Purpose: This paper seeks to contribute to thoughtful description, recording and measurement of functioning, by discussing some fundamental questions to consider before starting, framed as: why, what, how and who.
Method: Generic literature on measurement methods and the more specialised literature on application of the ICF over the last decade inform the consideration of these questions. The context of recording or measurement is examined, including the moral and legal framework of the UN Convention on the Rights of Persons with Disabilities (UNCRPD) and the technical framework of the International Classification of Functioning, Disability and Health (ICF).
Results: Whatever the setting in which describing, recording or measuring is being undertaken - in policy development, service planning and management, clinical management or population health monitoring - determining the purpose is the key starting point. Purpose (why) frames the consideration of content (what), method (how) and source (who). Many generic measurement methods can be applied in the disability field, but there are challenges particular to the field. The perspectives of people with disabilities and "patients" require consideration, especially with the trend to person-centred care and the social justice principles emanating from the UNCRPD.
Conclusions: Considering these basic questions is a pre-requisite to meaningful recording and measurement of functioning and disability. Future challenges include: incorporating environmental factors into measurement; setting thresholds on the disability spectrum; and combining the views of the person concerned with those of various professionals.