An evidence-based practice is a practice that has been rigorously evaluated in experimental evaluations, like randomized controlled trials, and shown to make a positive, statistically significant difference in important outcomes.
The GRM 8-week in-person group program was studied by the College of Public Health, Kent State University, and was found to be evidence-based, showing statistically significant improvements in participants' knowledge, attitudes, and behaviors related to grief. Beliefs were improved but not to a statistically significant degree. Articles were submitted to the American Journal of Health Education, reviewed by them, and published in their journal.
Information about this study can be found on the GRI Specialist Resource Center under the "GRM Evidence-Based Research" tab.