Which of the following factors contributes most to rising U.S. healthcare costs?

The aging population and the prevalence of chronic diseases significantly contribute to the rising healthcare costs in the U.S. As people age, they often experience a higher incidence of chronic conditions such as diabetes, heart disease, and arthritis, which require ongoing and sometimes intensive medical management. This increased demand for healthcare services leads to higher spending on treatments, medications, and long-term care.

Furthermore, an aging population typically means that there are more individuals who require healthcare services more frequently, thereby elevating overall costs associated with hospitalizations, outpatient visits, and specialized care. The combination of an older demographic and the rise in chronic diseases creates a substantial burden on the healthcare system, driving up costs as providers cater to these complex and ongoing health needs.

Other factors mentioned, such as increased out-of-pocket payments from patients, may influence individual patients' perceptions of costs but do not fundamentally drive the overall increase in healthcare expenditures like the aging population and the prevalence of chronic diseases do. Similarly, a reduction in new medical technologies would likely lead to lower costs rather than higher ones, and a decreased demand for healthcare services would suggest a decrease in costs rather than an increase.