Level I:

Randomized Controlled Trials (RCT); experimental studies; or systematic reviews of RCTs with or without meta-analysis

Level II:

Quasi-experimental studies; systematic reviews of a combination of RCTs and quasi-experimental studies or quasi-experimental studies only, with or without meta-analysis

Level III:

Non-experimental studies; qualitative studies; systematic review of a combination of RCTs, quasi-experimental and non-experimental studies or non-experimental studies, only with or without meta-analysis; systematic review of qualitative studies, with or without meta-synthesis

Level IV:

Opinion of respected authorities and/or reports of nationally recognized expert committees based on scientific evidence

Level V:

Evidence obtained from literature reviews, quality improvement documents, program evaluation, financial evaluations, case studies, or opinions of nationally recognized experts based on experimental evidence