Explaining the link between access-to-care factors and health care resource utilization among individuals with COPD

Figures & data

Figure 1 Sample extraction.

Table 1 Descriptive statistics: unweighted/weighted N=9,332/2,091,774

Continuous variables	Mean (standard deviation)
	All samples	Hospital/ED visit			PCP office visit
		Yes	No	Univariate logit test	Yes	No	Univariate logit test
Number of pulmonary care specialists per 100,000 persons	3.06 (3.49)	2.91 (3.44)	3.09 (3.50)	P=0.361	3.06 (3.40)	3.06 (3.56)	P=0.999
Number of RHCs per 100,000 persons	1.91 (4.88)	2.06 (4.84)	1.89 (4.89)	P=0.420	1.86 (4.72)	1.96 (5.01)	P=0.704
Number of FQHCs per 100,000 persons	2.16 (4.12)	2.41 (4.27)	2.11 (4.09)	P=0.069	2.19 (4.05)	2.14 (4.17)	P=0.635
Number of hospitals per 100,000 persons	2.10 (1.82)	2.26 (1.87)	2.07 (1.80)	P=0.024*	NA
Number of PCPs per 10,000 persons	7.06 (3.07)	NA			7.07 (3.03)	7.05 (3.10)	P=0.823
Categorical variables	Proportion (%)
	All samples	Proportion of hospital/ED visit = yes (chi-square test)	Proportion of PCP office visit = yes (chi-square test)
Hospital/ED visit			P<0.001*
Yes	16.2	NA	90.6
No	83.8		35.2
PCP office visit		P<0.001*
Yes	44.2	33.3	NA
No	55.8	2.7
Annual income		P<0.001*	P<0.001*
<$15k	22.6	26.5	51.4
$15k–<$25k	27.6	18.0	45.5
$25k–<$35k	14.0	13.3	43.2
$35k–<$50k	13.7	12.4	38.0
$50k–<$70k	11.3	8.8	42.0
≥$70k	10.9	6.5	37.1
COPD medication		P<0.001*	P<0.001*
0	42.3	7.7	24.8
1	22.4	13.2	43.9
2	16.3	20.8	59.3
3	9.6	30.8	72.4
≥4	9.4	38.8	76.9
Age-group (years)		P=0.015*	P=0.002*
18–34	11.2	16.2	32.8
35–44	10.7	22.6	46.1
45–54	20.8	19.1	49.7
55–64	24.9	14.6	45.8
65+	32.3	13.5	42.7
Sex		P=0.048*	P<0.001*
Male	43.1	14.3	37.9
Female	56.9	17.6	49.0
Race		P<0.001*	P=0.005*
Caucasian	77.6	13.9	42.1
African–American	11.7	28.2	54.2
Hispanic	4.7	18.3	41.4
Other races	5.9	21.7	53.7
Marital status		P=0.021*	P=0.115
Married	48.9	14.1	44.3
Single	14.8	18.6	40.5
Divorced	20.2	20.1	48.1
Widowed	12.9	14.8	43.6
Separated	3.1	18.4	37.2
Education		P<0.001*	P=0.202
Some high school	22.6	22.0	47.9
High-school graduation	34.7	15.8	43.3
Some college	30.7	14.3	42.9
College graduation	12.0	11.4	43.1
Employment		P<0.001*	P=0.003*
Yes	30.7	11.1	39.5
No	69.3	18.5	46.3
Smoking status		P=0.577	P=0.008*
Nonsmoker	59.0	16.6	46.5
Current smoker	41.0	15.7	40.9
Myocardial infarction		P<0.001*	P<0.001*
Yes	16.6	26.7	56.4
No	83.4	14.1	41.8
Angina or coronary heart disease		P<0.001*	P<0.001*
Yes	16.8	24.6	56.3
No	83.2	14.5	41.8
Stroke		P<0.001*	P=0.073
Yes	8.9	23.1	49.1
No	91.1	15.6	43.7
Asthma		P<0.001*	P<0.001*
Yes	42.9	20.8	54.2
No	57.1	12.8	36.7
Cancer		P=0.823	P=0.007*
Yes	21.9	16.5	48.4
No	78.1	16.1	43.0
Arthritis		P=0.233	P<0.001*
Yes	57.1	17.0	48.4
No	42.9	15.2	38.5
Depression		P<0.001*	P<0.001*
Yes	39.2	19.8	50.1
No	60.8	13.9	40.4
Kidney disease		P<0.001*	P=0.003*
Yes	7.0	24.7	54.2
No	93.0	15.6	43.4
Diabetes		P=0.004*	P<0.001*
Yes	20.0	20.2	52.1
No	80.0	15.2	42.2

Notes: Region, health care coverage, and year variables were not included in Table 1.

