Degree of Scientific Evidence Classification Scheme
The classification scheme defines 5 separate evaluation categories for prevention interventions. The scheme classifies interventions according to degree of scientific rigor and strength of evidence of effectiveness. Evidence is strengthened by solid evaluation methods and positive outcomes. Evidence is weakened by flaws in evaluation methods and either no positive outcomes or negative outcomes. Additionally, interventions may show anecdotal effectiveness, but have not yet been scientifically evaluated. Learn more about why evaluation is important.
Meets CDC-designated "Best-Evidence" * |
Meets CDC-designated "Promising Evidence" * |
Shows Promise |
Potentially Effective |
Research Ongoing |
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| Study Design | Randomized Controlled Trial (RCT)** | Single group pre-post test or Non-randomized control group | Randomized Controlled Trial (RCT)** | Process evaluation only
Formative findings Sound methodology Based on scientific theory Appropriate for population |
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| Sample Size | 50+ subjects per arm at all data points |
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Less than 50 subjects per group at any data point | ||
| Follow-up | 3-month or more follow-up | 1-month or more follow-up | Less than 1 month follow-up | ||
| Retention Rate | 70% or more retention rate | 60% or more retention rate | Less than 60% retention rate | ||
| Outcome Measures | Positive and statistically significant intervention effect for 1+ outcome measure
No negative and statistically significant intervention effect |
Positive and statistically significant intervention effect for 1 or more outcome measure
No negative and statistically significant intervention effect |
Positive and statistically significant intervention effect for 1 or more outcome measure | May have no significant positive intervention effects | |
| Statistical Variance | No statistical differences in baseline levels of the outcome or differences were controlled for |
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May have statistical differences in baseline levels of outcome measures | ||
| Analysis | Regardless of the level of intervention exposure
Based on 2-sided test |
May be based on intervention exposure
Based on either 2-sided test or 1-sided test if direction is hypothesized |
Based on either 2-sided test or 1-sided test if direction is hypothesized | May be based on intervention exposure
Based on either 2-sided test or 1-sided test if direction is hypothesized
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| Overall Fatal Flaw | No evidence of fatal flaw | May have fatal flaw | At least one fatal flaw | ||
| * Based on CDC HIV/AIDS Prevention Research Synthesis Project ** Randomized Controlled Trial: test by comparison of two groups - an intervention group and a control group - in which participants are randomly assigned to either group |
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