Table 2. Comparison of Outcomes in Hospitals in Voluntary MSAs Randomized to Participation, Stratified by Hospital Preperiod Episode Spending^a.

Variable	Spending relative to the regional average for LEJR episodes, No.b
	Quartile 1 (spending lower than regional average)	Quartile 2	Quartile 3	Quartile 4c (spending higher than regional average)
No. of hospitals
All	161	160	160	160
Hospitals in CJR MSAs	56	66	47	60
Hospitals in control MSAs	105	94	113	100
Spending in preintervention period in CJR and control hospitals
Institutional spending, $	23 132	24 079	27 910	37 368
Difference between hospital and CJR regional institutional spending, $d	−4180	−1211	2514	11 506
Mean predicted LEJR institutional spending based on patient risk, $	25 912	26 023	27 145	28 429
Impact of CJR in year 2, before transition to voluntary program (2016-2017)
Change in institutional spending in CJR hospitals vs control hospitals (95% CI), $e	−414 (−939 to 111)	−440 (−874 to −6)	−685 (−1208 to −163)	−1244 (−2110 to −379)
CJR hospitals with no savings bonus, No. (%)f	13 (23.3)	13 (19.7)	12 (25.5)	24 (40.0)
Fraction of hospitals dropping out in year 3 (2018)
Hospitals in CJR MSAs dropping out in year 3, No. (%)	29 (51.8)	48 (72.7)	36 (76.6)	56 (93.3)

Abbreviations: CJR, care for joint replacement; LEJR, lower-extremity joint replacement; MSA, metropolitan statistical area.

^aThese MSAs were randomized to participation vs control. Participation was mandatory in years 1-2 of program and then voluntary in years 3-4 of program.

^bCJR and control hospitals were ranked by how far (measured in US dollars, $) below or above they were from their regions’ average spending per LEJR episode over the period 2012-2014. Regions were defined by the Census division (9 regions) of the hospital’s MSA. After ranks were determined, hospitals were divided evenly into quartiles within the 86 voluntary MSAs. eMethods 2 in the Supplement has details on the model used to rank hospitals.

^cP values reported in the text are from χ² tests of quartiles 1 and 4.

^dRegional institutional spending is the average spending per LEJR episode in the hospital’s region. The difference is the hospital’s average less their regions’ average.

^eEstimates were obtained by running difference-in-differences models similar to the main analysis (described in eMethods 2 in the Supplement) in each quartile separately, comparing year 2 to the preperiod years 2014-2015.

^fIn performance year 2, if hospitals met minimum quality thresholds, then they were eligible to earn a bonus equal to their savings differential (their actual less their target price, capped at 10% of the target price) multiplied by their total LEJR volume in performance period.