Determinants of specialist physician ambulatory visits: a neurology example

Figures & data

Table 1. Summary statistics by disease.

	DEM	EPI	MS	PD
Neurologist	19%	51%	59%	57%
Neuro/square mile	0.21	0.22	0.21	0.21
	(1.28)	(1.38)	(1.36)	(1.36)
Neurologist/1,000 capita	0.04	0.04	0.04	0.04
	(0.04)	(0.04)	(0.04)	(0.04)
Union	24%	11%	10%	20%
Female	62%	56%	76%	42%
Age	79.43	45.93	48.37	71.04
	(12.59)	(17.12)	(12.37)	(12.58)
Charlson	1.47	0.60	0.44	0.88
	(1.45)	(1.11)	(0.91)	(1.24)
Medicare	87%	13%	8%	67%
White	75%	74%	75%	76%
African-America	13%	13%	13%	12%
Hispanic	10%	11%	10%	11%
HS or more	86%	86%	86%	86%
Median Income ($10,000)	5.38	5.45	5.58	5.44
Married	50%	50%	50%	50%

Table 2. Summary statistics by physician group

Variables	No Neuro	Neuro	Neither	PCP only	N-only	Both
Neurologist	0%	100%	0%	0%	100%	100%
Neurologist/square mile	0.19	0.23	0.18	0.19	0.29	0.22
	(1.19)	(1.46)	(1.13)	(1.22)	(1.69)	(1.41)
Neurologist/1,000 capita	0.04	0.04	0.04	0.04	0.05	0.04
	(0.04)	(0.04)	(0.04)	(0.04)	(0.04)	(0.04)
Union	20%	14%	11%	24%	10%	15%
Female	59%	59%	58%	60%	56%	59%
Age	67.19	55.55	60.18	70.11	47.74	57.18
	(20.17)	(19.00)	(21.05)	(19.04)	(17.83)	(18.83)
Charlson	1.08	0.83	0.77	1.21	0.35	0.92
	(1.36)	(1.28)	(1.19)	(1.41)	(0.83)	(1.33)
Medicare	57%	32%	41%	64%	16%	35%
White	76%	74%	76%	75%	73%	74%
African-American	13%	13%	12%	13%	13%	13%
Hispanic	10%	11%	10%	11%	12%	11%
HS or more	86%	86%	86%	86%	86%	86%
Median Income ($10,000)	5.33	5.54	5.44	5.27	5.58	5.53
Married	50%	50%	50%	50%	50%	50%
Dementia (DEM)	54%	19%	37%	61%	9%	19%
Epilepsy (EPI)	27%	43%	37%	24%	52%	41%
Multiple Sclerosis (MS)	12%	24%	17%	8%	28%	23%
Parkinson's disease (PD)	7%	13%	8%	6%	11%	14%
Observations	470,438	341,185	143,211	327,227	66,494	274,691

Mean (SD), except where noted. “No Neuro” is a combination of Neither and PCP only. Neuro is a combination of “N-only” and “Both”.

Table 3. Descriptive statistics for 3-digit ZIP codes.

Variable	5th Percentile	Median	95th Percentile	Mean	SD
Land Area (square miles)	41	1,727	9,806	2,931	5,562
Population	68,992	253,093	1,193,455	391,724	389,259
Neurologists	<10	<10	65	17	28
Neurologists/square mile	<0.01	<0.01	23	0.17	1.38
Neurologists/1,000 capita	<0.01	0.03	0.63	0.04	0.04
Observations (# of 3-digit ZIPs)	756
Total Neurologists (2011)	12,391

Table 4. Logistic model results for neurologist/square mile.

Variables	DEM	EPI	MS	PD
	Neurologist	Neurologist	Neurologist	Neurologist
Neurologist/square mile	1.004	1.031***	1.037***	1.036***
	[0.008]	[0.008]	[0.008]	[0.010]
Union	0.907***	1.090***	1.143***	0.817***
	[0.033]	[0.034]	[0.043]	[0.038]
Female	0.860***	1.119***	1.074***	0.916***
	[0.008]	[0.009]	[0.014]	[0.014]
Age	1.187***	1.004***	1.056***	1.183***
	[0.005]	[0.002]	[0.003]	[0.006]
Age^2	0.999***	1.000***	0.999***	0.999***
	[0.000]	[0.000]	[0.000]	[0.000]
Charlson	1.078***	1.011	1.016	0.950***
	[0.009]	[0.007]	[0.012]	[0.012]
Charlson^2	0.998	0.998	0.998	1.005*
	[0.001]	[0.001]	[0.003]	[0.003]
Medicare	1.219***	1.198***	0.954	1.149***
	[0.042]	[0.034]	[0.035]	[0.051]
Percentage white	0.999	1.001	1.000	1.001
	[0.003]	[0.004]	[0.005]	[0.004]
Percentage African-American	1.005	1.005	1.004	1.006
	[0.004]	[0.004]	[0.005]	[0.005]
Percentage Hispanic	1.007**	1.008***	1.009***	1.006***
	[0.003]	[0.001]	[0.002]	[0.002]
Percentage HS or more	0.986**	1.010**	1.009	0.993
	[0.006]	[0.005]	[0.007]	[0.006]
Median income ($10,000)	1.152***	1.077***	1.037	1.134***
	[0.028]	[0.024]	[0.030]	[0.030]
Percentage married	1.002	1.002	1.006	0.999
	[0.006]	[0.005]	[0.007]	[0.007]
Observations	376,579	321,388	157,383	89,221

