Diagnostic Test Accuracy

Question 1

What are DTAs?

Answer 1

Studies used to tell us about the accuracy of medical tests

Question 2

When is a test useful?

Answer 2

When it changes the ability to predict whether a patient has a condition or not

Question 3

What effect should a test result have on diagnosis?

Answer 3

It should alter the probability of diagnosing the condition

Question 4

Why can’t one assume that the evaluated test accuracy is the same in different contexts, even if the same diagnostic test is used?

Answer 4

A change of context results in a change of accuracy and change of probability of outcome of the diagnostic test

Question 5

Why should diagnostic tests be evaluated?

Answer 5

To avoid adoption of non-useful, non-beneficial or harmful diagnostic tests
To choose the most cost-effective of the useful diagnostic tests

Question 6

What are the two criteria that diagnostic tests have to meet to be implemented?

Answer 6

To be proven as safe
To be proven to measure what they say they measure

Question 7

What is important factor is not required to be proven when a diagnostic test is implemented?

Answer 7

The usefulness of the test in diagnosis

Question 8

What evidence is not required when a diagnostic test is implemented?

Answer 8

The overall benefit of the diagnostic test
How the diagnostic test is best used

Question 9

What are some consequences of using inappropriate diagnostics?

Answer 9

Anxiety, discomfort and pain
Unnecessary further investigations
Waste of money
False positive results, which cause unnecessary stress and investigation
False negative results, which causes false reassurance and allows the disease to progress unnoticed

Question 10

Other than different accuracy, give some positive ways in which diagnostic tests can impact on patient outcomes

Answer 10

Safer, easier to perform, faster results, less invasive,

Question 11

What is required for a diagnostic test to have potential value?

Answer 11

It must be evaluated as accurate

Question 12

Give three reasons why DTA studies are useful

Answer 12

They are readily available, unlike RCTs
They do not required prohibitively big sample sizes
Answers are obtained quickly

Question 13

What are the two dimensions of test accuracy?

Answer 13

Sensitivity and specificity

Question 14

What does sensitivity measure?

Answer 14

The proportion of individuals with the disease

Question 15

What does specificity measure?

Answer 15

The proportion of individuals without the disease who have negative results (true negative)

Question 16

What is the inverse of sensitivity?

Answer 16

False negative rate

Question 17

What is the false negative rate?

Answer 17

The proportion of individuals with the disease but a negative test

Question 18

What is the inverse of specificity?

Answer 18

False positive rate

Question 19

What is the false positive rate?

Answer 19

The proportion of individuals without the disease but with a positive test

Question 20

What acronym gives the DTA evaluation components?

Answer 20

PITR

Question 21

What does the P stand for in P?

Answer 21

Participants or population

Question 22

Give two examples of things which would fall under the participants/population component of DTA evaluation

Answer 22

Presentation
Prior tests

Question 23

What does the I stand for in PITR?

Answer 23

Index test

Question 24

What is the index test?

Answer 24

The new diagnostic test which is being evaluated

Question 25

What must be considered when evaluating the index test?

Answer 25

Whether the test is affected by the conductor or skill of the officer Whether the test is affected by technology

Question 26

What does the T stand for in PITR?

Answer 26

Target disorder

Question 27

What is the Target disorder?

Answer 27

The condition that we want the index test to indentify

Question 28

What does the R stand for in PITR?

Answer 28

Reference standard

Question 29

What is a reference standard?

Answer 29

The most accurate method available to detect the target disorder

Question 30

What statistical check must be done is different reference standards are used for index positive and index negative patients?

Answer 30

It must be assessed whether there is a statistically significant difference between the two reference standard tests

Question 31

What role does the reference standard play?

Answer 31

It is a control

Question 32

What is Blinded Cross Classification?

Answer 32

A comparison of the index test and the reference standard test results for detection of a target disorder

Question 33

What are the three source of bias which can arise in DTA evaluation?

Answer 33

Spectrum bias, review bias, verification bias

Question 34

What is spectrum bias?

Answer 34

Purposefully excluding 'difficult to diagnose' patients

Question 35

What effect does spectrum bias have on the DTA evaluation?

