Unit 03: Screening & Diagnostic Testing (Part 1)

Question 1

What is a bimodal curve?

Answer 1

• A type of distribution, in which there are two peaks.
• In general, most human characteristics are not distributed bimodally.

Question 2

What is a unimodal curve?

Answer 2

• a type of distribution, in which there is one peak.

Question 3

What is Validity?

Answer 3

• how accurately it measures an individual’s overall infection status or disease state.
• high validity is indicated when the average of all the test results (half-way point of the curve) is near the true value.
• When a test has perfect validity we refer to that test as the “gold standard.” (when there are no misdiagnoses)

Question 4

What is Reliability?

Answer 4

• the variation in the test results after it has been repeated numerous times or the deviation from the average result.
• represented by the width of the curve.

Question 5

What are the two components of Validity?

Answer 5

1. Sensitivity (Sn)
2. Specificity (Sp)

Question 6

What is sensitivity (Sn)?

Answer 6

• the proportion of diseased people who were correctly identified as “positive”.
• if a test is highly sensitive (Sn), and you get a negative test result, you can be confident in ruling the disease out (i.e., the individual does not have the disease, few/no false negatives).

Question 7

What is specificity (Sp)?

Answer 7

• the proportion of nondiseased people who are correctly identified as “negative”.
• if a test is highly specific (Sp), and you get a positive test result, you can be confident in ruling the disease in (i.e., the individual has the disease, few/no false positives).

Question 8

As Sn increases, the number of what decreases?

Answer 8

false negatives

Question 9

As Sp increases the number of what decreases?

Answer 9

false positives

Question 10

What is True Prevelance (TP)?

Answer 10

the actual proportion of disease (or health outcome) within a population and is usually determined by the results of the gold standard reference test.

Question 11

What is Appraent Prevelance (AP)?

Answer 11

the observed proportion of disease (or health outcome) within a population which is usually determined by the results of the new test being evaluated.

Question 12

What is a Positive predictive value (PPV)?

Answer 12

If the test results are positive in this patient, what is the probability that this patient has the disease?

Question 13

What is a Negative predictive value (NPV)?

Answer 13

If the test result is negative, what is the probability that this patient does not have the disease?

Question 14

What two things influence the Positive predictive value (PPV)?

Answer 14

1. the prevalence of the disease in the population tested
2. the specificity of the test being used (when the disease is infrequent)

Question 15

What is the relationship between Positive Predictive Value and Disease Prevalence?

Answer 15

• the higher the prevalence, the higher the predictive value (and when prevalence increases, NPV decreases.)

Question 16

What is the relationship between Positive Predictive Value and Test Specificity?

Answer 16

• a change in specificity has a greater effect on predictive value than a comparable change in sensitivity. (If we were dealing with a high-prevalence disease, the situation would be different.)

Question 17

What are the four components of a 2X2 table?

Answer 17

1. True Positive (TP)
2. True Negative (TN)
3. False Positive (FP)
4. False Negative (FN)

Question 18

What’s a False Negative (FN)?

Answer 18

If an individual tested positive on the gold standard, but negative on the other test (the new test indicated they didn’t have the disease, although we know from the gold standard that they truly did.)

Question 19

What’s a False Positive (FP)?

Answer 19

If an individual tested negative on the gold standard, but positive on the other test (the new test indicated they had the disease, although we know from the gold standard that they truly did not.)

Question 20

What’s a True Negative (TN?

Answer 20

If the participant tested negative on the gold standard and negative on the other test (someone that is truly not sick).

Question 21

What’s a True Positive (TP)?

Answer 21

If the participant tested positive on the gold standard and positive on the other test (someone that truly is sick).