Exhibit 1.

Characteristics of the study population, by type of procedure and the vertical integration status of physician group practices, 2013–16

	Independent physicians		Integrated physicians
Characteristics	Mean/number	SD	Mean/number	SD
IMAGING TESTS
Hospital-based share (%)	67.9	36.8	76.9	25.9
Medicare spending amounta ($)	291.0	158.6	307.4	154.4
Number of observationsb	8,472,312	—c	547,329	—c
Number of patients	10,273,507	—c	3,055,382	—c
Number of procedures	23,203,571	—c	6,294,305	—c
LABORATORY TESTS
Hospital-based share (%)	53.6	39.6	61.2	35.1
Medicare spending amounta ($)	14.0	6.5	16.1	9.4
Number of observationsb	16,957,889	—c	655,996	—c
Number of patients	11,392,161	—c	5,473,899	—c
Number of procedures	283,544,892	—c	57,820,793	—c

SOURCE Authors’ analysis of Medicare fee-for-service claims data, 2013–16. NOTES “Integrated physicians” are those whose practices have been acquired by a hospital or health system. SD is standard deviation.

^aPer procedure.

^bNumber of observations at the year-month-procedurephysician group level.

^cNot applicable.