* P<0.05.

Abbreviations: ED, emergency department; RHCs, rural health centers; FQHCs, federally qualified health centers; NA, not applicable; PCP, primary care physician.

Table 2 Results of bivariate probit model with two outcomes (hospital/ED visit and PCP office visit) (unweighted/weighted N=9,332/2,091,774)

Outcomes	Bivariate probit model (unweighted/weighted N=9,332/2,091,774)
	Hospital/ED visit			PCP office visit
Covariates (reference group)	Coefficient	P-value	Marginal effect	Coefficient	P-value	Marginal effect
Pulmonary care specialists per 100,000 persons	−0.019	0.028*	−0.004	−0.007	0.461	−0.002
RHCs per 100,000 persons	−0.003	0.704	−0.001	−0.002	0.637	−0.001
FQHCs per 100,000 persons	0.007	0.401	0.001	0.003	0.741	0.001
Hospitals per 100,000 persons	0.037	0.032*	0.008	NA
PCPs per 10,000 persons	NA			0.002	0.872	0.001
Annual income ($35k–<$50k)
<$15k	0.266	0.021*	0.060	0.174	0.071	0.058
$15k–<$25k	0.115	0.282	0.024	0.140	0.091	0.046
$25k–<$35k	−0.018	0.869	−0.004	0.116	0.183	0.038
$50k–<$70k	−0.150	0.188	−0.028	0.109	0.233	0.036
≥$70k	−0.390	0.003*	−0.065	−0.067	0.518	−0.022
COPD medication (no medication)
1	0.307	<0.001*	0.051	0.519	<0.001*	0.181
2	0.639	<0.001*	0.128	0.892	<0.001*	0.323
3	0.988	<0.001*	0.232	1.251	<0.001*	0.450
≥4	1.099	<0.001*	0.270	1.362	<0.001*	0.485
Health care coverage	−0.150	0.122	−0.031	0.065	0.462	0.021
Age-group (18–34)
35–44	−0.057	0.699	−0.015	0.076	0.576	0.025
45–54	−0.166	0.180	−0.041	0.139	0.221	0.046
55–64	−0.441	0.001*	−0.099	−0.077	0.490	−0.026
65+	−0.521	<0.001*	−0.114	−0.221	0.072	−0.072
Male	−0.172	0.007*	−0.036	−0.313	<0.001*	−0.104
Race (Caucasian)
African–American	0.393	<0.001*	0.092	0.253	0.009*	0.085
Hispanic	0.123	0.542	0.026	0.038	0.812	0.013
Other races	0.126	0.323	0.027	0.160	0.111	0.054
Marital status (married)
Single	−0.123	0.298	−0.025	−0.127	0.146	−0.042
Divorced	−0.060	0.456	−0.013	−0.125	0.064	−0.041
Widowed	−0.173	0.029*	−0.035	−0.240	<0.001*	−0.079
Separated	−0.200	0.173	−0.040	−0.422	0.003*	−0.136
Education (some high school)
High-school graduation	−0.099	0.222	−0.021	−0.081	0.271	−0.027
Some college	−0.098	0.265	−0.021	−0.089	0.245	−0.030
College graduation	−0.044	0.673	−0.009	0.022	0.809	0.007
Employed	−0.142	0.086	−0.029	0.099	0.145	0.033
Smoker	−0.093	0.136	−0.019	−0.137	0.012*	−0.046
Region (Northeast)
Midwest	−0.113	0.261	−0.025	−0.053	0.520	−0.018
South	−0.212	0.030*	−0.046	−0.140	0.101	−0.046
West	−0.162	0.123	−0.035	0.015	0.870	0.005
Comorbidities
Myocardial infarction	0.302	0.001*	0.063	0.202	0.012*	0.067
Angina or coronary heart disease	0.181	0.020*	0.038	0.208	0.003*	0.069
Stroke	0.032	0.704	0.007	−0.092	0.233	−0.030
Asthma	−0.022	0.718	−0.005	0.048	0.364	0.016
Cancer	0.033	0.617	0.007	0.073	0.184	0.024
Arthritis	−0.099	0.095	−0.021	0.102	0.051	0.034
Depression	0.035	0.567	0.007	0.069	0.229	0.023
Kidney disease	0.168	0.078	0.035	0.087	0.313	0.029
Diabetes	0.025	0.717	0.005	0.054	0.406	0.018
Year (2011)	0.072	0.186	0.015	0.077	0.121	0.026
Constant	−0.850	<0.001*	NA	−0.678	<0.001*	NA

Note:

* P<0.05. Rho (ρ)=0.691 (P<0.001).

Abbreviations: ED, emergency department; RHCs, rural health centers; FQHCs, federally qualified health centers; NA, not applicable; PCP, primary care physician.

