We operate in one line of business, which is operating hospitals and related health care entities. We operate in two geographically organized groups: the National and American Groups. The National Group includes 95 hospitals located in Alaska, California, Florida, southern Georgia, Idaho, Indiana, northern Kentucky, Nevada, New Hampshire, North Carolina, South Carolina, Utah and Virginia, and the American Group includes 83 hospitals located in Colorado, northern Georgia, Kansas, southern Kentucky, Louisiana, Mississippi, Missouri, Tennessee and Texas. We also operate six hospitals in England, and these facilities are included in the Corporate and other group.

Adjusted segment EBITDA is defined as income before depreciation and amortization, interest expense, gains on sales of facilities, losses on retirement of debt, income taxes and net income attributable to noncontrolling interests. We use adjusted segment EBITDA as an analytical indicator for purposes of allocating resources to geographic areas and assessing their performance. Adjusted segment EBITDA is commonly used as an analytical indicator within the health care industry, and also serves as a measure of leverage capacity and debt service ability. Adjusted segment EBITDA should not be considered as a measure of financial performance under generally accepted accounting principles, and the items excluded from adjusted segment EBITDA are significant components in understanding and assessing financial performance. Because adjusted segment EBITDA is not a measurement determined in accordance with generally accepted accounting principles and is thus susceptible to varying calculations, adjusted segment EBITDA, as presented, may not be comparable to other similarly titled measures of other companies. The geographic distributions of our revenues, equity in earnings of affiliates, adjusted segment EBITDA and depreciation and amortization for the quarters and nine months ended September 30, 2019 and 2018 are summarized in the following table (dollars in millions):


	Quarter						Nine Months
	2019			2018			2019			2018
Revenues:
National Group	$	6,398		$	5,542		$	19,159		$	16,719
American Group		5,780			5,396			17,001			16,113
Corporate and other		516			513			1,653			1,571

	$	12,694		$	11,451		$	37,813		$	34,403

Equity in earnings of affiliates:
National Group	$	2		$	(1	)	$	(3	)	$	(5	)
American Group		(10	)		(10	)		(32	)		(29	)
Corporate and other		4			2			12			9

	$	(4	)	$	(9	)	$	(23	)	$	(25	)

Adjusted segment EBITDA:
National Group	$	1,270		$	1,127		$	4,088		$	3,593
American Group		1,185			1,072			3,443			3,250
Corporate and other		(170	)		(103	)		(412	)		(402	)

	$	2,285		$	2,096		$	7,119		$	6,441

Depreciation and amortization:
National Group	$	291		$	245		$	839		$	702
American Group		277			258			828			765
Corporate and other		79			79			235			230

	$	647		$	582		$	1,902		$	1,697


Adjusted segment EBITDA	$	2,285		$	2,096		$	7,119		$	6,441
Depreciation and amortization		647			582			1,902			1,697
Interest expense		448			442			1,386			1,309
Gains on sales of facilities		—			(6	)		(17	)		(420	)
Losses on retirement of debt		211			9			211			9

Income before income taxes	$	979		$	1,069		$	3,637		$	3,846