Table 2. Changes in Volume and Case Mix.

	BPCI			Matched controls			Adjusted differential change in case mix, difference in differences (95% CI)a
	Baseline period	Intervention period	Unadjusted difference	Baseline period	Intervention period	Unadjusted difference
No. of SNFs	448	448		1958	1958
No. of beneficiaries	5075	11 762		20 509	43 302
No. of episodes	5556	13 314		22 562	49 443
Quarterly discharges per SNF, mean (SD)	4.1 (5.4)	2.1 (4.4)	−2.0	3.8 (5.8)	1.8 (4.1)	−2.0	0.0 (−0.3 to 0.4)
Patient characteristics, %
Age, y
≤64	6.2	6.2	0.0	6.5	6.0	−0.5	0.5 (−0.5 to 1.4)
65-79	51.1	50.4	−0.7	50.4	49.5	−0.9	0.2 (−1.9 to 2.3)
≥80	42.7	43.4	0.7	43.1	44.5	1.3	−0.7 (−2.7 to 1.4)
Men	28.3	27.6	−0.7	26.8	28.0	1.2	−1.9 (−3.5 to −0.3)
Women	71.7	72.4	0.7	73.2	72.0	−1.2	1.9 (0.3 to 3.5)
Medicaid dual eligible	16.9	16.6	−0.3	17.5	17.3	−0.3	0.0 (−1.8 to 1.8)
Disabled without end-stage kidney disease	16.2	16.8	0.6	15.7	16.4	0.7	−0.1 (−1.5 to 1.4)
Frailb	9.4	10.4	1.0	9.7	10.8	1.1	−0.06 (−1.41 to 1.29)
Dementiac	4.3	4.4	0.0	5.2	4.4	−0.8	0.8 (0.0 to 1.62)
No. of chronic conditionsd	5.0	5.1	0.1	5.0	5.1	0.1	0.00 (−0.12 to 0.12)
Race/ethnicity
White	89.0	88.8	−0.2	90.0	89.6	−0.4	0.2 (−1.3 to 1.6)
Black	7.3	7.2	−0.2	5.8	6.1	0.2	−0.4 (−1.6 to 0.8)
Hispanic	1.0	0.9	0.0	1.4	1.3	−0.1	0.1 (−0.4 to 0.5)
Unknown or othere	2.7	3.2	0.5	2.8	3.1	0.3	0.2 (−0.4 to 0.8)
Level of complexity, %f
DRG without complications or comorbiditiesf	91.7	90.0	−1.7	91.6	89.7	−1.9	0.21 (−0.9 to 1.3)
DRG with major complications or comorbiditiesg	8.3	10.0	1.7	8.4	10.3	1.9	−0.21 (−1.3 to 0.9)

Abbreviations: BPCI, Bundled Payment for Care Improvement; DRG, diagnosis-related group; LEJR, lower extremity joint replacement; SNF, skilled nursing facility.

^aAdjusted estimates show the differential change in the proportion of patient characteristics between treatment and control groups after vs before BPCI implementation. All estimates use standard errors clustered at the SNF level. The differential change estimates can be interpreted as the average within-SNF change attributable to BPCI implementation.

^bFrailty was defined using a previously validated claims-based frailty index from Kim et al.^21,22 Patients in the top 10% of the frailty index over the entire population of SNF admissions were classified as frail.

^cDementia was defined using International Classification of Diseases-Ninth Revision codes described in Goodman et al.²³ Patients with not otherwise-specified dementia diagnoses were included because routine use of nonspecific diagnostic codes is common, such that excluding them would result in omission of many affected individuals.

^dThe presence of 27 conditions was gathered from the Chronic Condition Data Warehouse, which uses claims since 1999 to describe Medicare beneficiaries’ accumulated chronic disease burden. Chronic conditions were defined as any condition present by the end of the calendar year prior to the LEJR episode. Conditions included Alzheimer disease, Alzheimer disease and related disorders or senile dementia, anemia, asthma, atrial fibrillation, benign prostatic hyperplasia, breast cancer, cataract, chronic kidney disease, chronic obstructive pulmonary disease, colorectal cancer, depression, diabetes, endometrial cancer, glaucoma, heart failure, hip or pelvic fracture, hyperlipidemia, hypertension, hypothyroidism, ischemic heart disease, lung cancer, osteoporosis, prostate cancer, acute myocardial infarction, rheumatoid arthritis, and stroke or transient ischemic attack.

^eThe category of Other includes American Indian or Alaska Native, Asian, Native Hawaiian or Pacific Islander, these are the options for self-identified race/ethnicity in the Medicare enrollment file besides White and Black race or Hispanic/Latino. Less than 1% of beneficiaries are coded as unknown race.

^fWithout complications or comorbidities refers to DRG 470 (LEJR without major complications or coexisting conditions).

^gWith major complications or comorbidities refers to DRG 469 (LEJR with major complications or coexisting comorbidities).