Answer 35

The index test appears more accurate at diagnosing than it is

Question 36

How can spectrum bias be avoided?

Answer 36

Clear descriptions of the characteristics of the population Avoidance of inappropriate exclusions

Question 37

What is review bias?

Answer 37

When the interpretation of an index test is not independent and blind to the reference standard

Question 38

What effect does review bias have on the DTA evaluation?

Answer 38

It makes the index test seem more accurate than it is

Question 39

How can review bias be avoided?

Answer 39

Ensure interpretation of the index test was independent and blinded to interpretation of the reference standard, and vice versa

Question 40

What is verification bias?

Answer 40

The tendency not to give the reference standard test to patients who were negative on the index test, because the reference

Question 41

What is verification bias?

Answer 41

The tendency not to give the reference standard test to patients who were negative on the index test, because the reference standard is more invasive

Question 42

How can verification bias be avoided?

Answer 42

Ensure all patients have both the index test and reference standard test, regardless of result

Question 43

What is the effect of verification bias on the DTA evaluation?

Answer 43

Over/underestimation of the index test accuracy

Question 44

What four questions need to be asked to apply the results of a DTA evaluation/what factors contribute to the impact of test use on patient outcomes?

Answer 44

Was there a clear study question? Is the study population similar to patients in my practice? Can the index test be applied in the same way in my healthcare setting? Does the definition of the target condition match the condition I want to identify in my practice?

Question 45

What are the four steps to critically appraising a DTA study?

Answer 45

Construct a diagnostic 2*2 table Assess sensitivity and specificity Assess precision for the estimates of accuracy Evaluate consequences for patients

Question 46

What is sensitivity (in a DTA)?

Answer 46

The proportion of true positive results in individuals with the target condition

Question 47

How is sensitivity calculated?

Answer 47

True positive results/True positive results + False negative results

Question 48

What does sensitivity indicate in terms of usefulness of the test?

Answer 48

How good a test is at ruling out a condition

Question 49

What does sensitivity indicate in terms of false results?

Answer 49

The magnitude of false negatives

Question 50

How can sensitivity be expressed in terms of probability?

Answer 50

The probability that a patient has a positive test, given that they have the disease

Question 51

A negative test with high sensitivity will be better at doing what?

Answer 51

Ruling out a condition

Question 52

When is a highly sensitive test less reliable?

Answer 52

When the test result is positive

Question 53

What does a highly sensitive test have fewer of?

Answer 53

False negatives

Question 54

If a patient is negative on an index test with high sensitivity, what does this mean statistically?

Answer 54

They are statistically more likely to be a true negative

Question 55

What is specificity (in a DTA)?

Answer 55

The proportion of true negative results in those without the target condition

Question 56

How is specificity calculated?

Answer 56

True negative results/True negative results + False positive results

Question 57

What does specificity indicate in terms of usefulness of a test?

Answer 57

How good a test is at ruling in a condition

Question 58

What does specificity indicate in terms of false results?

Answer 58

The magnitude of false positives

Question 59

How can specificity be expressed in terms of probability?

Answer 59

The probability that the result is negative, given that the patient is well

Question 60

A positive test with high specificity will be better at doing what?

Answer 60

Ruling in a condition

Question 61

When is a highly specific test less reliable?

Answer 61

When the result is negative

Question 62

What does a highly specific test have fewer of?

Answer 62

False positives

Question 63

If a patient is positive on an index test with high specificity, what does this mean statistically?

Answer 63

They are more likely to be a true positive

Question 64

When is a test considered uninformative?

Answer 64

When specificity or sensitivity are below 50%

Question 65

What is used to assess the precision of an estimate of accuracy of a diagnostic test?

Answer 65

Confidence intervals

Question 66

Give 3 consequences of false positives for patients

Answer 66

Unnecessary intervention with associated risks Unnecessary stress and anxiety Waste of money and time

Question 67

Give 3 consequences of false negatives for patients

Answer 67

Delayed diagnosis Disease progression Need for more invasive intervention later