Data and sample
Data came from the 2001 to 2006 National Hospital Ambulatory Medical Care Survey Emergency Department (NHAMCS-ED) databases, which are developed and made available by the National Center for Health Statistics (NCHS) at the Centers for Disease Control and Prevention. The NHAMCS-ED is a national probability sample of visits to the emergency departments of general and short-stay hospitals, exclusive of federal, military, and Department of Veterans Affairs hospitals, located in the 50 states and the District of Columbia. Data from hospital units of other acute care and long-term care institutions are not included. This study was determined to be exempt from institutional review board review, because the NHAMCS-ED data are deidentified and publicly available.
Data from 2001 and subsequent years were used, because 2001 was the first year that the NHAMCS-ED database included the duration of emergency department visits. The 2001 to 2006 NHAMCS-ED databases contain 218,179 visit records. Records for 467 individuals who died in the emergency department or were dead on arrival were excluded because the duration of these visits was not comparable to others. Of the remaining 217,712 records, 20,762 had no information on visit duration, which left a sample of 196,950. The raw data included some implausibly short visits (less than .02 hours) and some unusually long visits (more than 47 hours). Uncommonly short and long durations threaten robust inference and external validity because they can disproportionately influence estimates of trends in mean values. To reduce the influence of outliers, the lowest and highest 1% of visit durations (3,873 records), which corresponded to visits shorter than 20 minutes and longer than 21 hours, were removed or "trimmed." Consequently, the final sample contained 193,077 visit records, and our results pertain to the 98% trimmed mean for visit durations.
The NHAMCS sample is selected from approximately 1,900 geographically defined primary sampling units (PSUs) that cover the 50 states and the District of Columbia. The 1,900 PSUs are stratified by socioeconomic and demographic variables and then selected with a probability proportional to their size. Stratification is done within four geographical regions by metropolitan statistical area status.
For each emergency department, visits are selected over a randomly assigned four-week reporting period. NCHS staff exclude from the data visits solely for administrative purposes, such as payment of a bill, and visits in which no medical care is provided, such as visits to deliver a specimen. NHAMCS-ED information on visits is extracted by hospital staff from patients' charts and from hospitals' administrative files. A brief, one-page patient record form is completed for each sample visit. Data entries are independently checked by the NCHS for quality control purposes.
Mental health-related visits
Trends in the duration of visits made primarily for mental health reasons were compared with trends in the duration of visits made for other, non-mental health reasons. Reasons for the visit are entered as text by hospital staff members and are later assigned numeric codes by the NCHS. Up to three reasons for the visit can be listed (52% of records listed only one reason); respondents are instructed to list the primary reason first. Reasons were classified as mental health related if they included common symptoms of mental disorders (for example, distress, hopelessness, anxiety, or hostility), problems and symptoms resulting from use of alcohol or drugs, mental health and substance use disorders, need for a mental health or psychological evaluation, suicidal behaviors and intentional self-injuries, and need for counseling for various social problems. All other reasons were classified as non-mental health related. Visits were classified as having been associated with a mental health complaint if the primary reason for the visit corresponded to an issue related to mental health or substance use. Visits related to substance use were included in the mental health category because patients' mental health and substance use complaints frequently co-occur and because mental health assessments are usually required when substance use is the primary reason for the visit.
Covariates
Diagnosis categories. On the basis of ICD-9 codes listed in the visit record, visits were assigned to one of four diagnosis categories by use of a hierarchy (highest to lowest order): serious mental illness, substance use disorders, other mental disorders, and no mental disorder diagnosis. Up to five diagnoses are listed on a visit record. The visit was assigned to the highest-order category among the diagnoses listed. The serious mental illness category included schizophrenia spectrum disorders ( ICD-9 295.x), bipolar disorders (296.0, 296.1, and 296.4–296.9), major depression with psychotic features (296.24 and 296.34), and other psychotic disorders (297.x and 298.x). The substance use disorder category included abuse and dependence disorders for alcohol and illicit substances (303.x–305.x, except 305.1). All other mental disorder diagnoses (290.x–319.x, excluding the serious mental illness and substance use disorder diagnoses) were grouped together. All other diagnoses were grouped under no mental disorder diagnosis.
Discharge status. NHAMCS-ED discharge status codes (for example, inpatient admission, transfer, and leaving the emergency department without being seen) are revised annually. Before 2005, visits in which a patient was seen by a provider and then was referred or returned to the referring provider were subclassified into five categories depending on the type of referral. Beginning in 2005, these categories were consolidated, which resulted in time inconsistency. To create a time-consistent classification, discharge status was recoded into the following categories: admitted to the hospital as an inpatient, transferred to another facility, admitted for an observation stay (that is, less than 24 hours), seen by a provider and released (includes all outpatient referrals, return if needed, return by appointment, and no follow-up planned), left before being seen or against medical advice, and other (includes discharges that were coded "no answer" and "other" by NCHS).
Source of payment. The primary source of payment for the visit was categorized as private, Medicare, Medicaid, other coverage, self-pay or charity, or unknown.
Demographic indicators. Patient age, gender, and race-ethnicity (white, black, Hispanic, or other) were used in analyses.
Medical diagnostic services and interventions. Persons seeking mental health care in emergency departments may receive medical diagnostic services (for example, blood glucose tests or CAT scans) or medical interventions (for example, intravenous fluids) before receiving any specialty mental health care (
13 ). Receipt of medical care plus mental health care might account for differences in the duration of mental health and non-mental health visits. To adjust for receipt of medical care, we included three covariates: the total number of common medical diagnostic services provided (range 0 to 21), the total number of common medical procedures (range 0 to 11), and whether the visit was related to an injury or poisoning.
Immediacy of need. Patients who are judged to have a more immediate need for medical attention at the time of admission may be seen sooner, and consequently they may have shorter visits. Four indicators derived from the admission record were included: the admitting provider judged that the patient should be seen within one hour from the time of admission; the patient was not oriented to time, place, and person; the patient's mode of arrival was by ambulance or by public service (police, social service, or beach patrol or escorted by another public service official) versus a "walk-in" (the patient arrived by car, taxi, bus, or foot); and the admitting provider rated the patient as being in moderate or severe pain.