Physician referrals play a large role in healthcare in the United states, but in the past the healthcare industry has had no way to track referrals in a standardized way. A study by Michael L. Barnett studied 845,243 patient visits from the National Ambulatory Medical Care Survey and National Hospital Ambulatory Medical Care from 1999 to 2009 and found the probability that an ambulatory visit to a physician resulted in a referral to another physician increased from 4.8% to 9.3%, a 94% increase. The absolute number of visits resulting in a physician referral increased 159% nationally during this time, from 41 million to 105 million. There are an estimated 811,552 physicians, 191,168 dentists, 5,008 hospitals, 5,211 imaging centers, 15,622 nursing centers, 209,499 laboratories in the United States and most of which are all exchanging referrals with paper forms resulting in misplaced patient information, unable to track referrals, no proper backup or reporting system.