any tool, scale, questionnaire, or procedure used to measure an outcome domain in clinical research or practice. Instruments can be:
Quantitative: e.g., blood pressure, laboratory values, physical performance tests.
Qualitative: e.g., quality-of-life measures, patient satisfaction, or other subjective experiences.
They may be disease-specific (tailored to a particular condition) or generic (applicable across multiple conditions). Organizations like OMERACT evaluate instruments to ensure they measure the intended domain accurately, detect meaningful differences, and are feasible to use.
Abbreviation: OMI
Synonyms: Outcome Instrument, Outcome Measure, Clinical Outcome Assessment (COA) (FDA term, Instrument, Tool
Example
Health Assessment Questionnaire–Disability Index (HAQ-DI) to measure physical function in rheumatology.
MRI Scoring Systems to quantify inflammation in specific joints.
(Both are OMIs used to assess key domains of health outcomes.)