Sign the Resolution
Contents | Feedback | Search
DRCNet Home | Join DRCNet
DRCNet Library | Schaffer Library | Government Publications

Sourcebook of Criminal Justice Statistics

Appendix 10

Drug Abuse Warning Network

Methodology, estimation procedures, and data limitations

This information was excerpted from U.S. Department of Health and Human Services, Substance Abuse and Mental Health Services Administration, Year-End Preliminary Estimates from the 1996 Drug Abuse Warning Network , Drug Abuse Warning Network Series: D-3 (Rockville, MD: U.S. Department of Health and Human Services, November 1997), pp. 3, 20-23; and Annual Emergency Department Data, 1994 (Rockville, MD: U.S. Department of Health and Human Services, October 1996), pp. 1-6. Non-substantive editorial adaptations have been made.

Methodology

These data were collected by the Substance Abuse and Mental Health Services Administration through the Drug Abuse Warning Network (DAWN). The data are weighted estimates representing all drug abuse-related emergency department episodes in the 48 contiguous States, the District of Columbia, and 21 metropolitan areas for calendar years 1993 through 1996. For 1996, 452 sample hospitals provided data to DAWN. These data yielded an estimated total of 487,564 drug-related episodes and 860,260 drug mentions. The table below details hospital participation in DAWN and the estimates of total drug-related episodes and drug mentions for 1993-96.

Hospitals eligible for DAWN are non- Federal, short-stay general surgical and medical hospitals in the coterminous United States that have a 24-hour emergency department. The American Hospital Association's (AHA) 1984 and 1985 Annual Surveys of Hospitals were used to obtain a sampling frame. Hospitals in the frame were stratified according to size; hospitals reporting 80,000 or more annual emergency department visits were assigned to a single stratum and selected with certainty. Additional strata were defined according to whether the hospital had an organized outpatient department or a chemical/alcohol inpatient unit. Twenty-one Metropolitan Statistical Areas were designated for oversampling and hospitals outside these areas were assigned to the national panel and sampled. In addition to the other strata, hospitals in the metropolitan areas were classified as to whether they were inside or outside the central city. A sample maintenance procedure was developed to randomly select "newly eligible" hospitals from the AHA each year using the same selection probabilities. This procedure allows the sample to be kept up-to-date and representative of over 5,000 DAWN-eligible hospitals in the coterminous U.S.

The national response rate was 74% in 1996; this rate is based on the number of eligible hospitals in the sample and the number actually responding. Data from the 21 oversampled metropolitan areas were pooled with data from the national panel to produce the national estimates.

For the purpose of reporting to the DAWN system, drug abuse is defined as the nonmedical use of a substance for psychic effect, dependence, or suicide attempt/gesture. Nonmedical use includes: the use of prescription drugs in a manner inconsistent with accepted medical practice; the use of over-the-counter drugs contrary to approved labeling; or the use of any other substance (heroin, cocaine, marijuana, glue, aerosols, etc.) for psychic effect, dependence, or suicide.

Within each facility participating in the DAWN system, a designated DAWN reporter, usually a member of the emergency department or medical records staff, was responsible for identifying drug abuse episodes and recording and submitting data on each case. An episode report is submitted for each drug abuse patient who visits a DAWN emergency department. To be eligible for DAWN, a case must meet all four of the following criteria: 1) the patient was treated in the hospital's emergency department; 2) the patient's presenting problem(s) was induced by or related to drug use, regardless of whether the drug ingestion occurred minutes or hours before the visit; 3) the case involved the non-medical use of a legal drug or any use of an illegal drug; and 4) the patient's reason for taking the substance(s) included one of the following: dependence, suicide attempt or gesture, or psychic effects. Each report of a drug abuse episode includes demographic information about the patient and information about the circumstances of the episode. In addition to drug overdoses, drug abuse emergency department episodes may result from the chronic effects of habitual drug usage or from unexpected reactions. Unexpected reactions reflect cases where the drug's effect was different than anticipated (e.g., caused hallucinations). Up to four different substances, in addition to alcohol-in-combination, can be specified for each episode. It should be noted that alcohol is reported to DAWN only when used in combination with another drug. It also should be noted that episodes involving children under 6 years of age are not reported to DAWN.

