Table 2. Regression Analysis of Study Samplea.
| Variables | IRR (95% CI) |
|---|---|
| Patient characteristics (N = 3 446 338) | |
| Insured | |
| Privately, always | 1 [Reference] |
| Medicare, ever | 1.81 (1.79-1.83)b |
| Medicaid, ever | 1.94 (1.93-1.95)b |
| Uninsured, ever | 1.61 (1.60-1.62)b |
| Poverty in patient’s zip code | |
| Low | 1 [Reference] |
| Medium | 1.11 (1.10-1.12)b |
| High | 1.17 (1.16-1.17)b |
| Visit characteristics | |
| Infrequent user (0-3 visits) in prior y | 1 [Reference] |
| Frequent user in prior y | |
| 4-10 visits | 1.64 (1.62-1.66)b |
| 11-17 visits | 1.97 (1.86-2.08)b |
| ≥18 visits | 5.91 (5.00-6.98)b |
| Primary MH diagnosis | 1.31 (1.30-1.32)b |
| Admitted inpatient | 4.88 (4.83-4.93)b |
| Diagnoses | |
| Mental illness | 1.26 (1.22-1.29)b |
| MH diagnosis (Healthcare Cost and Utilization Project) | |
| Mild | 1.03 (1.02-1.04)b |
| Moderate | 1.12 (1.11-1.13)b |
| Severe | 1.23 (1.22-1.24)b |
| Residual codes (omitted) | |
| Infectious and parasitic diseases | 1.00 (1.0-1.01) |
| Neoplasms | 1.04 (1.03-1.05)b |
| Endocrine, nutritional, and metabolic diseases and immunity disorders | 0.99 (0.99-1.0)c |
| Diseases of the blood and blood-forming organs | 0.83 (0.82-0.84)b |
| Diseases of the nervous system and sense organs | 1.22 (1.21-1.22)b |
| Diseases of the circulatory system | 1.06 (1.05-1.06)b |
| Diseases of the respiratory system | 1.22 (1.21-1.23)b |
| Diseases of the digestive system | 1.13 (1.12-1.14)b |
| Diseases of the genitourinary system | 1.19 (1.18-1.19)b |
| Complications of pregnancy, childbirth, and the puerperium | 1.04 (1.03-1.05)b |
| Diseases of the skin and subcutaneous tissue | 1.33 (1.32-1.34)b |
| Diseases of the musculoskeletal system and connective tissue | 1.25 (1.24-1.25)b |
| Congenital anomalies | 0.98 (0.95-1.00)d |
| Certain conditions originating in the perinatal period | 0.98 (0.82-1.18) |
| Injury and poisoning | 0.98 (0.98-0.99)b |
| Symptoms, signs, and ill-defined conditions | 1.17 (1.16-1.17)b |
| Interactions | |
| MH × Medicare insured, ever | 0.84 (0.83-0.85)b |
| MH × Medicaid insured, ever | 0.87 (0.87-0.88)b |
| MH × uninsured, ever | 0.93 (0.92-0.94)b |
| MH × medium poverty in patient's zip code | 0.97 (0.96-0.98)b |
| MH × high poverty in patient's zip code | 0.96 (0.94-0.97)b |
| MH × frequent user (4-10 visits) in prior y | 0.68 (0.67-0.69)b |
| MH × frequent user (11-17 visits) in prior y | 0.62 (0.59-0.66)b |
| MH × frequent user (≥18 visits) in prior y | 0.54 (0.45-0.64)b |
| MH × admitted inpatient | 0.68 (0.67-0.69)b |
| MH × infectious and parasitic diseases | 1.01 (1.00-1.03)c |
| MH × neoplasms | 0.93 (0.91-0.94)b |
| MH × endocrine, nutritional, and metabolic diseases and immunity disorders | 0.93 (0.92-0.94)b |
| MH × diseases of the blood and blood-forming organs | 1.00 (0.99-1.02) |
| MH × diseases of the nervous system and sense organs | 1.04 (1.03-1.05)b |
| MH × diseases of the circulatory system | 0.99 (0.98-1.00)b |
| MH × diseases of the respiratory system | 0.97 (0.96-0.98)b |
| MH × diseases of the digestive system | 1.03 (1.02-1.03)b |
| MH × diseases of the genitourinary system | 0.94 (0.93-0.95)b |
| MH × complications of pregnancy, childbirth, and the puerperium | 1.06 (1.04-1.08)b |
| MH × diseases of the skin and subcutaneous tissue | 0.88 (0.87-0.89)b |
| MH × diseases of the musculoskeletal system and connective tissue | 1.00 (0.99-1.01) |
| MH × congenital anomalies | 1.03 (0.99-1.07) |
| MH × certain conditions originating in the perinatal period | 0.93 (0.73-1.19) |
| MH × injury and poisoning | 1.15 (1.14-1.16)b |
| MH × symptoms, signs, and ill-defined conditions | 1.12 (1.11-1.13)b |
Abbreviations: IRR, incidence rate ratio; MH, mental health.
a
Negative binomial regression analysis (log link function) with an outcome variable indicating the total count of emergency department visits in the 365 days following the index visit. Diagnoses are grouped according to the Healthcare Cost and Utilization Project’s Clinical Classification Software and represent any diagnosis recorded in any visit to the emergency department or inpatient hospitalization following an emergency department visit. The omitted diagnosis group is residual codes, unclassified, and E codes (Clinical Classification Software category 18).
b
P < .01.
c
P < .05.
d
P < .10.