During July 1965-June 1967 an estimated 94.9 million persons, or 49.5 percent of the civilian, noninstitutional population, had one or more chronic conditions. About 22.0 million persons re-ported that they were limited to some extent in their activities as a result of their chronic diseases or impairments, and 6.3 million experienced limitation of mobility to some degree. Persons with limitation of activity had an average of 3.4 chronic conditions, of which 1.4 conditions were reported as causes of limitation. Persons with limitation of mobility had an average of 4.1 chronic conditions, of which 1.5 were named as causes of limitation. Two condition groups, heart conditions and arthritis and rheumatism, were the primary causes of both activity and mobility limitations during July 1965-June 1967; heart conditions were reported as causing 16.4 percent of the activity limitations and 12.6 percent of the mobility limitations, and arthritis and rheumatism caused 14.8 percent of the activity limitations and 24.4 percent of the mobility limitations. These two condition groups were the leading causes of activity limitation in each of four time periods for which reports on causes of limitation of activity have been published from the information derived from the Health Interview Survey. Two condition groups have shown substantial changes in level as causes of activity limitation. Impairments (except paralysis) of back or spine increased from alow of 6.6 percent of limitations during July 1959-June 1961 to 8.2 percent of limitations during July 1965-June 1967. The second group, hypertension without heart involvement, declined as a leading cause from 6.8 percent in July 1959-June 1961 to 5.4 percent during July 1965-June 1967.
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