The World Health Organization's International Classification of Functioning, Disability and Health (ICF) has provided a new foundation for our understanding of health, functioning, and disability. As a content-valid, comprehensive and universally applicable health classification, it serves as a platform to clarify and specify health-related concepts that are frequently used in the medical literature as well-being, health state, health status, quality of life (QoL) and health-related quality of life (HRQoL). The ICF entities health and health-related domains and functioning will be used as starting point to reach the objective of the paper. Health domains refer to domains intrinsic to the person as a physiological and psychological entity. Health-related domains are not part of a person's health but are so closely related that a description of a person's lived experience of health would be incomplete without them. Functioning refers to all health and health-related domains within the ICF. Well-being is made up of health, health-related, and non-health-related domains, such as autonomy and integrity. QoL is the individual's perceptions of how the life is going in health, health-related, and non-health domains. HRQoL is the individual's perceptions of how the life is going in health and health-related domains. "HRQoL is to QoL as functioning is to well-being". The ICF represents a standardized and international basis for the operationalization of health based on its health domains, and is also the basis for the operationalization of functioning based on all health and health-related domains contained therein. The authors argue that functioning is an operationalization of health from a broader perspective that consider the individual person not only as a biological but also as a social entity.

The World Health Organization's International Classification of Functioning, Disability and Health (ICF) has provided a new foundation for our understanding of health, functioning, and disability. It covers most of the health and health-related domains that make up the human experience, and the most environmental factors that influence that experience of functioning and disability. With the exhaustive ICF, patients' functioning -including its components body functions and structures and activities and participation-, becomes a central perspective in medicine. To implement the ICF in medicine and other fields, practical tools (= ICF Core Sets) have been developed. They are selected sets of categories out of the whole classification which serve as minimal standards for the assessment and reporting of functioning and health for clinical studies and clinical encounters (Brief ICF Core Set) or as standards for multiprofessional comprehensive assessment (Comprehensive ICF Core Set). Different from generic and condition-specific health-status measures, the ICF Core Sets include important body functions and structures and contextual factors. The use of the ICF Core Sets provides an important step towards improved communications between healthcare providers and professionals, and will enable patients and their families to understand and communicate with health professionals about their functioning and treatment goals. Specific applications include multi- and interdisciplinary assessment in clinical settings and in legal expert evaluations and use in disease or functioning-management programs. The ICF has also a potential as a conceptual framework to clarify an interrelated universe of health-related concepts which can be elucidated based on the ICF and therefore will be an ideal tool for teaching students in all medical fields and may open doors to multi-professional learning.

The PECVEC demonstrates adequate psychometric properties for evaluating HRQL in healthy subjects.

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