NOTE: Estimates of board-certified physicians are based on the number of valid certificates issued, and may not accurately reflect the number of currently practicing physicians in the United States. Also, because provider types may be credentialed as well as licensed or hold more than one credential, the numbers in each category are not mutually exclusive.

SOURCE: Numbers of board-certified physicians come from the

^aAmerican Board of Internal Medicine (ABIM, 2006a);

^cAmerican Board of Family Medicine (ABFM, 2006c);

^eAmerican Board of Pediatrics (ABP, 2006b); and

^gAmerican Board of Psychiatry and Neurology, Inc. (ABPN, 2006b).

Professional organization membership comes from the

^bAmerican College of Physicians (ACP, 2006);

^dAmerican Academy of Family Physicians (AAFP, 2006);

^fAmerican Academy of Pediatrics (AAP, 2006);

^hPersonal communication, Lisa Corchado, American Psychiatric Association, September 4, 2007;

ⁱAmerican Society of Clinical Oncology (ASCO, 2006); and

^jAmerican Society of Pediatric Hematology/Oncology (ASPHO, 2006).