Sensitivity / (1-specificity)

Question 10

Likelihood ratio negative

Answer 10

Probability of a negative test in the presence of disease / probability of a negative test in the absence of disease
(1-sensitivity) / specificity

Question 11

LR+ number to be beneficial

Answer 11

LR+ should be >10 to demonstrate the test is more beneficial

Question 12

LR- number to be beneficial

Answer 12

LR- should be <0.1 to demonstrate the test is more beneficial

Question 13

Validity

Answer 13

Ability to accurately discern between those that do and those that do not have the disease

Question 14

Internal validity

Answer 14

Extent to which results accurately reflect what was being assessed

Question 15

External validity

Answer 15

Extent to which results are applicable to other populations

Question 16

Reliability

Answer 16

Ability to give the same result on repeated uses

A valid test is always reliable, yet a reliable test is not always valid