Notes: Odds ratio [SE]; SE clustered on patient 3-digit ZIP in brackets; year and region dummies included in all models.

***p < 0.01,

**p < 0.05,

*p < 0.1.

Table 5. Logistic model results for neurologist/1,000 capita.

Variables	DEM	EPI	MS	PD
	Neurologist	Neurologist	Neurologist	Neurologist
Neurologist/1,000 capita	2.356*	1.834	2.674	3.897*
	[1.179]	[0.940]	[1.896]	[3.107]
Union	0.908***	1.089***	1.142***	0.817***
	[0.033]	[0.034]	[0.043]	[0.038]
Female	0.860***	1.119***	1.074***	0.916***
	[0.008]	[0.009]	[0.014]	[0.014]
Age	1.187***	1.005***	1.056***	1.183***
	[0.005]	[0.002]	[0.003]	[0.006]
Age^2	0.999***	1.000***	0.999***	0.999***
	[0.000]	[0.000]	[0.000]	[0.000]
Charlson	1.079***	1.011	1.016	0.951***
	[0.009]	[0.007]	[0.012]	[0.012]
Charlson^2	0.998	0.998	0.999	1.004*
	[0.001]	[0.001]	[0.003]	[0.003]
Medicare	1.219***	1.201***	0.953	1.151***
	[0.042]	[0.034]	[0.035]	[0.051]
Percentage white	0.998	1.001	0.999	1.000
	[0.003]	[0.004]	[0.005]	[0.004]
Percentage African-American	1.005	1.004	1.003	1.005
	[0.004]	[0.004]	[0.005]	[0.005]
Percentage Hispanic	1.007**	1.008***	1.008***	1.005**
	[0.003]	[0.001]	[0.002]	[0.002]
Percentage HS or more	0.985**	1.008*	1.007	0.990
	[0.006]	[0.005]	[0.006]	[0.006]
Median income ($10,000)	1.140***	1.077***	1.034	1.123***
	[0.030]	[0.026]	[0.032]	[0.033]
Percentage married	1.007	1.002	1.007	1.002
	[0.006]	[0.006]	[0.008]	[0.008]
Observations	376,472	321,192	157,284	89,180

Notes: Odds ratio [SE]; SE clustered on patient 3-digit ZIP in brackets; year and region dummies included in all models.

***p < 0.01,

**p < 0.05,

*p < 0.1.

Table 6. Multinomial logistic model results for neurologist/square mile.

	Dementia			Epilepsy
Variables	PCP only	N-only	Both	PCP only	N-only	Both
Neurologist/square mile	1.060**	1.080***	1.050*	1.063***	1.072***	1.067***
	[0.028]	[0.028]	[0.030]	[0.017]	[0.017]	[0.018]
Union	1.937***	1.639***	1.547***	2.548***	1.774***	2.131***
	[0.142]	[0.160]	[0.124]	[0.141]	[0.105]	[0.136]
Female	1.102***	0.835***	0.938***	1.046***	0.895***	1.232***
	[0.018]	[0.024]	[0.015]	[0.011]	[0.013]	[0.014]
Age	0.998	1.186***	1.185***	1.004*	1.014***	1.007***
	[0.003]	[0.011]	[0.006]	[0.002]	[0.003]	[0.002]
Age^2	1.000***	0.998***	0.999***	1.000***	1.000***	1.000
	[0.000]	[0.000]	[0.000]	[0.000]	[0.000]	[0.000]
Charlson	1.377***	0.825***	1.463***	1.196***	0.661***	1.258***
	[0.021]	[0.024]	[0.024]	[0.015]	[0.012]	[0.014]
Charlson^2	0.969***	1.006	0.969***	0.982***	1.039***	0.975***
	[0.002]	[0.005]	[0.002]	[0.002]	[0.003]	[0.002]
Medicare	1.302***	1.307***	1.508***	1.109*	1.334***	1.283***
	[0.089]	[0.102]	[0.115]	[0.067]	[0.086]	[0.083]
Percentage white	1.005	0.990	1.005	1.002	0.997	1.005
	[0.008]	[0.007]	[0.009]	[0.007]	[0.006]	[0.008]
Percentage African-American	1.009	1.007	1.014	1.009	1.005	1.012
	[0.012]	[0.011]	[0.013]	[0.007]	[0.006]	[0.008]
Percentage Hispanic	1.018***	1.016***	1.023***	1.019***	1.023***	1.020***
	[0.006]	[0.005]	[0.005]	[0.004]	[0.003]	[0.004]
Percentage HS or more	0.999	0.982	0.986	1.021**	1.026***	1.023**
	[0.012]	[0.012]	[0.011]	[0.010]	[0.008]	[0.010]
Median income ($10,000)	1.018	1.192***	1.164**	0.962	1.068*	1.044
	[0.058]	[0.061]	[0.069]	[0.041]	[0.039]	[0.048]
Percentage married	1.012	1.011	1.013	1.017*	1.006	1.015
	[0.013]	[0.012]	[0.014]	[0.010]	[0.009]	[0.011]
Observations	376,579	376,579	376,579	321,388	321,388	321,388

