"How do you control for the depressive effect of living for extended periods in a hypobaric chamber?"
That's precisely what control groups are for. The idea behind using a hypobaric chamber is that you control for 100% of everything, and only vary the oxygen levels - you could trivially simulate 2500 feet, 5000 feet, 7500 feet and 10,000 feet for a test group, while keeping the control groups at sea level - and observe the differences.
The problem with testing people at "different altitudes" - is there are so many other events that could be contributing (sunlight, exercise, diet, etc...) - hard to eliminate confounding factors.
That's precisely what control groups are for. The idea behind using a hypobaric chamber is that you control for 100% of everything, and only vary the oxygen levels - you could trivially simulate 2500 feet, 5000 feet, 7500 feet and 10,000 feet for a test group, while keeping the control groups at sea level - and observe the differences.
The problem with testing people at "different altitudes" - is there are so many other events that could be contributing (sunlight, exercise, diet, etc...) - hard to eliminate confounding factors.