Causes parallel the evolutionary changes occurring in the US medical system: payment based on quantity of services delivered, not quality; aging of the population increases the prevalence and complexity of chronic health conditions, most of which are handled in primary care settings; and increasing emphasis on life-style changes and preventative measures, often poorly covered by health insurance or not at all.[19] In 2004, the median income of specialists in the US was twice that of PCPs, and the gap is widening.[20] Discontent by practicing primary care internists is discouraging trainees from entering primary care; in a 2007 survey of 1,177 graduating US medical students, only 2% planned to enter a general internal medicine career, and lifestyle was emphasized over the higher subspecialty pay in their decision.[21] Primary care practices in the United States increasingly depend on foreign medical graduates to fill depleted ranks.[19]