Table

	Multiple sclerosis			Parkinson’s disease
Neurologist/square mile	1.057***	1.077***	1.064***	1.101***	1.109***	1.106***
	[0.015]	[0.015]	[0.016]	[0.031]	[0.030]	[0.033]
Union	2.521***	1.919***	2.050***	2.992***	1.675***	1.797***
	[0.156]	[0.137]	[0.140]	[0.237]	[0.176]	[0.156]
Female	1.026	0.910***	1.145***	1.183***	0.840***	1.050**
	[0.019]	[0.020]	[0.020]	[0.028]	[0.028]	[0.024]
Age	0.978***	1.049***	1.040***	0.931***	1.126***	1.130***
	[0.004]	[0.006]	[0.005]	[0.006]	[0.011]	[0.008]
Age^2	1.000***	0.999***	1.000***	1.001***	0.999***	0.999***
	[0.000]	[0.000]	[0.000]	[0.000]	[0.000]	[0.000]
Charlson	1.270***	0.658***	1.307***	1.248***	0.638***	1.178***
	[0.025]	[0.018]	[0.023]	[0.028]	[0.022]	[0.026]
Charlson^2	0.975***	1.053***	0.969***	0.982***	1.040***	0.985***
	[0.005]	[0.006]	[0.004]	[0.004]	[0.007]	[0.004]
Medicare	1.066	0.953	1.011	1.245***	0.972	1.329***
	[0.073]	[0.069]	[0.071]	[0.095]	[0.079]	[0.109]
Percentage white	1.006	0.995	1.006	1.004	0.992	1.007
	[0.007]	[0.006]	[0.008]	[0.009]	[0.007]	[0.009]
Percentage African-American	1.016**	1.004	1.015*	1.018*	1.014	1.020*
	[0.008]	[0.007]	[0.009]	[0.011]	[0.009]	[0.012]
Percentage Hispanic	1.017***	1.021***	1.018***	1.021***	1.015***	1.022***
	[0.004]	[0.003]	[0.005]	[0.006]	[0.005]	[0.006]
Percentage HS or more	1.013	1.016*	1.018	1.000	0.990	0.995
	[0.010]	[0.010]	[0.012]	[0.013]	[0.012]	[0.014]
Median income ($10,000)	1.005	1.059	1.030	0.984	1.167***	1.110*
	[0.045]	[0.046]	[0.053]	[0.058]	[0.060]	[0.068]
Percentage married	1.015	1.011	1.015	1.031**	1.019	1.019
	[0.010]	[0.010]	[0.011]	[0.013]	[0.013]	[0.014]
Observations	157,383	157,383	157,383	89,221	89,221	89,221

Notes: Relative Risk [SE]; SE clustered on patient 3-digit ZIP in brackets; year and region dummies included in all models. Omitted group—not seeing any physician.

***p < 0.01,

**p < 0.05,

*p < 0.1.

Table 7. Multinomial logistic model results for neurologist/1,000 capita.

