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Insurance Impact on Nonurgent and Primary Care-Sensitive Emergency Department Use
Weiwei Chen, PhD; Teresa M. Waters, PhD; and Cyril F. Chang, PhD
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Insurance Impact on Nonurgent and Primary Care-Sensitive Emergency Department Use

Weiwei Chen, PhD; Teresa M. Waters, PhD; and Cyril F. Chang, PhD
The authors analyzed the association of insurance coverage and likelihood of an ED visit being nonurgent or primary care—sensitive based on an ED classification algorithm.
Objectives: To analyze the relationship between insurance and the likelihood of a nonurgent or primary care–sensitive (PCS) emergency department (ED) visit. Study Design: Retrospective cohort study.

Methods: The probabilities of nonurgent and PCS ED visits were derived on the basis of the New York University ED Classification Algorithm. We constructed a logit quasi-likelihood model to examine the insurance impact using 2008 Tennessee Hospital Outpatient Discharge Data.

Results: Among a total of 2,177,955 ED visits in the analysis, uninsured status was significantly associated with the likelihood that an ED visit was nonurgent or PCS. These associations were different for men and women and across major racial groups. On average, uninsured status was associated with an increased probability of 0.038 of being nonurgent and 0.054 of being PCS, relative to private insurance status. The corresponding numbers for public insurance status were 0.060 and 0.075, respectively. For nonurgent or PCS probabilities that are not close to 0, higher nonurgent or PCS likelihoods corresponded to lower ED cost per visit to third-party insurers and patients.

Conclusions: Lack of insurance was associated with a higher probability of a nonurgent or PCS ED visit when compared with private insurance. When uninsured individuals gain coverage under the Affordable Care Act through either Medicaid expansion (public coverage) or insurance exchanges (private coverage), the average nonurgent or PCS probabilities could change either way given the opposite effects of public and private insurance coverage. If a lower nonurgent or PCS likelihood materialized, it could be associated with higher ED costs.

Am J Manag Care. 2015;21(3):210-217
  • Lack of insurance was associated with a higher probability of both types of emergency department (ED) visits compared with private insurance.
  • Our model can be used by health policy makers in other states to gain insights into potential changes in ED use under the Affordable Care Act.
Lack of insurance coverage and the resulting difficulties in accessing basic health services have often been cited as major contributing factors in driving uninsured patients to seek care at hospital emergency departments (EDs).1-3 However, recent studies have shown that most of the growth in ED volume has been driven by insured patients, with Medicaid-insured individuals being more likely than other patients to have multiple ED visits.4,5 Insured persons (with and without a usual source of medical care) have been found equally likely to have 1 or more ED visits in a 12-month period compared with their uninsured counterparts.4,6 In terms of ED misuse, many studies have documented significant nonurgent ED visits by both insured and uninsured patients.7-9

This paper seeks to investigate the relationship between insurance coverage and the likelihood of an ED visit being nonurgent or primary care–sensitive (PCS), using the New York University (NYU) ED Algorithm, a retrospective ED classification system developed by NYU. This computerized classification system has been used to document and track the prevalence and variations of potentially avoidable ED use and has the additional advantage of incorporating empirically verified definitions of nonurgent and PCS ED visits.10

We constructed a statistical model to examine the effects of insurance type using ED visit records from the 2008 Tennessee Hospital Outpatient Discharge Data Set. We also discussed how a change in insurance mix under national healthcare reform might impact the average likelihood of nonurgent or PCS ED visits and associated ED expenses.

Our paper contributes to the literature in 2 significant ways. First, we modeled the actual ED visit probabilities from the NYU ED Algorithm, whereas most previous studies have used dichotomized nonurgent visits as the dependent variable, ignoring potentially interesting variation in underlying probabilities. Second, while our study was limited to a single state (Tennessee), it provides a timely model that can be used by policy makers in other states to gain insights into potential changes in ED use under the Affordable Care Act (ACA).

Data Source and Study Variables

Our main data source was the 2008 Tennessee Hospital Discharge Data Set (HDDS). ED visits were identified from outpatient discharge records and included all ED visits from licensed nonfederal, short-term Tennessee hospitals, regardless of whether the visit resulted in hospitalizations later. We also used the Tennessee Joint Annual Report of Hospitals and the Area Resource File to provide information on hospital and county characteristics.

Our 2 key study variables, the probabilities of nonurgent and PCS ED visits, were based on the NYU ED Algorithm, which was designed to use limited information found in discharge abstracts (primarily diagnosis codes) to classify ED visits. We applied this algorithm to the 2,807,874 ED visits found in the 2008 Tennessee HDDS file to create 9 probabilities that added up to 1 (or 100%) for each ED record. The 9 NYU ED probability categories are: “ne” (non-emergent), “epct” (emergent/primary care treatable), “edcnpa” (emergent/ED care needed/preventable and avoidable), “edcnnpa” (emergent/ED care needed and not preventable/avoidable), “injury” (injury principal diagnoses), “psych” (mental health principal diagnoses), “alcohol” (alcohol-related health principal diagnoses), “drug” (drug-related health principal diagnoses, excluding alcohol), or “unclassified” (not in one of the above categories). The relationship among the categories is depicted in the Figure.

