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Spoont M, Arbisi P, Fu S, et al. Screening for Post-Traumatic Stress Disorder (PTSD) in Primary Care: A Systematic Review [Internet]. Washington (DC): Department of Veterans Affairs (US); 2013 Jan.

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Screening for Post-Traumatic Stress Disorder (PTSD) in Primary Care: A Systematic Review [Internet].

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APPENDIX CLEVELS OF EVIDENCE

Based on Criteria for the Rational Clinical Examination Series (Simel 2008)7

Level I Evidence

Independent, blind comparison of sign or symptom results with a “gold standard” of anatomy, physiology, diagnosis, or prognosis among a large number of consecutive patients suspected of having the target condition.

  • Independent: neither the test result nor the gold standard result are used to select patients for the study.
  • Blind: test and gold standard each applied and interpreted without knowledge of the result of the other.
  • Gold Standard: the results of biopsy, angiography, autopsy, xray, sonogram, physiologic study, follow-up, therapeutic response, etc. that establish the true anatomy, physiology, diagnosis or outcome of the target condition.
  • Target Condition: the anatomic or physiologic state, disease, syndrome, prognosis or therapeutic response that the sign or symptom is designed to identify.
  • Large Numbers: sufficient numbers of patients to have narrow confidence limits on the resulting sensitivity, specificity, or likelihood ratio.

Level II Evidence

Independent, blind comparison of sign or symptom results with a “gold standard” among a small number of consecutive patients suspected of having the target condition.

  • Small Number: insufficient numbers of patients to have narrow confidence limits on the resulting sensitivity, specificity, or likelihood ratio. (N.B. You should note that the definition of “small” is relative and depends on the size of all extant studies. For example, if you have several studies of many hundreds of patients, then a study of only 80 patients might be considered small.)

Level III Evidence

Independent, blind comparison of signs and symptoms with a “gold standard” among non-consecutive patients suspected of having the target condition. The short-coming here is restricting the study sample to a subset of patients who both underwent and generated definitive results on both the sign or symptom and the application of the gold standard. The results over-estimate accuracy.

Level IV Evidence

Non-independent comparison of signs and symptoms with a “gold standard” among “grab” samples of patients who obviously have the target condition plus, perhaps, normal individuals. In addition to the selection bias of Level III, these studies restrict their samples to the obvious, “black or white” presentations (sometimes even selected on the basis of their gold standard result) that don't need a clinical examination (other than pattern recognition), and exclude the “shades of gray” that comprise the clinical spectrum of early as well as late, mild as well as severe, and other but commonly confused conditions. The results greatly over-estimate accuracy.

Level V Evidence

Non-independent comparisons of signs and symptoms with a standard of uncertain validity (which may even “incorporate” the sign or symptom result in its definition) among “grab” samples of patients plus, perhaps, normals. In addition to the biases of Level IV, these studies often include the sign or symptom result as part of a “lead standard,” resulting in a self-fulfilling prophesy. The results extravagantly over-estimate accuracy.

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