A study-quality rating meaning evidence from case series, not controlled comparisons.
In the commonly used 5-level evidence hierarchies (e.g., Centre for Evidence-Based Medicine-derived scales widely used in orthopaedics and sports medicine journals), Level IV denotes case series without a comparison group — weaker than randomised trials (Level I) or cohort/case-control studies (Levels II-III), but above expert opinion (Level V). The exact definition varies somewhat by which hierarchy a journal or appraisal tool uses, so it's worth checking the specific grading scheme cited before treating 'Level IV' as a precise, universal category.
This guide was auto-drafted and is pending editorial review.