Table 2. The modified Royal College of General Practitioners 3-star system for evidence assessment.

Evidence level	Definition
★★★	Strong evidence: provided by generally consistent findings in multiple, high quality, scientific studies, based on at least 2 independent studies.
★★	Moderate evidence: provided by generally consistent findings in fewer, smaller or lower quality, scientific studies, based on at least 2 studies.
★	Limited evidence: provided by one scientific study or inconsistent findings in multiple scientific studies.
-	No scientific evidence: no conclusions can be drawn when there are not any studies that meet the criteria.