Data and Terminology
state-by-state database was created
for the study that includes motor vehicle fatality
information, demographic and economic data, and
impaired driving laws and enforcement. This section
describes the specific items in the database and
their sources.
Drivers in fatal crashes. Data on fatal crashes
came from NHTSA's Fatality Analysis Reporting System
(FARS) and its supplemental Alcohol Imputation files.
FARS is an enumeration of virtually all fatal motor
vehicle crashes that occur in the U.S. The Alcohol
Imputation files are based on available BAC data
or use statistical methods to estimate (or impute)
whether or not a crash involved alcohol if there
is no direct evidence of alcohol presence or absence.
The Alcohol Imputation files
The Alcohol Imputation files are made up of two
parts. The part used in this study contains probability
values that each driver and nonoccupant in a fatal
crash had a BAC of 0.00, a BAC of 0.01-0.09, and
a BAC of 0.10 or more. The second part contains
probability values at the crash level. That is,
based on the driver and nonoccupant probabilities,
a probability value is estimated that the crash
involved drivers and nonoccupants with only 0.00
BAC, that the crash involved at least one driver
or nonoccupant with a BAC in the 0.01-0.09 range
but none higher, and that the crash involved at
least one driver or nonoccupant with a BAC of 0.10
or higher. For both parts, when a driver or nonoccupant
has a known BAC (zero or positive), that BAC value
is used. When the BAC is unknown, a discriminant
function model estimates the probabilities that
the person's BAC was in the three categories. The
variables entered into the discriminant function
are those from the FARS database (vehicle type,
police reported alcohol, time, day of week, driver
age and sex, etc.). The imputation methodology is
described by Klein (1986a) and a guide for using
the imputation files can be found in Klein (1986b).
FARS
FARS has used the Alcohol Imputation process since
1982. For this study, drivers in fatal crashes have
been examined over the 17-year period 1982-1998.
The data used in the analyses for 1998 are from
the preliminary file, as the final 1998 version
had not been released when these analyses were completed.
The preliminary data for 1998 indicated that there
were 8,116 drivers under the age of 21 involved
in fatal crashes, with 1,704 of these determined
to have been drinking. The final FARS version for
1998 shows that there were 8,128 drivers under the
age of 21 involved in fatal crashes, with 1,714
of these determined to have been drinking.
Some states do not use these estimated data to
report alcohol-related traffic fatalities. Instead,
they count as alcohol-related only those crashes
and drivers for which there is positive evidence
from a BAC test, a police report, or another official
source. These states will report a lower number
of alcohol-related traffic fatalities and alcohol-related
drivers in fatal crashes than the FARS estimates.
In addition, some states use a different definition
of alcohol-related, such as by including only crashes
in which a driver had a BAC of 0.10 or greater.
The FARS data were used in this study to assure
that all states were compared on a common basis.
While some states report different alcohol-related
traffic fatality totals than FARS, in general the
trends in FARS and state data are very similar.
Trends also are similar regardless of what definition
is used (total fatalities or drivers above 0.10
BAC, for example).
Data on Canadian fatal crashes were graciously
provided by the Traffic Injury Research Foundation
(TIRF), Ottawa (Beirness, 2000). The TIRF Fatality
Database is supported financially by the Canadian
Council of Motor Transport Administrators and Transport
Canada.
Economic and Demographic Factors, and Laws
Population Data.
The Bureau of the Census produces
various annual estimates of the U.S. population.
For this study, the most useful was the annual Estimates
of the Population of the U.S. and States by Single
Year of Age and Sex. Data on population by age in
each state for the period 1982-1998 were compiled.
Economic Data. Annual state-by-state data were
obtained from the Bureau of Labor Statistics on
the number of persons employed, the number not employed,
and the number not in the labor force for 1982-1997.
State Laws. NHTSA provided the dates when different
traffic and alcohol laws became effective in each
of the states.
Alcohol Consumption. Published data were obtained
from the National Institute of Alcohol Abuse and
Alcoholism (NIAAA) and the Beer Institute of America.
DWI and Liquor Law Violations. Data were obtained
from the Federal Bureau of Investigation (FBI) Uniform
Crime Reporting System.
Data on Drinking and Drinking-related Behavior
Monitoring the Future. The best data on youth drinking
and drinking-related behavior come from the ongoing
Monitoring the Future study. Approximately 17,000
high school seniors, from a nationally representative
sample of about 135 schools, have provided confidential
self-reported information on alcohol and drug use
and related behavior each year since 1975. Results
are reported annually (most recently in Johnston,
O'Malley, and Bachman, 1999). Questions on drinking
and driving have been included since 1984 for one-sixth
of the sample. O'Malley and Johnston (1999) summarize
and discuss these data and trends. Data for this
study were obtained from Johnston, O'Malley, and
Bachman (1999) and O'Malley (2000).
College Age Youth Surveys.
While there are no ongoing
surveys of college students comparable to Monitoring
the Future, two studies provide information on college
students' drinking and drinking-related problems,
including driving after drinking, at several points
in the past 20 years. Hanson and Engs (1992) surveyed
approximately 4,000 students at 65 representative
4-year colleges in 1982, 1985, 1988, and 1991. Wechsler,
Davenport, Dowdall et al. surveyed 17,552 students
at 140 nationally-representative 4-year colleges
in 1993.
General Public Surveys.
Three other surveys provide
useful information on drinking or drinking and driving
for both young and other persons since 1980. Balmforth
(1998) reports results from nationally representative
surveys of approximately 4,000 persons age 16 and
older in each of the years 1991, 1993, 1995, and
1997. Balmforth aggregates results into the age
groups 16-20 and 21-29. Caetano and Clark (1997)
surveyed nationally-representative samples of 1,947
black, 1,453 Hispanic, and 1,777 white adults (age
18 and older) in 1984 and 1,582 blacks, 1,585 Hispanics,
and 1,636 whites in 1995. Midanik and Clark (1994)
surveyed 2,058 adults in a national household probability
sample in 1990 and compared their results with data
from 5,221 respondents in a 1984 national alcohol
survey. The latter two studies aggregate results
for the age group 18-29.
D. Terminology
The following terms and abbreviations are used throughout
the report.
BAC - alcohol content in the body, originally measured
using alcohol in blood (BAC stood for Blood Alcohol
Content, expressed in milligrams of alcohol per
100 milliliters of blood), now typically measured
using alcohol in breath.
Drinking Driver - a driver involved in a traffic
fatality who is estimated to have a positive BAC
(as reported by FARS).
DWI - the offense of driving while impaired by
alcohol. The formal offense differs from state to
state (Driving While Impaired, Driving While Intoxicated,
and Driving Under the Influence are common). Here,
DWI will be used to describe each state's standard
impaired driving offense.
Youth (or young driver) - a person (or driver)
under 21 years of age.
