Week 10

Question 1

Diagnosis:

Answer 1

determining the nature of a disorder by considering the patients signs and symptoms, medical background, etc.

Question 2

Differential diagnosis:

Answer 2

Diagnosis of a condition whole signs and/or symptoms are shared by various other conditions. For example, abdominal pain may be due to multiple different disorders, which need to be ruled out before finding correct diagnosis.

Question 3

There is not always a one-to-one link between a sign or symptom and underlying disorder…..

Answer 3

• One symptoms could indicate multiple disorders

- One disorder could have multiple symptoms

Question 4

Reference test of known high accuracy—>

Answer 4

Gold standard, make sure its valid

Question 5

Diagnostic accuracy study design involving two tests:

Answer 5

Reference and index test

Question 6

Index test - evaluated by the diagnostic accuracy study —>

Answer 6

if index test results agree with the reference test results = diagnostic accuracy of index test

Question 7

In the reference test results: Case = _____ and control = _____

Answer 7

Case = person with health condition
Control = person without health condition

Question 8

In the index test results: positive = _____ and negative = _____

Answer 8

Positive = the person classified as a case
Negative = the person classified as a control

Question 9

Case, control, positive, negative… Which ones line up?

Answer 9

Case and positive, control and negative

Question 10

Diagnostic study design: Level ____ - Diagnostic accuracy study with blinded, independent testing with random or consecutive patients; “consecutive cohort”

Answer 10

2

Question 11

Diagnostic study design: Level _____ - Diagnostic accuracy with non-consecutive patients

Answer 11

III-1

Question 12

Level ___ - Diagnostic case-control study - cases identified from reference test then compared on index test

Answer 12

III-2

- Overestimates accuracy (biased) because case status is already known

Question 13

Level IV diagnostic yield study, has no ……?

Answer 13

Reference list

Question 14

Diagnostic accuracy studies tend to be cross-sectional

- about “___ and ___”, not longitudinal or tracking

Answer 14

here and now

Question 15

Diagnostic tests SHOULD distinguish people who have the condition from others who don’t have it —- that’s ____ discrimination

Answer 15

valid

Question 16

If an index test is valid then:

Answer 16

• All of its positive results will be cases - people who really do have the health condition
• All of its negative results will be controls - people who really don’t have the health condition

Question 17

Biases in diagnostic studies–> incorporation bias…?

Answer 17

When reference tests include the index tests, an obvious design flaw because any measures of diagnostic accuracy will include the agreement of the index test with itself, a measure of reliability rather than validity

Question 18

Biases in diagnostic studies–> verification bias…?

Answer 18

Can happen because of sampling problems. Where sensitivity is over estimated, means that more people are testing positive than should test positive. Or underestimated, where fewer controls are testing negative than should test negative. All together—> too many positive results from the index test because of the bias

Question 19

Continuous , ordered data measured on a scale examples? (must be categorised into cases and non-cases)

Answer 19

height, weight, pain, degrees of flexion, grip strength, etc

Question 20

Categorical, unordered [nominally scaled] data …

Answer 20

• Patients categorised naturally into…
• Cases and controls on reference list
• Positive and negatives on index test

Question 21

Linking reference and index test categories

Answer 21

• Statistical measures of association

- Tests of diagnostic accuracy

Question 22

Sensitivity (Sn):

Answer 22

• Index test ability to detect people with the condition

- Percentage of cases with a positive result

Question 23

Specificity (Sp):

Answer 23

• Index test to ability to identify people without condition

- Percentage of controls with negative result

Question 24

Sensitivity and specificity usually ___ for the same test

Answer 24

differ

Question 25

Positive predictive value (PPV) (not same as sensitivity)

Answer 25

Percentage of positive tests who are cases

Question 26

Negative predictive value (NPV) (not same as specificity)

Answer 26

Percent of negative tests who are controls

Question 27

Sensitivity Sn - how good is index at detecting ____

Answer 27

cases

• HIGH sensitivity finds true positives; few false negatives
• LOW sensitivity misses true positives; many false negatives

Question 28

Specificity Sp - how good is index at detecting _____

Answer 28

controls

• HIGH specificity finds true negatives; few false positives
• LOW specificity misses true negatives; many false positives

Question 29

Positive predictive value PPV - whether positives are ____

Answer 29

cases

• If HIGH, most people who test positive will be cases
• If LOW, most people who test positive will be controls

Question 30

Negative predictive value NPV - whether negatives are ____

Answer 30

controls

• If HIGH, most people who test negative will be controls
• If LOW< most people who test negative will be cases

Question 31

Sensitivity - Do cases test positive??

Answer 31

• Cases should test positive

- Higher percentage, more of the cases test positive

Question 32

Specificity Sp - Do controls test negative??

Answer 32

• Controls should test negative

- Higher percentages, more of the controls test negative

Question 33

Positive predictive value PPV - Are positives cases?

Answer 33

Higher percentage, more of the positives are cases

Question 34

Negative predictive value NPV - Are negatives controls?

Answer 34

• Negatives should be controls

- Higher percentage, more of the negatives are controls

Question 35

Anterior cruciate ligament tears:
______: Gold standard –> arthroscopy or MRI
- expensive, but valid

_____:

• anterior drawer test
• lachmans test
• pivot shift test
• inexpensive, less valid

Answer 35

reference, index

Question 36

Reference and index are _____ concepts, not used in everyday practice

Answer 36

research

Question 37

Ideal way to improve diagnostic accuracy

Answer 37

• Use more valid test
• Higher correlation between index and reference test
• Reduces false positives and false negatives at same cut-off