Examples of scales used for guidelines: Evolution of grades of decisions on preventive services.
| EVIDENCE | CTFPHC FROM 1989 | CTFPHC FROM 1997 AND USPSTF FROM 2007 | CTFPHC FROM 2009: GRADE |
|---|---|---|---|
| Positive | A: Good evidence to support inclusion in a PHE | A: High certainty that net benefit is substantial | Positive: strong Desirable effects of the intervention outweigh its undesirable effects. Implies that most individuals will be best served by this action |
| B: Fair evidence to support inclusion in a PHE | B: High certainty that the net benefit is moderate or moderate certainty that the net benefit is moderate to substantial | Positive: weak Desirable effects probably outweigh the undesirable effects but uncertainty exists | |
| Middle | C: Poor evidence to support inclusion or exclusion, but recommendations might be made on other grounds | C: At least moderate certainty that net benefit is small | NA |
| Negative | D: Fair evidence to exclude from consideration in a PHE | D: Moderate or high certainty that service has no net benefit or that harms outweigh benefits | Weakly against Undesirable effects probably outweigh the desirable effects, but uncertainty exists. When the balance between desirable and undesirable effects is small, the quality of evidence is lower, and there is more variability in the values and preferences of individuals |
| E: Good evidence to exclude from a PHE | Strongly against Confident that the undesirable effects of intervention outweigh its desirable effects | ||
| Insufficient | NA | I: Current evidence is insufficient to assess the balance of benefits and harms. Evidence is lacking, of poor quality, or conflicting, and the balance of benefits and harms cannot be determined | NA |
CTFPHC—Canadian Task Force on Preventive Health Care; GRADE—Grading of Recommendations Assessment, Development and Evaluation; NA—not applicable; PHE—periodic health examination; USPSTF—United States Preventive Services Task Force.