Final answer:
The best estimate of the average percentage of people estimated to experience depression in their lifetime is 15-20%, making it a leading cause among all diseases and injuries as a cause of disability.
Step-by-step explanation:
The best estimate of the average percentage of people estimated to experience depression in their lifetime is 15-20%. This makes it a leading cause among all diseases and injuries as a cause of disability. The United States' disease rate of 33.9% is above average when compared to the estimated range. The U.S. obesity rate, though not mentioned in the question, is considered unusual compared to the average rate. Depression, obesity, and their impacts on mental and physical health are important topics that should be addressed and understood.