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24 Cards in this Set
- Front
- Back
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What is Sensitivity?
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= proportion of patients who have disease who test positive
= true positives / (true positives + false negatives) |
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What is Specificity?
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= proportion of patients who do not have the disease who test negative
= true negatives / (true negatives + false positives) |
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Sensitive tests...
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Rule Out (snOUT)
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Specific tests...
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Rule In (spIN)
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Receiver Operating Curce (ROC)
High Cutoff = Medium Cutoff = Low Cutoff = |
High = Specific, nonSensitive
Medium = between Low = non-specific, Sensitive |
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Positive Predictive Value
= post test probability |
Probability of Having the Disease Given a Positive Result
= TP / (FP + TP) |
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Negative Predictive Value
= post test probability |
TN / (FN + TN)
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How does the fact that a disease is rare (low pretest probability) affect the interpretation of a positive test?
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A positive test may actually be more likely to come from a healthy person
FP > TP !!! Anxiety |
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What is the Treatment Threshold?
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When the post-test probability is high enough, Treat.
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What is the Test Threshold?
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When the post-test probability is low enough, Stop Testing.
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What is likelihood ratio?
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probability of result in those who have the disease / probability of result in those who do have the disease
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What is likelihood ratio if test is positive?
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Sensitivity / (1 - Specificity)
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What is likelihood ratio if test is negative?
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(1 - sensitivity) / specificity
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The Nomogram: why do you use it?
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Draw a line from the pre-test probability through the likelihood ratio to get to the post test probability
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What magnitudes of LRs are useful?
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> 5-10 for rule in
< 0.1 - 0.2 for rule out |
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What is Efficacy?
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= usefulness in ideal circumstances
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What is Effectiveness?
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= usefulness in usual circumstances
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What is a surrogate outcome?
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An outcome that stands in for desired clinical outcome, e.g. increased CD4 count in ARVs or decreased cholesterol in preventing MIs
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Is fever a good surrogate outcome for predicting death from sepsis?
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No. Can give acetominaphen to reduce fever but death will happen regardless.
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What is a Type I error?
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Probability of finding difference in populations despite absence of difference
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What is a Type II error?
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Probability of finding no difference when difference exists
= beta. Power = 1 - beta. |
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What is NNT?
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Number needed to treat.
NNT = 1 / ARR |
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What are good cutoffs for NNT?
Treatment? Prophylaxis? |
Tx = 2 - 5
Prophylaxis = 10 - 100 |
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What is NNH?
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NNH = 1 / ARI
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