MUSM Libraries: Evaluating a DIAGNOSTIC TEST STUDY article

Appraise | Likelihood ratios | Finding articles


Appraise

What did they do? (Methods)

1. Was there an independent, blind comparison with reference to a “gold” standard?
2. Was the test evaluated in an appropriate spectrum of patients (like those in whom we would use it in practice)?
3. Was the reference standard ascertained regardless of the diagnostic test result?

What was the answer? (Results)

1. What likelihood ratios are associated with the range possible test results?

What did they say about the answer? (Conclusion)

1. Do the results of the study support the author/s conclusions?

2. Does the conclusion reflect the discussion?

3. Are there study limitations, and do these impact the conclusions?

What do I do with this information?

1. Will the reproducibility of the test result and its interpretation be satisfactory in my setting?

2. Are the results applicable to my patient?

4. Will patients be better off as a result of the test?

5. Are the benefits woth the potential harms and costs?


Likelihood ratios

A Likelihood ratio for a given diagnostic test result compares the likelihood of that result in patients with disease to the likelihood of that result in patients without disease. It provides an estimate of how much a test result will change the odds of disease in a patient.

Please enter data into the 2 by 2 table to determine the likelihood ratio


Dis
Pos
Dis
Neg
Test Pos
Test Neg
SEN:
SPE:
Neg LR:
Pos LR:



How much do LRs change disease likelihood?

LRs greater than 10 or less than 0.1 cause large changes
LRs 5 - 10 or 0.1 - 0.2 cause moderate changes
LRs 2 - 5 or 0.2 - 0.5 cause small changes
LRs less than 2 or greater than 0.5 cause tiny changes
LRs = 1.0 cause no change at all

Key Properties of LRs:

Pretest Probabilities are estimated from published studies of prevalence, data from your practice setting, and your clinical intuition.

How much do LRs change disease likelihood?

LRs greater than 10 or less than 0.1 cause large changes
LRs 5 - 10 or 0.1 - 0.2 cause moderate changes
LRs 2 - 5 or 0.2 - 0.5 cause small changes
LRs less than 2 or greater than 0.5 cause tiny changes
LRs = 1.0 cause no change at all

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Finding articles about a diagnostic test

PubMed:

References:


From: Guyatt, G. Users' Guides to the Medical Literature: Essentials of Evidence-based Clinical Practice. AMA Press, 2002 and Straus. Evidence-Based Medicine. How to Practice and Teach EBM. Churchill-Livingstone, 3rd edition, 2005 (pocket cards).

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