A drug episode is defined as an emergency department visit that was directly related to the use of an illegal drug or the non-medical use of a legal drug for persons age 6 years and older. The number of emergency department episodes reported in DAWN is not synonymous with the number of individuals involved. One person may make repeated visits to an emergency department or to several emergency departments, thus producing a number of episodes. No patient identifiers are collected, therefore it is impossible to determine the number of individuals involved in the reported episodes.

A drug mention refers to a substance that was mentioned during a drug-related emergency department episode. In addition to alcohol-in-combination, up to four substances may be reported for each drug-related episode; thus, the total number of mentions exceeds the number of total episodes. It should be noted that a particular drug mention may or may not be the confirmed "cause" of the episode when multiple drugs have been mentioned. Even when only one substance is reported for an episode, allowance should still be made for reportable drugs not mentioned or for other contributory factors.

Estimation procedures

The data represent weighted estimates of total emergency department drug episodes and drug mentions in the coterminous U.S. and in the 21 metropolitan areas oversampled in DAWN. The weights are generated each quarter for each hospital in the sample and are the product of a four-component model that considers (1) the base sampling weight calculated as the reciprocal of the sampling probability; (2) an adjustment for atypical reporting, applicable to certain hospitals that merge, split, or respond in an unusual way; (3) an adjustment for nonresponse based either on complete nonparticipation or failure to provide data on all the reporting days in a given time period; and (4) a benchmark factor, applied within metropolitan areas, that adjusts the total number of emergency department visits among participating sample hospitals to the total for the population of hospitals as determined from the sampling frame.

Correction of the estimation system

In 1995, a comprehensive review and correction of the DAWN estimation system was completed. The changes have been fully implemented for the 1993 data. Estimates for 1993-96 reflect those changes as will subsequent years. Most of the errors were due to miscalculation of the weights of hospitals that had undergone organizational changes since they were selected into the sample. Estimates prior to 1993 are not directly comparable to the 1993-96 estimates presented in this edition of SOURCEBOOK.

Preliminary versus final estimates

Final estimates are produced once a year when all hospitals participating in DAWN have submitted their data for that year and when additional ancillary data used in estimation become available. The differences between preliminary and final estimates are due to several factors.

(1) Final estimates include data from a small number of late-reporting hospitals. Data from some late-reporting facilities are received for each time period. Therefore, later files will usually include more complete data (i.e., have a higher response rate).

(2) Additional hospitals are added to the sample and incorporated into the final estimates for a given year (not the preliminary estimates for that same year). Most of these hospitals are "newly eligible" because they became DAWN eligible sometime after the original sample was selected. The final DAWN estimates are produced after the most current AHA Annual Survey of Hospitals file is received. This file was used initially to establish a sampling frame for DAWN. Subsequently, the most current AHA file is used once a year to maintain the representativeness of the sample. Between the releases of the preliminary and final estimates, the use of the newer AHA survey can result in hospitals being added to the sample and incorporated into the final estimates.

(3) Data from the most current AHA file are used to produce the final weights.

While the final estimates differ from the preliminary estimates, in past years the basic conclusions have not changed.

Data limitations

When producing estimates from any sample survey, two types of errors are possible--sampling and nonsampling errors. The sampling error of an estimate is the error caused by the selection of a sample instead of utilizing a census of hospitals. Sampling error is reduced by selecting a large sample or by using efficient sample design and estimation strategies such as stratification, optimal allocation, and ratio estimation. Nonsampling errors occur from nonresponse, difficulties in the interpretation of the collection form, coding errors, computer processing errors, errors in the sampling frame, reporting errors, and other errors. Many procedures are in place to minimize nonsampling errors such as data editing and periodic retraining of data collectors. Further, nonrespondents are identified for additional recruitment. Late reporters are assigned for priority data collection and respondents with changes in reporting are designated for followup.

It also is important to recognize that DAWN does not provide a complete picture of problems associated with drug use, but rather focuses on the impact that these problems have on hospital emergency departments in the United States. If a person is admitted to another part of the hospital for treatment, treated in a physician's office or at a drug treatment center, the episode would not be included in DAWN.

Sourcebook of Criminal Justice Statistics