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Citation:
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Are the results of this diagnostic study valid?
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Was there an independent, blind comparison with a reference (“gold”) standard of diagnosis? |
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Was the diagnostic test evaluated in an appropriate spectrum of patients (like those in whom it would be used in practice)? |
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Was the reference standard applied regardless of the diagnostic test result? |
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Was the test (or cluster of tests) validated in a second, independent group of patients? |
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Are the valid results of this diagnostic study important?
YOUR CALCULATIONS
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Target disorder
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Totals |
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Present |
Absent |
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Diagnostic test result
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Positive
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a
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b
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a+b
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Negative |
c |
d
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c+d |
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Totals |
a+c |
b+d |
a+b+c+d |
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Sensitivity = a/(a+c)
Specificity = d/(b+d)
Likelihood ratio for a positive test result = LR+ = sens/(1-spec)
Likelihood ratio for a negative test result = LR - = (1-sens)/spec
Positive Predictive Value = a/(a+b)
Negative Predictive Value = d/(c+d)
Pre-test probability (prevalence) = (a+c)/(a+b+c+d)
Pre-test odds = prevalence/(1-prevalence)
Post-test odds = pre-test odds ´ LR
Post-test probability = post-test odds/(post-test odds +1)
Can you apply this valid, important evidence about a diagnostic test in caring for your patient?
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Is the diagnostic test available, affordable, accurate, and precise in your setting? |
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Can you generate a clinically sensible estimate of your patient’s pre-test probability (from personal experience, prevalence statistics, practice databases, or primary studies)? · Are the study patients similar to your own? · Is it unlikely that the disease possibilities or probabilities have changed since the evidence was gathered? |
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Will the resulting post-test probabilities affect your management and help your patient? · Could it move you across a test-treatment threshold? · Would your patient be a willing partner in carrying it out? |
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Would the consequences of the test help your patient? |
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