| Quality |
Designation Criteria |
| |
U. S. Preventive Services Task Force (1989) |
| Level I |
Evidence from one well-conducted randomized clinical trial |
| Level II-1 |
Evidence from one well-conducted study with controls but without randomization |
| Level II-2 |
Evidence from one well-designed cohort or case-control study preferably from independent researchers |
| Level II-3 |
Evidence from multiple time-series single-subject investigations or dramatic results from non-controlled experiments |
| Level III |
Opinions of authorities, descriptive studies, case studies, reports of expert committees |
| |
Section 1 Task Force of the Division of Clinical Psychology of the American Psychological Association Task Force (1998) |
| Demonstrated Effectiveness |
Two or more well-conducted group-design studies conducted by different research teams showing the treatment to be better than an alternative treatment or equivalent to an already established treatment or a large series of well-conducted single-subject design studies with n > 9 that compare the intervention to another treatment |
| Probable Efficacy |
Two or more well-conducted group- and/or single-subject design studies (n < 3) showing the treatment superior to a no-treatment, baseline, or alternative treatment condition or two well-conducted group-design studies meeting criteria for demonstrated effectiveness but both studies conducted by the same research team |
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