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Internal Validity (Evidence Rating Element)

The degree to which observed changes can be attributed to the program. The validity of a study depends on both the research design and the measurement of the program activities and outcomes. Threats to internal validity may affect the extent to which observed effects may be attributed to a program or intervention, on’s Scoring Instrument, which includes: Attrition, Maturation, Instrumentation, Regression toward the Mean, Selection Bias, Contamination, and History, as well as other factors. See Program Review and Rating from Start to Finish for more information.

On’s Scoring Instrument for practices, internal validity is measured by the number of randomized controlled trials used to calculate the mean effect size. Mean effect sizes calculated using only randomized controlled trials are considered to have fewer threats to internal validity then mean effect sizes calculated using only quasi-experimental designs. See Practice Review and Rating from Start to Finish for more information.