Diagnostic Accuracy: Statistical Tools to Enhance Clinical Decision Making

Question 1

reliability

Answer 1

produces precise, accurate & reproducible information

Question 2

diagnostic accuracy

Answer 2

ability to discriminate between patients with or without a specific disorder

Question 3

pretest probability

Answer 3

likelihood that a patient exhibits a specific disorder before the physical exam starts
uses prevalence rates utilized or clinical demographics, medical history, results of previous tests, clinician expertise, expressed as % or qualitative

Question 4

posttest probability

Answer 4

likelihood that a patient has a specific disorder after the clinical exam test has been performed

Question 5

what is nominal data?

Answer 5

groupings/place holder

Question 6

what is ordinal data?

Answer 6

quantities that have a natural order, but can’t state with any certainty whether intervals between values are equal

Question 7

for nominal & ordinal data what is kappa coefficient (k)?

Answer 7

measure of agreement (%) between two or more individuals
-kappa = measure of agreement after chance has been removed
-weighted Kappa used if more than 2 categories exist
-always < 1.0
( <0.50 = poor reliability 0.50-0.75= moderate reliability. >0.75= good reliability )

Question 8

what is interval data?

Answer 8

order with equal intervals but without an absolute zero (Ex temp)

Question 9

what is ratio data?

Answer 9

order with equal intervals and an absolute zero point (Ex ROM)

Question 10

what does it mean if a test has sensitivity?

Answer 10

true positive rate
a sensitive test when negative test will certainly rule a patient out

Question 11

what does it mean if a test has specificity?

Answer 11

true negative rate
specific test when a positive result definitely rules a patient in

Question 12

What is used to find interval and ratio data correlation coefficient?

Answer 12

Pearson (r)
- analyzes association between 2 measurements
-hypothesis: there is or is not an association between the variables
-analyzes magnitude & direction of associate ranging -1 to 1
- negative values indicate an inverse relationship
- positive values indicate a direct relationship
- zero demonstrates no relationship

Question 13

what is used for interval and ratio data?

Answer 13

ICC (intraclass correlation)
investigates the amount of variance between 2 or more repeated measures
based on the number of raters and specific measurement obtained

Question 14

what is spectrum bias?

Answer 14

may be influenced by prevalence or total instances of a diagnosis in the population at a given time, sex ratios, or severity of the disease

Question 15

what is a positive predictive value?

Answer 15

estimates the likelihood that a patient with a (+) test result actually has the disease
-a higher PPV indicates that a (+) result is strong indicator that the patient has the diagnosis

Question 16

what is a negative predictive value?

Answer 16

estimates the likelihood that a patient with a (-) test result actually does not have the diagnosis
- a high NPV indicates that a (-) result is a strong indicator that the patient does not have the disease

Question 17

what is likelihood ratio?

Answer 17

• a test result is valuable only if it alters the pretest probability that a patient has a disorder
  -sensitivity & specificity are combined to indicate this shift give a certain test result
  -clinical decision making is guided by this statistic

Question 18

Easy to remember LR’s

Answer 18

• 2 & 1/2 (small shift)
• 5 & 1/5 (moderate shift)
• 10 & 1/10 (large shift)

Question 19

how do you judge the quality of a test?

Answer 19

QUADAS - quality assessment of diagnostic accuracy studies

Question 20

what does a positive likelihood ration (LR) indicate?

Answer 20

shift in probability that favors the existence of the disorder >1 LR = increase the odds of a disorder given a positive test