Chronic diseases, residual injuries, permanent damage or defects from birth can impair how well a person functions day to day. How people experience and cope with a disability can be greatly affected by the opportunities and services provided for them. Human function can be measured by alterations to body structure or function (impairment), activity limitations and restrictions in participation. Severe or profound core activity limitation can be measured by calculating the percentage of people who ‘sometimes’ or ‘always’ need help with core activities of daily living (mobility, self-care or communication). The likelihood of having a severe or profound core activity limitation generally increases with age.