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
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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
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c
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d
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c+d
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Totals
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a+c
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b+d
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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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