Screening

Question 1

What is sensitivity?

Answer 1

how well a test can detect presence of disease when a disease is present. It also the proportion of TIME that a test is positive in a patient that does have aidease.

Question 2

How is sensitivity calculated?

Answer 2

TP/(TP+FN) x 100 or TP/(all diseased) x 100

Question 3

What is specificity?

Answer 3

How well a test can detect the ABSENCE of disease when the disease is absent. It is also the proportion of time that a test is negative in a patient that does not have the edisease.

Question 4

How is specificity calculated?

Answer 4

TN/(TN+FP) x 100% or TN/(all not idseased) x 100

Question 5

What do specificity and sensitivity have in common?

Answer 5

neither terms are predictive in an individual patient (properties of the test)

Question 6

What is the positive predictive value (PPV)?

Answer 6

how accurately a positive test predicts the presence of disease. It is the percentage of TP’s in patients with a positive test (correct prediction).

Question 7

How is PPV calculated?

Answer 7

TP/(TP+FP) x 100% or TP/(all positive tests) x 100%

Question 8

`What is negative predictive value (NPV)?

Answer 8

how accurately a negative test predicts the absence of disease.. It is the percentage of TN’s in patients with a negative test (correct prediction).

Question 9

How is NPV calculated?

Answer 9

TN/(TN+FN) x 100% or TN/(all negative tests) x 100

Question 10

What is diagnostic accuracy/diagnositic precision?

Answer 10

Proportion of time that a patient is correctly lidentified as either having a disease or not having a diasease with a positive or negative test, respectivetly.

Question 11

How is diagnostic accuracy/diagnostic precision calculated?

Answer 11

DA/DP = (TP + TN) / (TP+FP+FN+TN) x 100 or TP+TN/(all patients) x 100%

Question 12

What are likelihood ratios?

Answer 12

Ratio of the probability of a given test result for a presron with the disease divided by the probability of the same test result without the disease. It can be caulculated fro both positive and negative test results.

Question 13

What is the likelihood ratio positive?

Answer 13

probability of a positive test in either the presence or absence of a disease.

Question 14

How is the likelihood ratio positive calculated?

Answer 14

A/(A+C) / B/(B+D)

Question 15

What is the likelihood ratio negative?

Answer 15

the probaiblity of a negative test in the presence or absence of disease.

Question 16

How is likelihood ratio negative calculated?

Answer 16

C/(A+C) / D/(B+D)

Question 17

In order for a test to be beneficial, what should the value of LR+ be?

Answer 17

> 10

Question 18

In order for a test to be beneficial, what should the value of LR- be?

Question 19

What is the receiver operator curve?

Answer 19

A curve that shows the relationship between sensitivity and specificity for tests with numerical continous outcomes.

Question 20

What is validity?

Answer 20

Ability to accurately discern between those that do and thosse that do not have the disease; e.g. telling the truth.

Question 21

what is internal validity?

Answer 21

extent to which results accurately reflect what was being assessed (true situation of the study population().

Question 22

What is external validity?

Answer 22

extent to which the results are applicable to to the populations (not included in the original study, also known as generalizibility).

Question 23

What is reliability?

Answer 23

ability of a test to give the same result on repeated uses. A test may be reliable, but not always valid (e.g. you can always hit the outside of the ring when playing darts, but it is not valid because you are not hitting the center).