Qualifiers are measures recorded after the relevant domain, to indicate the extent of 'problem' with an aspect of functioning. A uniform or 'generic' qualifier scale is provided to record the extent of the 'problem' in relation to impairment, activity limitation and participation restriction. It is recognised that the generic qualifier requires calibration to relate its scale to existing measurement tools. The Environmental factors qualifier uses both a positive and negative scale, to indicate the extent to which an environmental factor acts as either a facilitator or barrier to a person's functioning.

Two constructs, 'performance' and 'capacity', are also used with the generic qualifier scale for the Activities and Participation domains. These constructs provide one way of indicating the environment in which measurement has taken place and how it can be changed to enhance functioning. 'Capacity' relates to what an individual can do in a 'standardised' environment (this often involves some kind of clinical assessment) while 'performance' relates to what the person actually does in their 'current' (usual) environment.

'The gap between capacity and performance reflects the difference between the impacts of current and uniform environments, and thus provides a useful guide as to what can be done to the environment of the individual to improve performance' (WHO 2001:15).

Measurement using ICF is an area for further development.