State and Local Surveillance Systems
Fatal firearm-related injury surveillance in Maryland

https://doi.org/10.1016/S0749-3797(98)00055-5Get rights and content

Abstract

Context: Maryland began a statewide firearm-related injury surveillance system in 1995. The system now focuses on firearm-related deaths; a system to monitor nonfatal injuries is being developed. The system is passive; it accesses, integrates, and analyzes data collected by Maryland’s Office of the Chief Medical Examiner, Maryland State Police, and Division of Health Statistics.

Objective: To evaluate the surveillance system’s ability to ascertain cases in the absence of a standard for the true number of cases.

Design: Link records of the same firearm-related death captured by the surveillance system’s multiple data sources, comparing the rate of false positives and false negatives, and assessing errors in linkage variables.

Setting: Maryland, 1991–1994.

Participants: All deaths occurring in the state of Maryland as a result of a firearm-related injury.

Main Outcome Measures: Sensitivity and positive predictive value.

Results: The system is extremely sensitive, detecting 99.61% of cases, and it has a very high positive predictive value, with 99.87% of the cases identified from medical examiner’s office data being confirmed as actual cases.

Conclusions: Maryland’s database of information from the medical examiner’s office is highly accurate for ascertaining firearm-related deaths that occur in the state. A unique identifier common across data sources would ease record linkage efforts, and improve the system’s ability to monitor firearm-related deaths.

Introduction

Firearms have been the leading cause of injury-related deaths in Maryland since 1991.1 It is one of only a few states where the number of firearm-related injury deaths exceeds the number of motor vehicle injury deaths.2 Mirroring national patterns, firearm-related deaths in Maryland disproportionately affect youths, males, and blacks. Although the overall age-adjusted rate of deaths from firearm-related injuries has remained stable since 1991 (about 15 per 100,000 residents), the rate of firearm-related deaths has increased nearly 17% among youths aged 15 to 24 years, from 29.5 deaths per 100,000 residents in 1991 to 34.4 per 100,000 in 1996.1 Firearm-related deaths are concentrated in two areas of the state: the city of Baltimore and Prince George’s County, a large county adjacent to Washington, DC. In 1996, 81% of firearm-related homicides and 63% of firearm-related deaths in the state occurred in these jurisdictions.1

These trends highlighted the need in Maryland for a statewide surveillance system to monitor the magnitude and composition of this important problem. Although mortality data collection efforts by the state medical examiner, state health department, and state police had been routine and well-accepted, the data had never been linked or subjected to case-by-case comparison. The Maryland Department of Health and Mental Hygiene began addressing these needs in 1995, when it created a passive surveillance system that monitors firearm-related deaths by accessing, integrating, and analyzing data collected by the Maryland Office of the Chief Medical Examiner and other state agencies. The system now monitors only fatal injuries, but a system to monitor nonfatal injuries is under development. The system addresses three primary concerns: the problem of firearm-related deaths in Maryland, the heavy concentration of firearm-related deaths in Baltimore and Prince George’s County, and the need for firearm-related data that could be used to evaluate the effectiveness of legislative initiatives such as the establishment of a handgun roster board, banning1of assault weapons, and most recently, passage of a law limiting firearm purchases to one gun per month.

The Maryland Firearm-Related Injury Surveillance System is designed to monitor the public health impact of firearm injuries and deaths and to provide a means for evaluating the effects of prevention policies in the future. In Phase I, which began in 1995, the system monitored firearm-related deaths. In Phase II, now under development, the system will begin also to monitor nonfatal firearm-related injuries, using information from hospital discharge data and emergency department sources. This article focuses only on the state’s current activities to monitor firearm-related deaths.

The surveillance system has two levels of coverage and detail for the collection of information on firearm-related deaths:

  • Level 1. The system ascertains all firearm-related deaths occurring in the state. Level 1 information is brief and basic, but it provides statewide coverage.

  • Level 2. The system focuses on firearm-related deaths in the city of Baltimore and Prince George’s County. The data include information about weapons and circumstances from police records on firearm-related fatalities. Level 2 information is highly detailed, but it covers only two areas within the state.

The firearm-related mortality surveillance system taps two sources of data: (1) data maintained by the state’s Office of the Chief Medical Examiner (OCME); and (2) Supplementary Homicide Reports (SHR), data compiled by the Maryland State Police. A third source of information, computerized death certificate data from the Maryland Department of Health and Mental Hygiene’s Division of Health Statistics, is also described, because it is used in this report as a basis for comparing all types of firearm-related deaths.

