TABLE 3.

Regression covariate estimates for the difference-in-difference regression model.

Parameter	Estimate	Std Error	95% Confidence Interval	p value
Illinois (reference: Missouri)	0.00926	0.00698	−0.00448, 0.02300	0.186
Hlinois*2011	Ref
Illinois*2012	−0.00105	0.00274	−0.00645, 0.00435	0.702
Illinois*2013	−0.00250	0.00337	−0.00914, 0.00413	0.458
Illinois*2014	0.00163	0.00452	−0.00727, 0.01053	0.719
Illinois*2015	0.00895	0.00529	−0.00147, 0.01938	0.092
Illinois*2016	0.01405	0.00555	0.00312, 0.02499	0.012
Area Deprivation Index	0.00065	0.00013	0.00038, 0.00091	0.000
Number of orthopedic surgeons	0.00004	0.00002	0.00000, 0.00008	0.041
Female (reference: male)	0.00977	0.00119	0.00742, 0.01212	0.000
Age	−0.00306	0.00031	−0.00366, −0.00246	0.000
Herfindahl-Hirschman Index	0.02011	0.01167	−0.00294, 0.04315	0.087
Pairwise comparisons of interaction terms	Contrast sum of squares	Std Error	T value	p value
niinois*2012 vs Illinois*2013	0.00146	0.00240	0.61	0.544
Illinois*2014 vs Illinois*2013	0.00413	0.00316	1.31	0.192
Illinois*2015 vs Illinois*2013	0.01146	0.00377	3.04	0.003
Illinois*2016 vs Illinois*2013	0.01656	0.00393	4.21	<0.001

Individual years (without state interaction) and model intercept were also included in the regression model, but are not shown here. State*year interaction terms demonstrate a statistically significant downward associations in Medicaid-funded orthopaedic surgeries prior to the date of Medicaid expansion in Illinois (January 1,2014) and significant upward associations in the post-expansion years. Pairwise comparisons of the state*year interaction variable in post-expansion years vs 2013 are included at the bottom of the table.