floor effect
Statistical phenomenon where assessment scores cluster at the lowest possible value, limiting ability to measure improvement.
Full Definition
A floor effect occurs when a significant proportion of study participants achieve the lowest possible score on an assessment instrument, creating a distribution skewed toward the minimum value. This statistical artifact limits the instrument's ability to detect improvement or differentiate between participants at the lower end of the scale. In psychiatric research, floor effects can compromise study outcomes when patients have mild symptoms at baseline or when assessment instruments lack sensitivity for detecting subtle changes. Floor effects are particularly problematic in clinical trials of maintenance treatments or relapse prevention studies where participants may have minimal symptoms at study entry.
Usage
Usage note: Hyphenate when used as compound modifier: 'floor-effect phenomenon'.
In Context
- "The depression scale showed a floor effect with 35% of participants scoring zero at baseline." — Psychometric analysis report
- "Floor effects in the anxiety measure limited our ability to demonstrate further symptom reduction." — Clinical trial manuscript