Maryland operates a statewide medical examiner system to certify deaths by homicide, suicide, and accident. It is also charged with investigating sudden deaths of persons in apparent good health or unattended by a physician, and any other deaths of a suspicious or unusual manner. The system is headed by the OCME. Deputy medical examiners in each county are responsible for the initial investigation and certification of deaths in their counties, and they may determine the cause of death. The OCME’s forensic pathology staff members perform autopsies when necessary to establish the cause of death. Because autopsies are required in all cases of homicide that occur in the state, the OCME staff members complete the records in these cases. In cases of suicide and unintentional death, autopsies are carried out when warranted by the circumstances. This involves discussion between the deputy medical examiners and OCME staff. If no autopsy is conducted, the deputy medical examiner completes the death record and forwards a copy to the OCME within 3 months of the death. The OCME database is thus designed to have a complete record of all homicides, suicides, and deaths due to unintentional and undetermined causes within 3 months of certification of death.

The OCME database was selected as the foundation for the surveillance system for two reasons: (1) it records the events in a timely manner; and (2) it is a relational database stored on a minicomputer that permits automated data extractions.

Maryland operates a law enforcement–based system for recording homicide data that is roughly parallel to the OCME homicide database. It relies primarily on voluntary submission of completed Uniform Crime Reporting forms from each police jurisdiction to the Maryland State Police.

Part of this system includes the SHR, a separate form requesting basic (individual-level) information on each victim of murder and nonvehicular manslaughter. The Maryland State Police’s Central Records Division is responsible for receiving and coding these paper reports. Each month, the surveillance system staff receives photocopies of SHRs from the Uniform Crime Reporting unit. To speed access to the data and to preserve textual comments not keyed into computers, the surveillance system staff performs its own entry of the data on each homicide victim. Thus, the SHR data are not as timely as those from the OCME’s file. The OCME database includes data on homicides within 3 to 4 days of examination; the SHR data are compiled monthly. Maryland has no statewide, police-generated database providing basic SHR-type information on suicide.

The Maryland Department of Health and Mental Hygiene’s Division of Health Statistics maintains the state’s mortality statistics database, which includes information on deaths due to firearm-related causes. Death certifiers forward copies of death certificates to the Division of Health Statistics where the data are coded and entered into computer files. This office then assigns cause-of-death classifications, according to International Classification of Diseases, 9th Revision (ICD) definitions. Death certificate data are not used for firearm-related surveillance because they become available only after an extended period of time (usually 6 months to a year after death). Because timeliness is an important feature in any surveillance system, the death certificate data are not part of the main surveillance database but rather are used for retrospective evaluations of the system.

The surveillance system is intended to capture all fatal firearm injuries occurring within Maryland. In addition to detecting firearm-related deaths, the surveillance system also captures nonfirearm-related homicides and suicides to provide a baseline for comparison. A firearm-related death is defined as any fatal injury resulting from the discharge of a weapon from which a projectile is propelled by explosives. Manner of death is the term used to distinguish homicide, suicide, unintentional fatal injury, and fatal injury of undetermined manner. Suicide is any intentionally self-inflicted fatal injury. Firearm-related deaths of undetermined manner are those that are pending classification or those that cannot be classified as homicides, suicides, or unintentional deaths. The definition of homicide varies according to data source. According to the OCME, homicide is death resulting from an act or an omission by another person. Homicide, thus defined, includes legal interventions (law enforcement officials acting in the line of duty), intentional deaths by civilians that may be legally justifiable or excusable, and unintentional killings of persons by other persons. Motor vehicle crash–related deaths caused by other persons are not classified as homicides. In homicide data based on police sources, a distinction is usually made between criminal and noncriminal homicide. Criminal homicide includes murder, non-negligent manslaughter, and manslaughter due to gross negligence. Unintentional firearm-related deaths are those that result from unintentional events or that are otherwise not purposeful.

Because this surveillance system is passive, its methods are simple. At regular intervals, the surveillance system accesses data that meet the case definition criteria, standardizes data formats across sources, links data records across sources when appropriate, and focuses analysis and reporting on firearm-related injury events (Figure 1 ).

Every week (or other desired interval), surveillance system staffers perform the following steps to access data on firearm-related deaths. First, staff members travel to the OCME offices in Baltimore, access the main computer, and modify the query program to specify the appropriate date range to be covered. The query then extracts all data on homicides, suicides, unintentional firearm-related deaths, and other firearm-related deaths in which the manner of death is undetermined for the period of interest.

Each month, project staff receive photocopies of SHR forms from the Maryland State Police. Victim-level information on the forms is then keyed into the computer and translated into a compatible analysis format.

Finally, to verify the weekly and monthly data, the surveillance system staff acquires death certificate data from the state’s Division of Health Statistics once a year. Also each year, staff members download U.S. Bureau of the Census population estimates from the Internet for the purpose of computing firearm-related death rates.

