Module 11 - Medical Decision Making

Question 1

What is a screening test?

Answer 1

Used to detect disease at earliest stages among asymptomatic persons in general population

Question 2

What is a diagnostic test?

Answer 2

Used to confirm a diagnosis among persons with existing signs or symptoms of illness

Question 3

What is a synonym for validity?

Answer 3

Accuracy

Question 4

What is a synonym for reliability?

Answer 4

Precision

Question 5

What is test validity (aka accuracy)?

Answer 5

How well a test or instrument or procedure measures what it says it is measuring

Question 6

What is internal validity?

Answer 6

The extent to which you are able to say that no other variables except the one you’re studying caused the result.

Question 7

What is external validity?

Answer 7

The extent to which the results of a study are valid for the population from which the sample was drawn (i.e. how generalizable are the results)

Question 8

What are common threats to external validity?

Answer 8

Examples of how you might be wrong in making generalizations. Threats include people, places, times

Question 9

What is reliability?

Answer 9

The degree to which a measurement is immune from random variation

Question 10

What is a false positive and how does it relate to type 1 error?

Answer 10

A person who tests positive but does not have the disease, is equal to type 1 error and also equal to the alpha level set for the test

Question 11

What is a false negative and how does it relate to type 2 error?

Answer 11

A person tests negative but they really do have the disease. This is equal to the type 2 error and is also equal to 1-alpha level. This parameter is known as Beta.

Question 12

Sensitivity

Answer 12

Proportion of individuals with disease who test positive, measure of true positive rate

Question 13

Specificity

Answer 13

Proportion of those without disease who test negative, measure of true negative rate

Question 14

How does false negative rate relate to sensitivity?

Answer 14

False negative rate = 1 - sensitivity

Question 15

How does false positive rate relate to specificity?

Answer 15

False positive rate = 1 - specificity

Question 16

Which type of test is used for screening?

Answer 16

A very sensitive test is used to screen for disease or to rule out the disease

SNNOUT: if a person tests negative using a highly sensitive test, you can rule out that disease for that person

Question 17

Which type of test is used for diagnostic purposes?

Answer 17

A very specific test shoul dbe used to confirm or rule in a disease.

SPPIN: a person who tests positive using a highly specific test should be considered as having that disease

Question 18

What tool would you use to determine the cutoff point for sensitivity and specificity?

Answer 18

A ROC curve - each point on curve corresponds to pair of sensitivity and specificity at that cutoff. The pair should be chosen based on whether you are screening or diagnosing.

Question 19

What is PPV?

Answer 19

The probability that a person actually has the disease given a positive test result

Question 20

What is NPV?

Answer 20

The probability that a person does not have the disease given a negative test result

Question 21

What is the prevalence?

Answer 21

The proportion of individuals with disease to the total population

Question 22

If the prevalence of a disease is high, what effect will this have on the PPV and NPV?

Answer 22

PPV will be high, NPV will be low

Question 23

If the prevalence of a disease is low, what effect will this have on the PPV and NPV?

Answer 23

PPV will be small

NPV will be large