The International Classification of Functioning, Disability and Health (ICF) classifies disability in three interrelated areas, as follows:
- Impairment: loss or abnormality of a body part (i.e., structure) or body function (i.e., physiological function including mental functions),
- Activity limitation: difficulties an individual may have in executing activities, and
- Participation restriction: problems an individual may experience in life situations.
Disability refers to challenges faced in all three areas. Disability denotes the negative aspects of the interaction between an individual’s health condition and that individual’s environmental or personal factors (WHO 2013).
Disability is best understood as a continuum. In terms of difficulty functioning, the ‘difficulty’ can be operationalized through a range of descriptors from no difficulty at all, to some difficulty, to a lot of difficulty, to completely unable to carry out the action. Each of these descriptors represents a possible cut-off, or threshold, in the determination of a final disability identifier; for example, to define those with and without disability.
Depending on purpose, disability prevalence is not a single statistic. It can be calculated at various thresholds to serve purpose for both data collection and reporting. For example, if the purpose is to provide for equitable access to public spaces, then the level of inclusion for a disability identifier might be some difficulty, since those with even minor levels of difficulty functioning would likely benefit from adaptations made to remove barriers and ease access. Alternatively, if the purpose is to provide subsidies or allowances, the level of inclusion for a disability identifier might be cannot do at all since only those with more severe functional limitations would meet stricter eligibility criteria.
Disability statistics can highlight disparities, such as if there are employment gaps between people with disability and people without disability.