Final answer:
Physicians' decisions have a significant impact on healthcare expenditures in the U.S., due in part to the fee-for-service model which increases healthcare costs without clear health benefits.
Step-by-step explanation:
The question relates to the percentage of healthcare expenditures influenced by physician's decisions. In the United States, a substantial portion of healthcare spending is tied to these decisions, especially considering the fee-for-service model. Under this system, physicians are incentivized to provide more services, such as additional tests or scans, which may not always be necessary. This can lead to higher healthcare costs and increased spending without a corresponding improvement in health outcomes, which are often more dependent on factors like diet, exercise, and genetics rather than healthcare expenditure.