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20 Cards in this Set
- Front
- Back
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What is the Coefficient of Variation? |
CV = [SD/mean] x 100 % |
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What is analytical and biological variation? |
Analytical variation: small differences in assay time,pipetting errors.
Biological variation: human physiology can changefrom day to day (posture,exercise, stress, nutrition). |
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How do you determine whether there is a critical difference? |
Difference between results is significant at 95% confidence if difference is 2.8x the SD of test
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How is SD of test calculated? |
Square root of [(SD^2(analytical) + SD^2(biological)]
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What does test specificity and sensitivity measure? |
Test utility (not to be confused with terms to describe analytical properties of tests) |
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What is the formula for specificity? |
TN/[all without disease (FP + TN)] x 100% |
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What is the formula for sensitivity? |
TP/[all without disease (TP + TN)] x 100% |
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What does 100% specificity show? |
All disease free individuals are tested as suchwith no false positives |
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What does 100% sensitivity show? |
All diseased individuals are tested as suchwith no false negatives |
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How does a factor that increases specificity effect sensitivity? |
As the reference range and disease range overlap, decreases sensitivity |
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When is high specificity preferable? |
Reducing FP Testing patients for a new treatment, only patients with the condition are treated underthe new regime All disease free individuals are found but not all diseased individuals are |
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When is high sensitivity preferable? |
Reduces FN Harmful conditions, false positive identifiedthrough further testing All diseasedindividuals are found but some non-diseased individuals are misdiagnosed. |
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Formula for test efficiency |
Both equally important TP+TN/Total number of tests x 100% |
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What is disease prevalence? |
Proportion of a population that are positive for a given disease
TP+FN/(TP+FN+TN+FP) x 100% |
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What does low prevalence and specificity <100% indicate? |
Many FP |
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What is a predictive value? |
The ability of a test to correctly assign patients to thediseased or non-diseased category
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Predictive Value for a Positive Result |
PV+ve =TP/(TP + FP) x 100 % Describes the percentage of all positive results that are truepositives. Important if a treatment regime for FP would be dangerous |
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Predictive Value for a Negative Result |
PV-ve =TN/(FN +TN) x 100 % Describes the percentage of all negative results that are truenegatives. Screening tests for a new treatment regime should have ahigh PV-ve i.e. tests are highly sensitive. |
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What is specificity? |
Ability of a method to determine only the desired analyte AKA True negative rate |
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What is sensitivity? |
Smallest single result that can bedistinguished from a true blank AKA True positive rate |