OCME and SHR data on homicides represent essentially the same events, but each source provides different characteristics of these events. For example, the OCME data include information on the number of gunshot wounds and the presence of drugs or alcohol in the body, whereas the SHR data include information on the type of weapon, victim-offender relationship, and circumstances surrounding the incident. Thus, linking the OCME and SHR data provides a more complete picture of the event than either source alone would provide.

It is difficult to link records on a case-by-case basis using a computer. To do this, one needs to recode the data in the two sources so that the structures of key matching variables are the same across files. In theory, two files from the same information domain can be matched perfectly if (1) the cases in each file can be uniquely identified by a common variable or set of variables, and (2) the common identifier variables contain no errors or at least no inconsistencies between them. As a practical matter, however, common unique identifiers across official record systems do not generally exist. Even when a direct identifier such as decedent name is available in both files, the information can be (and often is) recorded with error. Unfortunately, even a small variation in an identifier (like a misspelled name) causes problems for most computer matching routines. Probabilistic record linkage procedures designed to address these problems exist,3 but we did not have access to them at the time of this study. Thus, we manually matched records. These procedures are described later, in the Evaluation Design section.

An annual data report and monthly updates are disseminated by the Department of Health and Mental Hygiene’s Office of Public Information, both by press release and by targeted mailings to interested individuals and organizations within the state. In addition, surveillance system staff prepare briefing materials for health officials, testify before legislative committees and task forces, and respond to other data requests (primarily from the media) as they arise. The principal use of the data is for education. The data are also being used to evaluate the effectiveness of legal policy interventions in the state. (See Sidebar Firearm-Related Deaths in Maryland: At A Glance for a summary of recent findings.)

Section snippets

Evaluation design

Our evaluation strategy is to link records across parallel data sources to assess the completeness of the system. The procedure is simple. We manually link OCME data with vital statistics (VS) data from death certificates. In selecting VS data as a source of comparison with OCME data, we assume that death certificates are issued and forwarded to the Division of Health Statistics for every death that occurs in the state. In other words, every OCME record of firearm-related death should have a

Aggregate analysis

In every year from 1991 through 1994, the annual difference recorded between the OCME and the VS ranged from 4 to 11 deaths, but the VS total never exceeded the OCME total (see Total column in Table 1 ). To better understand this relationship, we must decompose the aggregate totals by manner of death. When we break down the totals by homicide, suicide, unintentional, and manner undetermined for 1991 to 1994 (see pertinent columns in Table 1), the pattern of results is considerably more complex

Conclusions

In evaluating the Maryland surveillance system we have learned that the completeness of a firearm-related mortality surveillance system should be measured, and not assumed, because no gold standard for comparison has been established for these events (see Lessons Learned). Had we assumed the VS data were an accurate standard for comparison, we would have drawn erroneous conclusions about the sensitivity and predictive value positive of the OCME data for identifying firearm-related deaths, at

Lessons learned

  • Do not assume the completeness of data in a firearm-related injury surveillance system.

  • E-coding of firearm-related injuries may result in underreporting of firearm-related events because some E codes do not accurately distinguish firearm-related injuries from those that do not involve firearms. Pay attention to E codes for late effects of injuries.

  • If possible, encourage the use of a common, unique identifier across data sources to increase record linkage efficiency and accuracy.

  • If a common

Firearm-related deaths in Maryland: at a glance

Firearm-related injuries are the leading cause of injury deaths occurring in the State of Maryland. They exceed deaths due to motor vehicle injuries. In 1991, Maryland was one of only six states in the United States in which firearm-related mortality equaled or exceeded motor vehicle–related injury mortality.

Since 1991, the overall age-adjusted rate of deaths from firearm-related injuries has remained stable: about 15 per 100,000 residents.

Young people (persons aged 15 to 24 years) have the

Acknowledgements

This evaluation was supported by the Centers for Disease Control and Prevention, National Center for Injury Prevention and Control (grant no. U17/CCU311058). For their help with this evaluation, we thank Denise V. Scherer, Uniform Crime Reporting Program, Maryland State Police; Shirley M. Fennell, Shirl K. Walker, and Ann Dixon, MD, Office of the Chief Medical Examiner, State of Maryland; Isabelle L. Horon, DrPH, and Roy Tansill, Division of Health Statistics, Maryland Department of Health and

References (4)

  • Wiersema B, Loftin C, Daub EM, Sheppard MA, Smialek JE. Firearm-related mortality in Maryland, 1976–1996. Baltimore,...
  • Fingerhut LA, Jones C, Makuc DM. Firearm and motor vehicle injury mortality-variations by state, race, and ethnicity:...
There are more references available in the full text version of this article.

Cited by (10)

  • Attempts to silence firearm injury prevention

    2012, American Journal of Preventive Medicine
View all citing articles on Scopus
View full text