Table 3 Results of sensitivity analysis based on lagged values of county-level variables

Outcomes	Hospital/ED visit			PCP office visit
Covariates	Coefficient	P-value	Marginal effect	Coefficient	P-value	Marginal effect
All lagged variables
Pulmonary care specialists per 100,000 persons	−0.019	0.041*	−0.004	−0.005	0.589	−0.002
RHCs per 100,000 persons	−0.003	0.642	−0.001	−0.003	0.529	−0.001
FQHCs per 100,000 persons	0.009	0.311	0.002	0.003	0.701	0.001
Hospitals per 100,000 persons	0.036	0.037*	0.008	NA
PCPs per 10,000 persons	NA			−0.003	0.758	−0.001
Lagged variables of pulmonary specialists and safety net facilities
Pulmonary care specialists per 100,000 persons	−0.019	0.042*	−0.004	−0.008	0.409	−0.003
RHCs per 100,000 persons	−0.003	0.611	−0.001	−0.003	0.554	−0.001
FQHCs per 100,000 persons	0.008	0.314	0.002	0.003	0.705	0.001
Hospitals per 100,000 persons	0.038	0.027*	0.008	NA
PCPs per 10,000 persons	NA			0.002	0.822	0.001
Lagged variables of pulmonary specialists only
Pulmonary care specialists per 100,000 persons	−0.018	0.045*	−0.004	−0.008	0.419	−0.003
RHCs per 100,000 persons	−0.002	0.740	−4.75E–04	−0.002	0.642	−0.001
FQHCs per 100,000 persons	0.007	0.397	0.001	0.003	0.738	0.001
Hospitals per 100,000 persons	0.038	0.031*	0.008	NA
PCPs per 10,000 persons	NA			0.002	0.814	0.001

Note:

* P<0.05.

Abbreviations: ED, emergency department; RHCs, rural health centers; FQHCs, federally qualified health centers; NA, not applicable; PCP, primary care physician.

Table 4 Results of subpopulation analyses based on existence of pulmonary specialists

Outcomes	Hospital/ED visit			PCP office visit
Covariates	Coefficient	P-value	Marginal effect	Coefficient	P-value	Marginal effect
Number of pulmonary specialists =0 (unweighted/weighted N=2,581/512,339)
Pulmonary care specialists per 100,000 persons	NA			NA
RHCs per 100,000 persons	−0.001	0.836	−3.06E–04	−0.005	0.409	−0.002
FQHCs per 100,000 persons	0.013	0.216	0.003	0.005	0.596	0.002
Hospitals per 100,000 persons	0.056	0.005*	0.012	NA
PCPs per 10,000 persons	NA			0.002	0.914	0.001
Number of pulmonary specialists >0, including pulmonary care specialist variable (unweighted/weighted N=6,751/1,579,435)
Pulmonary care specialists per 100,000 persons	−0.028	0.016*	−0.006	−0.007	0.522	−0.002
RHCs per 100,000 persons	−0.010	0.632	−0.002	−0.008	0.633	−0.003
FQHCs per 100,000 persons	0.001	0.888	2.76E–04	−0.005	0.563	−0.002
Hospitals per 100,000 persons	0.026	0.369	0.005	NA
PCPs per 10,000 persons	NA			0.003	0.805	0.001

Note:

* P<0.05.

Abbreviations: ED, emergency department; RHCs, rural health centers; FQHCs, federally qualified health centers; NA, not applicable; PCP, primary care physician.

Table S1 Correlation between outcome variables

	Hospital/ED visit	PCP office visit
Hospital/ED visit	1.00
PCP office visit	0.40 (P<0.001)	1.00

Abbreviations: ED, emergency department; PCP, primary care physician.

Table S2 Results of supplementary analysis based on safety net facilities categorical variable

Outcomes	All samples (unweighted/weighted N=9,332/2,091,774)
	Hospital/ED visit			PCP office visit
Covariates (reference group)	Coefficient	P-value	Marginal effect	Coefficient	P-value	Marginal effect
Pulmonary care specialists per 100,000 persons	−0.020	0.029*	−0.004	−0.006	0.482	−0.002
Safety net facilities (no facility)
RHCs and FQHCs	0.066	0.489	0.014	0.097	0.315	0.032
RHCs only	−0.042	0.726	−0.008	−0.014	0.909	−0.004
FQHCs only	0.030	0.758	0.006	0.031	0.755	0.010
Hospitals per 100,000 persons	0.040	0.016*	0.008	NA
PCPs per 10,000 persons	NA			0.002	0.826	0.001

Note:

* P<0.05.

Abbreviations: ED, emergency department; RHCs, rural health centers; FQHCs, federally qualified health centers; NA, not applicable; PCP, primary care physician.