The model of disablement suggested by the World Health Organization (WHO) has provided useful conceptual distinctions for impairment, disability, and handicap. In practical terms, impairment occurs at the organ level, representing any loss or abnormality of psychological, physiological, or anatomical structure or function. Disability occurs at the time the persons level, demonstrated as any restriction or lack of ability (resulting from an impairment) to perform any activity in the manner or within the range considered normal for a human being. Handicap occurs at the societal level. It is a disadvantage for a given individual, resulting from an impairment or a disability, that limits or prevents the fulfillment of a role that is normal (depending on age, sex, and social and cultural factors) for that individual.