The values of the first 4 NYU ED categories were continuous, ranging from 0 to 1, while the other 5 categories were binary, with values of 1 or 0. When an ED visit fell into any of the last 5 ED categories (eg, injury, psych), the value of each of the other 8 categories was 0. The intuition of the NYU ED classification was that for each ED encounter with a valid diagnostic code, the probabilities created represent “the relative percentage of cases for that diagnosis falling into the various classification categories.”11 For example, in the case of urinary tract infections (International Classification of Diseases, Ninth Revision, Clinical Modification [ICD-9-CM] code 599.0), each case was designated as “non-emergent” (66%), “emergent/primary care treatable” (17%), and “emergent/ED care needed/ preventable and avoidable” (17%).11 We excluded visits made by non-Tennessee residents (6.6% of the total visits) and observations with missing or unknown values in explanatory variables (15.8% of the total visits). Our final data set contained 2,177,955 ED visits. The distribution of insurance types among the 15.8% of the sample excluded was similar to that of the remaining sample, so excluding these observations introduced little bias.

We used 2 dependent variables in our regressions: likelihood of a nonurgent ED visit and likelihood of a PCS ED visit. We regrouped and combined the first 2 NYU ED categories (“ne” and “epct”) into 1 probability and labeled it “nonurgent” (Figure). These ED visits were made by patients with conditions that could have been adequately treated in a primary care setting and did not need to be seen in a hospital ED; common examples of nonurgent ED visits included sore throat and minor back problems.

Our second dependent variable, the probability of a PCS ED visit, was created by combining the probability of a nonurgent ED case (first dependent variable) with the probability of the third NYU ED category (“edcnpa”), representing the probability of a needed but potentially preventable and avoidable ED visit. These ED visits have been referred to as “primary care–sensitive” ED visits in the literature because they are potentially modifiable by, and therefore sensitive to, the effective delivery of primary care outside the hospital.12 This term is similar to the term “ambulatory care–sensitive” condition in that both terms emphasize good outpatient care delivered in a timely manner. However, the term “ambulatory care–sensitive” is often used in the context of inpatient hospitalizations, while “primary care–sensitive” is used in the context of ED visits. The latter term also focuses on primary care, a subset of all ambulatory care, as being an important utilization driver. Our use of the term “primary care–sensitive” is consistent with the NYU ED category definitions.

Our primary independent (predictor) variable—insurance type—and other covariates were drawn from 3 major conceptual domains: patient-visit characteristics, hospital characteristics, and the external access-to-care environment. Insurance types from the 2008 Tennessee HDDS included private insurance, Medicaid and Medicare, uninsured, and other insurance (eg, TRICARE and workers’ compensation). Other patient-visit characteristic variables from the 2008 Tennessee HDDS include patient age, gender, race, and ethnicity, Charlson Comorbidity Index (CCI) (calculated from the patient’s ICD-9-CM codes and related procedure codes), whether the ED visit was a repeated visit in 2008, and total number of ED visits per patient in 2008.

Hospital characteristics included ownership (public, nonprofit, or for-profit) and medical school affiliation. External access-to-care variables included the following county-level measures: primary care physicians (PCP) per 1000 persons, percent of population 65 years and older, percent of population below the federal poverty line, whether the county was designated a partial or full Health Professional Shortage Area, whether the county was part of a Metropolitan Statistical Area, and whether the county was in the eastern, central, or western section of Tennessee.

To explore the potentially heterogeneous impact of insurance across gender and racial/ethnic groups, we included interaction terms among insurance types, gender, and race.


Because our dependent variables were continuous but bounded—taking on any value between 0 and 1, including 0 and 1—standard linear regression models were not appropriate because a) the resulting predicted values could not be guaranteed to lie between 0 and 1; and b) their variance would not be constant (a violation of the standard regression models).13,14 Previous studies have dealt with these problems by dichotomizing the outcome; for example, defining a visit to be nonurgent or PCS if the relevant probability was above a predetermined cutoff. However, this approach loses the substantial, potentially interesting information captured in the relative probability levels. Therefore, we used the actual probabilities generated by the NYU ED Algorithm, and modeled them using an econometric method developed for fractional or proportional dependent variables by Papke and Wooldridge.13

We modeled our outcomes using a logit quasi-likelihood model. Independent variables included patient visit characteristics, hospital characteristics, neighborhood characteristics, and interaction terms among insurance types, race, and gender to explore the potentially heterogeneous impact of these variables. Quasi-likelihood estimation was performed in STATA 12 (College Station, Texas), with error terms clustered at the patient level. Adjustment for patient-level clustering was necessary because we observed a large number of repeated ED visits.

To illustrate the policy relevance of our regression results, we also produced evidence on how nonurgent and PCS probabilities were associated with costs of ED services to third-party insurers and patients. ED costs were estimated by applying hospital-specific revenue-to-charge ratios to billed ED charges. We then arrayed nonurgent and PCS probabilities of patients in the sample from low to high based on their quintiles, and examined the pattern of average ED costs corresponding to the probabilities in each quintile.


Descriptive statistics for our final sample are presented in Table 1. In 2008, ED visits in Tennessee had average probabilities of being nonurgent and PCS of 0.515 and 0.587, respectively. For comparison, we also included statewide population averages for certain key variables (last column). It is important to keep in mind that our primary data represented visits, while our comparison data were population-based. To the extent that visits represented unique individuals, however, this comparison provides some insight regarding differences between the population seeking care at EDs and the overall Tennessee population.

Among the 2,177,955 ED visits in our analysis, public insurance (Medicaid and Medicare) was the largest payer for Tennessee residents (52%); this percentage was significantly higher than the proportion of Tennesseans enrolled in these public programs in 2008 (31%). In contrast, 17% of ED visits were made by uninsured patients, while only 15% of Tennesseans were uninsured in 2008.

Table 2 presents results from our 2 predictive equations (probabilities of an ED visit being nonurgent and PCS, respectively). Chi-square statistics for both equations (P <.001) suggest overall significance of the models.

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