"Nearly half of all Americans live with at least one chronic condition, and care for these patients is complex, often involving a number of clinical, occupational, and social services. One study found that the typical primary care doctor has the potential to interact with as many as 229 other doctors, in 117 different practices. Another recent study found that the probability that a physician visit would result in a referral to another physician increased from 4.8 percent in 1999 to 9.3 percent in 2009, a 94 percent increase. The absolute number of ambulatory care visits that resulted in a referral more than doubled in this 10-year period."