Duke Health - Module 4

Question 1

How serious is risk of bias?
* Did participating patients constitute a representative sample of those presenting with a diagnostic dilemma?
o The group of patients in which the test was conducted should include patients with a …
o The patients in the study should resemble what might be expected in —

Answer 1

high, medium, and low probability of having the target disease

clinical practice

Question 2

• Did investigators compare the test to an appropriate independent reference standard?
  o The reference (or gold) standard refers to the

Answer 2

commonly accepted proof that the target disorder is present or not present

Question 3

o The reference standard might be (2 examples)

Answer 3

an autopsy or biopsy

Question 4

o The reference standard provides — criteria or a current clinical standard for diagnosis. Sometimes there may not be a widely accepted reference standard. The author will then need to …

Answer 4

objective

clearly justify their selection of the reference test

Question 5

• Were those interpreting the test and other reference standard blind to the other results?
  o To avoid potential bias, those conducting the test …

Answer 5

should not know or be aware of the results of the other test

Question 6

• Did all patients receive the same reference standard irrespective of the results of the test under investigation?
  o Researchers should conduct …
  o Researchers should not be tempted to forgo either test based on …
  o Nor should researchers apply a different reference standard to patients with a — result in the study test

Answer 6

both tests (the study test and the reference standard) on all patients regardless of the results of the test in question

the results of only one of the tests

negative

Question 7

• Sensitivity

Answer 7

o True positive, all disease positives
o Measures the proportion of patients with the disease who also test positive for the disease in this study. It is the probability that a person with the disease will have a positive test result.

Question 8

• Specificity

Answer 8

o True negative, all disease negatives
o Measures the proportion of patients without the disease who also test negative for the disease in this study. It is the probability that a person without the disease will have a negative test result.

Question 9

• Likelihood ratios

Answer 9

o Indicate the likelihood that a given test result would be expected in a patient with the target disorder compared to the likelihood that the same result would be expected in a patient without that disorder.

Question 10

• Sensitivity and specificity are characteristics of the test but do not provide enough information for the clinician to

Answer 10

act on the test results

Question 11

• Likelihood ratios can be used to help adapt the results of a study to specific patients. They help determine the

Answer 11

probability of disease in a patient

Question 12

o Positive LR

Answer 12

o The likelihood ratio for positive results
o LR+ = pos test in patients with disease / pos test in patients without disease

Question 13

o Negative LR

Answer 13

o The likelihood ratio for negative results
o LR- = neg test in patients with disease / neg test in patients without disease

Question 14

• Likelihood ratios can be used to move from

Answer 14

pre-test probability for a disease to post-test probability for the disease
* Fagan’s Nomogram

Question 15

How much do LRs change disease likelihood?
* LR = 1.0
* LR < 2 or LR > 0.5
* LR 2-5 or 0.2-0.5
* LR 5-10 or 0.1-0.2
* LR > 10 or LR < 0.1

Answer 15

o Cause no change at all

o Cause tiny changes

o Cause small changes

o Cause moderate changes

o Cause large changes