PVD is a primary cause of impairment in persons over the age of 60, as well as in diabetics. Up to 40% of persons with PVD show no symptoms. However, severe cases may include pain, stiffness, and deformity when walking or standing. According to the National Institute of Disability and Rehabilitation Research (NIDRR), people with disabilities are individuals who have limitations due to damage, disease, or illness that prevent them from performing activities such as hearing, vision, speech, cognitive, or physical abilities. These limitations can be permanent or temporary and can affect anyone's ability to function independently. People with disabilities make up 18% of the U.S. population. They are more likely than others to live in poverty, to use institutional care instead of personal assistance services, and to experience other barriers to independence. Disability is not just about physical impairments. It can also mean having an emotional or mental disorder. This would include disorders such as anxiety, depression, bipolar disorder, and schizophrenia. There are many ways in which these conditions can limit an individual's ability to function independently. For example, someone who has panic attacks when confronted with social situations might suffer from a disabling condition. Disability isn't limited to physical problems either.