Flashcards in 06. Diagnostic Testing Deck (18):

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## Sensitivity

### "True positive rate"; Proportion of people with disease who have a true positive test result; How good a test is at detecting people with disease; Insensitive to prevalence

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## Specificity

### "True negative rate"; Reflects how good the test is at IDing people without disease; unlikely to produce false positives; insensitive to prevalence

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## True positive

### Test positive & disease present

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## False positive

### Test positive & disease absent

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## True negative

### Test negative & disease absent

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## False negative

### Test negative & disease present

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## Likelihood ratio (LR) definition

### The likelihood that a given test result would be expected in a patient with the disease compared to the likelihood that the same result would be expected in a patient without the disease. Can be a positive or negative value.

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## Importance of likelihood ratio

### Useful for assessing the value of performing a diagnostic test. Use the sensitivity & specificity of the test to determine whether the test result will significantly change the probability that a disease exists.

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## LR+ Equation

### [Sensitivity/ (1-specificity)]; Amount by which the pretest probability is INCREASED in pts with POSITIVE test

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## LR+ Interpretation

### SUPPORTS TRUE DISEASE; Should be slightly significant above 1. LR+ >10 causes large shift in posttest probability of disease

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## LR- Equation

### [(1-sensitivity)/specificity]; amount by which the pretest probability of disease is REDUCED in patients with a NEGATIVE test

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## LR- Interpretation

### Supports NO DISEASE; Should be significant

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## LR = 1

### No shift in probability of disease

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## Predictive value importance

### Sensitive to prevalence; indicates what the test MEANS to the patient

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## Positive predictive value

### % of positives that are TRUE POSITIVES; [True positives/All positives]

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## Negative predictive value

### % of negatives that are TRUE NEGATIVES; [True negatives/All negatives]

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## Parallel testing

### Shotgun; Many tests at once. ANY positive is diagnostic. INCREASES SENSITIVITY. Reduces risk from lack of intervention.

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