Diagnostic Tests

Question 1

Three Purposes of Diagnostic Tests

Answer 1

1) Focus Examination in a particular area of the body; leads you to the problem
2) Identify potential problems that require referral
3) Assist in classification process and ultimately GUIDE treamtment

Question 2

Test Threshold (definition)

Answer 2

Probability below which a test will NOT be performed bc the possibility of a certain diagnosis is so unlikely

Question 3

Treatment Threshold (def)

Answer 3

Probability above which a test will not be performed bc the possibility of a certain diagnosis is SO likely that immediate treatment should be performed

Question 4

Measurement Reliability (def)

Answer 4

Test produces STABLE RESULTS over time

Question 5

Measurement Validity (def)

Answer 5

Test CORRECTLY CAPTURES what it is supposed to be testing

Question 6

Increased validity =

Answer 6

increased chance that the test results are free from bias and error and are believable

Question 7

Test results are composed of: (2)

Answer 7

“true value” and “error”

-Want to minimize error during testing!

Question 8

Error in a test may be due to: (4)

Answer 8

• The subject
• The observer
• The instrument
• The environment

Question 9

Statistics commonly used to evaluate reliability of diagnostic tests: (5)

Answer 9

• Standard Error of Measurement (SEM)
• Pearson’s Product Moment Correlation (r)
• Intraclass Correlation Coefficient (ICC)
• Spearman’s Rho (p)
• Kappa (k)

Question 10

Two types of validity commonly associated with Daignostic Tests

Answer 10

1) Face Validity
2) Criterion Related Reliability
- May be evaluated through mathematical calculations using a 2x2 CONTINGENCY TABLE

Question 11

2x2 Contingency Table is the basis for calculating:

Answer 11

Sensitivity and Specificity

Question 12

Face Validity (def)

Answer 12

Does the test look like it’s measuring what it’s supposed to be measuring?

Question 13

Criterion-related validity (def)

Answer 13

Relates diagnostic test to a gold standard

Question 14

Sensitivity (def)

Answer 14

Capability of classifying individuals with a condition of interest (a true positive)

Question 15

Mathematical Equation for Sensitivity (from Cont. Table)

Answer 15

(True positives)/(True positives+ False Negatives)

aka a/(a+c)

Question 16

SnNout

Answer 16

• If you have a highly sensitive test and a negative result- RULE OUT disorder!
• meaning True positives are high, so if you get a negative result it’s probably a true negative

Question 17

Specificity (def)

Answer 17

Capability of correctly classifying individuals WITHOUT the disorder (aka true negatives)

Question 18

Mathematical Equation for Specificity

Answer 18

(True Negatives)/(False Positives + True Negatives)

Aka d/(b+d)

Question 19

SpPin

Answer 19

• If you have a highly specific test and a positive result- RULE IN the disorder!
• Meaning true negatives are high so likelihood of false negatives is low

Question 20

Receiver Operating Curve (def)

Answer 20

Graphic depiction of different test scores in relation to the number of true positive and false positive test results, obtained at each cut point

Question 21

What does the area under the Receiver Operating Curve Represent?

Answer 21

• The true and false positives for each score obtained on the diagnostic test for each cut point
• Higher true positive rate = bigger area under the curve

Question 22

Positive Predictive Value (def)

Answer 22

Ability of a diagnostic test to correctly determine the proportion with the diease from all of the patients who tested positive on a diagnostic test

Question 23

Negative Predictive Value (def)

Answer 23

Ability of a diagnostic test to correctly determine the proportion of patients without the disease from all of the patients who tested negative on the diagnostic test

Question 24

Positive Likelihood Ratio (LR+)

Answer 24

• Likelihood that a positive test result was obtained in a patient with the disorder as compared to a patient without the disorder
• HIGHER numbers are better!!

Question 25

Negative Likelihood Ratio (LR-)

Answer 25

• Likelihood that a negative test result was obtained in a patient with the disorder as compared to a patient without the disorder
• LOWER numbers are better!

Question 26

Best measure of a diagnostic test is:

Answer 26

Likelihood Ratios

Question 27

Three Advantages to using Likelihood Ratios in regards to diagnostic tests:

Answer 27

1) Ratios can be calculated for all levels of test results
2) Not dependent on prevalence of the condition in the population
3) Can be used with individuals and groups