From: The ethics of clinical innovation in psychopharmacology: Challenging traditional bioethics
Level I: Double-blind randomized trials | Ia: Placebo-controlled |
 | Ib: Non placebo-controlled |
Level II: Open randomized trials | Â |
Level III: Naturalistic studies | IIIa: Nonrandomized, controlled studies |
 | IIIb: Large nonrandomized, uncontrolled studies (n > 100) |
 | IIIc: Medium-sized nonrandomized, uncontrolled studies (100 > n > 50) |
Level IV: Small naturalistic studies (nonrandomized, uncontrolled, (50 > n > 10) | |
Level V: Case series (n < 10), Case report (n = 1), Expert opinion | |
Adapted by us from principles of Evidence-based Medicine [9] | |
In terms of the timeline of how the discovery process proceeds, this schema is inverted. Everything begins at level V with novel observations and clinical innovation, and proceeds upwards. Putting emphasis on the utility of controlled studies should not lead to the conclusion that research simply consists of doing controlled studies. |