Unit 03: Screening & Diagnostic Testing (Part 1) Flashcards
What is a bimodal curve?
- A type of distribution, in which there are two peaks.
- In general, most human characteristics are not distributed bimodally.
What is a unimodal curve?
- a type of distribution, in which there is one peak.
What is Validity?
- 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)
What is Reliability?
- 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.
What are the two components of Validity?
- Sensitivity (Sn)
- Specificity (Sp)
What is sensitivity (Sn)?
- 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).
What is specificity (Sp)?
- 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).
As Sn increases, the number of what decreases?
false negatives
As Sp increases the number of what decreases?
false positives
What is True Prevelance (TP)?
the actual proportion of disease (or health outcome) within a population and is usually determined by the results of the gold standard reference test.
What is Appraent Prevelance (AP)?
the observed proportion of disease (or health outcome) within a population which is usually determined by the results of the new test being evaluated.
What is a Positive predictive value (PPV)?
If the test results are positive in this patient, what is the probability that this patient has the disease?
What is a Negative predictive value (NPV)?
If the test result is negative, what is the probability that this patient does not have the disease?
What two things influence the Positive predictive value (PPV)?
- the prevalence of the disease in the population tested
- the specificity of the test being used (when the disease is infrequent)
What is the relationship between Positive Predictive Value and Disease Prevalence?
- the higher the prevalence, the higher the predictive value (and when prevalence increases, NPV decreases.)
What is the relationship between Positive Predictive Value and Test Specificity?
- 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.)
What are the four components of a 2X2 table?
- True Positive (TP)
- True Negative (TN)
- False Positive (FP)
- False Negative (FN)
What’s a False Negative (FN)?
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.)
What’s a False Positive (FP)?
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.)
What’s a True Negative (TN?
If the participant tested negative on the gold standard and negative on the other test (someone that is truly not sick).
What’s a True Positive (TP)?
If the participant tested positive on the gold standard and positive on the other test (someone that truly is sick).