	Dementia			Epilepsy
Variables	PCP only	N-only	Both	PCP only	N-only	Both
Neurologist/1,000 capita	3.633	8.390	6.659	0.862	2.000	1.722
	[6.426]	[13.372]	[11.493]	[0.869]	[1.869]	[1.760]
Union	1.939***	1.641***	1.551***	2.543***	1.769***	2.127***
	[0.142]	[0.161]	[0.124]	[0.141]	[0.105]	[0.136]
Female	1.102***	0.834***	0.938***	1.046***	0.895***	1.232***
	[0.018]	[0.024]	[0.015]	[0.011]	[0.013]	[0.014]
Age	0.998	1.186***	1.185***	1.004*	1.014***	1.007***
	[0.003]	[0.011]	[0.006]	[0.002]	[0.003]	[0.002]
Age^2	1.000***	0.998***	0.999***	1.000***	1.000***	1.000
	[0.000]	[0.000]	[0.000]	[0.000]	[0.000]	[0.000]
Charlson	1.377***	0.825***	1.464***	1.195***	0.661***	1.257***
	[0.021]	[0.024]	[0.024]	[0.015]	[0.012]	[0.014]
Charlson^2	0.969***	1.006	0.969***	0.982***	1.039***	0.975***
	[0.002]	[0.005]	[0.002]	[0.002]	[0.004]	[0.002]
Medicare	1.302***	1.310***	1.508***	1.113*	1.340***	1.289***
	[0.089]	[0.102]	[0.115]	[0.067]	[0.087]	[0.083]
Percentage white	1.004	0.989*	1.004	1.002	0.996	1.004
	[0.008]	[0.007]	[0.009]	[0.007]	[0.006]	[0.008]
Percentage African-American	1.008	1.004	1.013	1.006	1.002	1.009
	[0.012]	[0.010]	[0.012]	[0.007]	[0.006]	[0.008]
Percentage Hispanic	1.018***	1.015***	1.023***	1.018***	1.023***	1.019***
	[0.006]	[0.005]	[0.005]	[0.004]	[0.003]	[0.004]
Percentage HS or more	0.996	0.978*	0.983	1.020**	1.024***	1.021**
	[0.012]	[0.012]	[0.011]	[0.009]	[0.008]	[0.010]
Median income ($10,000)	1.014	1.181***	1.147**	0.978	1.077*	1.053
	[0.063]	[0.067]	[0.076]	[0.044]	[0.043]	[0.052]
Percentage married	1.013	1.013	1.018	1.008	1.000	1.009
	[0.015]	[0.014]	[0.016]	[0.011]	[0.011]	[0.012]
Observations	376,472	376,472	376,472	321,192	321,192	321,192

Table

	Multiple sclerosis			Parkinson's disease
Neurologist/1,000 capita	0.912	2.969	2.519	1.061	1.671	5.111
	[1.090]	[3.320]	[3.103]	[1.870]	[2.849]	[9.158]
Union	2.518***	1.917***	2.048***	2.987***	1.671***	1.796***
	[0.156]	[0.137]	[0.140]	[0.237]	[0.176]	[0.155]
Female	1.025	0.910***	1.144***	1.183***	0.840***	1.051**
	[0.019]	[0.020]	[0.020]	[0.028]	[0.028]	[0.024]
Age	0.978***	1.049***	1.040***	0.930***	1.126***	1.130***
	[0.004]	[0.006]	[0.005]	[0.006]	[0.011]	[0.008]
Age^2	1.000***	0.999***	1.000***	1.001***	0.999***	0.999***
	[0.000]	[0.000]	[0.000]	[0.000]	[0.000]	[0.000]
Charlson	1.269***	0.658***	1.306***	1.249***	0.639***	1.180***
	[0.025]	[0.018]	[0.023]	[0.028]	[0.022]	[0.026]
Charlson^2	0.975***	1.053***	0.970***	0.982***	1.039***	0.985***
	[0.005]	[0.006]	[0.004]	[0.004]	[0.007]	[0.004]
Medicare	1.067	0.953	1.012	1.249***	0.975	1.334***
	[0.073]	[0.069]	[0.071]	[0.095]	[0.079]	[0.109]
Percentage white	1.005	0.993	1.005	1.003	0.991	1.005
	[0.007]	[0.006]	[0.008]	[0.009]	[0.007]	[0.009]
Percentage African-American	1.012	1.001	1.012	1.014	1.009	1.016
	[0.008]	[0.007]	[0.009]	[0.011]	[0.009]	[0.012]
Percentage Hispanic	1.016***	1.020***	1.018***	1.020***	1.014***	1.021***
	[0.004]	[0.004]	[0.005]	[0.006]	[0.005]	[0.006]
Percentage HS or more	1.012	1.013	1.016	0.998	0.987	0.991
	[0.010]	[0.010]	[0.012]	[0.013]	[0.012]	[0.013]
Median income ($10,000)	1.018	1.064	1.034	1.002	1.186***	1.110
	[0.049]	[0.051]	[0.057]	[0.066]	[0.069]	[0.076]
Percentage married	1.008	1.007	1.013	1.020	1.009	1.017
	[0.011]	[0.012]	[0.013]	[0.016]	[0.015]	[0.017]
Observations	157,284	157,284	157,284	152,407	152,407	152,407

Notes: Relative Risk [SE]; SE clustered on patient 3-digit ZIP in brackets; year and region dummies included in all models. Omitted group—not seeing any physician.

***p < 0.01,

**p < 0.05,

*p < 0.1.