The Friction Model - a dynamic model of functioning, disability and contextual factors and its conceptual and practical applicability.

Purpose. To develop a model of the dynamics of functioning, disability and contextual factors which harmonises with the International Classification of Functioning, Disability and Health (ICF). Method. Model parts based on ICF were identified and a model drawing from engineering concepts was developed. The conceptual and practical applicability of the model was discussed. Results. The so called Friction Model was created, which incorporates the ICF entities capacity, performance, environmental factors, health condition, body functions and structures, and personal factors. Friction describes the interaction between a person and his or her environment. The coefficient of friction is defined as the ratio between capacity and performance. Conclusion. Carrying conceptual strengths and limitations, the Friction Model appears to offer opportunities for practical applications, including ICF-based alternatives to health-economic analyses. Harmonising with the ICF model and terminology, the model uses friction to describe the interaction between a person and the environment. The coefficient of friction can be used as a simple measure of how facilitating an environment is. The applicability is not limited to functioning of people with impairments.