Challenges to change: competition.
D000293:Adolescent; D000328:Adult; D003695:Delivery of Health Care / Q000639:trends*; D004465:Economic Competition / Q000639:trends*; D004467:Economics / Q000639:trends*; D006279:Health Maintenance Organizations / Q000639:trends; D006801:Humans; D013333:Student Health Services / Q000639:trends*; D014481:United States