Levels of Evidence of Sackett and Goldsmith for a Clinical Sign or Symptom

Sackett and Goldsmith developed a grading scheme for evaluating the performance of a clinical sign or symptom for diagnosis of a condition.

Parameters:

(1) type of comparison

(2) study population

(3) criterion for comparison

Comparison	Study Population	Criterion	Level of Evidence
independent and blind	large number of consecutive patients suspected of having the target condition	gold standard	1
independent and blind	small number of consecutive patients suspected of having the target condition	gold standard	2
independent and blind	nonconsecutive patients suspected of having the target condition	gold standard	3
nonindependent	sample of patients who obviously have target condition with or without normal individuals	gold standard	4
nonindependent	NA	other than gold standard (uncertain validity)	5

where:

• Not all combinations of the parameters are provided for in the table.

• A gold standard is one with demonstrated validity for identifying the condition.

• The population in level 4 are of known diagnosis (preselected).

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