Table 1.

Classification of evidence.¹²

Class	Description
I	Evidence derived from well-planned prospective study conducted in broad spectrum of individuals with the suspected condition, using "gold standard" for defining cases, where test has been applied in blinded manner and enables assessment of appropriate diagnostically accurate tests.
II	Evidence derived from well-planned prospective study conducted in limited spectrum of individuals with the suspected condition, or by well-planned retrospective study in broad spectrum of individuals with confirmed condition (using gold standard), compared with broad spectrum of control subjects, where tests have been applied in blinded manner, and enables measurement of  appropriate diagnostically accurate tests.
III	Evidence derived from retrospective study in limited spectrum of individuals with the confirmed condition and control subjects, in which tests have been applied in blinded manner.
IV	Any design methodology in which test has not been applied in blinded mode or is drawn from evidence based exclusively on opinion of a specialist or on a descriptive casuistic (without controls).