________________________________________________________________________

_______ National Center for Statistics and Analysis, 400 Seventh St., S.W., Washington, DC 20590 1

DOT HS 809 450 Estimates of Alcohol Involvement in

Fatal Crashes

U.S. Department of Transportation

National Highway Traffic

Safety Administration

Introduction

The National Highway Traffic Safety Administration (NHTSA) has adopted a new method to

estimate missing blood alcohol concentration (BAC) test result data. This new method, multiple

imputation, will be used by NHTSA’s National Center for Statistics and Analysis (NCSA) to

improve the scope of alcohol involvement statistics generated by the Fatality Analysis Reporting

System (FARS).

The old estimation method used by NHTSA calculated the chance that a driver, pedestrian or a

pedalcyclist with unknown or missing alcohol results had a BAC in each of the three categories:

0, 0.01 to 0.09, or 0.10 and greater. Beginning with the 2001 data, NCSA will use multiple

imputation to estimate missing BAC values in FARS. Multiple imputation offers NHTSA

significant advantages over the old method in analyzing and reporting estimates of alcohol

involvement. Instead of estimating alcohol involvement by the three aforementioned categories,

the new method will estimate BAC along the entire range of plausible values (0 to 0.94 g/dl).

Estimating missing BAC this way will enable NHTSA to report the extent of alcohol

This fact sheet is intended to inform NHTSA’s partners of this methodology change, and to

compare estimates of alcohol involvement using the old and new methods, as well as to address

anticipated questions.

Alcohol Involvement: Comparing Estimates from the New and Old Methods

Chart 1 shows the estimated extent of alcohol-related fatalities from 1982-2000 based on the new

and old methods of BAC estimation.

35

40

45

50

55

60

65

1982198319841985198619871988198919901991199219931994199519961997199819992000

Percent of Fatalities

New Old

Chart 1: Alcohol-Related Fatalities as a Percentage of Total Fatalities, 1982-2000

New Alcohol Methodology

involvement at any BAC level.
________________________________________________________________________

_______ National Center for Statistics and Analysis, 400 Seventh St., S.W., Washington, DC 20590 2

National Estimates:

Table 1 shows the estimated rates of alcohol involvement among drivers involved in fatal crashes

as estimated using the two methods from 1982-2000. The numbers in Table 1 reflect the

percentage of all drivers (killed or survived) who had a BAC of 0.01 or greater. Table 2 shows

the percentage of all fatally injured pedestrians and pedalcyclists who had a BAC of 0.01 or

greater.

Table 1: Alcohol Involvement Among

Drivers in Fatal Crashes by their

Survival Status: A Comparison of

Estimates Using the New and Old

Methods, 1982-2000*

Year Killed

New Old

Survived

New Old

Total

New Old

1982 55 53 29 28 41 39

1983 54 51 28 27 39 38

1984 51 49 27 25 38 36

1985 49 48 23 23 35 34

1986 50 48 25 23 36 34

1987 48 47 23 23 34 33

1988 47 47 22 22 33 33

1989 46 46 20 21 31 32

1990 46 46 23 21 33 32

1991 45 44 21 21 31 31

1992 43 42 19 19 30 29

1993 41 40 18 18 28 27

1994 38 37 18 16 27 25

1995 39 38 16 16 26 25

1996 38 37 16 16 26 25

1997 36 35 15 15 24 24

1998 36 35 15 15 24 23

1999 36 35 14 14 24 23

2000 37 36 16 15 26 24

*Based on 1982-1999 Final FARS Files and

2000 Annual Report File

Table 2: Alcohol Involvement Among

Fatally Injured Pedestrians and

Pedalcyclists: A Comparison of

Estimates Using the New and Old

Methods, 1982-2000*

Year Pedestrians

New Old

Pedalcyclists

New Old

1982 42 41 22 20

1983 42 40 18 20

1984 40 39 18 18

1985 40 39 15 18

1986 39 39 17 18

1987 38 38 19 21

1988 37 37 18 19

1989 39 39 18 19

1990 38 38 20 21

1991 38 38 24 24

1992 39 38 20 22

1993 38 37 22 23

1994 36 36 20 21

1995 37 37 23 24

1996 38 38 22 23

1997 35 34 22 23

1998 38 37 24 24

1999 38 37 26 26

2000 38 37 25 26

*Based on 1982-1999 Final FARS Files and

2000 Annual Report File

The NHTSA Technical Reports cited at the end of this document offer a more technical view into

the new method and have detailed tabulations of alcohol involvement in various categories (age,

sex, time of day, etc.). The reports compare the estimates from both methods for each category.

The overall trend of alcohol involvement is similar for the estimates from both methods. At the

national level, differences between the estimates tend to be two percentage points or less. For

smaller sub-populations such as states, age groups, etc., estimates from the two methods will

differ. This variation can be attributed to the inherent differences in the way the two processes

work and because the new method employs a more rigorous procedure of defining the

relationship between BAC and the factors that predict BAC. Additionally, the sensitivity of the

estimates depends on how much data is missing. The difference between the estimates produced

by the two methods tends to be greater in states that have very low BAC reporting levels.
________________________________________________________________________

_______ National Center for Statistics and Analysis, 400 Seventh St., S.W., Washington, DC 20590 3

State-level Alcohol Estimates:

Table 3 compares the estimates of alcohol-related fatalities by state from 1998-2000. Table 4

compares the extent of alcohol involvement among drivers involved in fatal crashes by state from

1998-2000. As shown in Tables 3 and 4, although there is a minor shift in the extent of alcohol

involvement from 1998-2000 in most states, the year-to-year changes appear to be similar using

both estimation methods. For example, if the extent of alcohol involvement increases each year

in a given state from 1998-2000 using the old method, then this will likely be true using the new

method as well.

Table 3: Fatalities in Alcohol-Related Crashes: A Comparison of Estimates

Using the New and Old Methods, 1998-2000*

Percentage with BAC 0.01 g/dl or Greater

State 1998

New Old

1999

New Old

2000

New Old

State 1998

New Old

1999

New Old

2000

New Old

Alabama 41 38 41 38 43 40 Montana 44 44 49 47 49 46

Alaska 44 45 51 52 54 52 Nebraska 38 38 43 42 38 37

Arizona 45 43 41 40 45 44 Nevada 49 49 44 45 43 45

Arkansas 35 31 35 31 34 31 New Hampshire 49 48 47 49 37 39

California 39 38 39 38 39 37 New Jersey 36 35 39 40 44 44

Colorado 39 37 37 35 40 38 New Mexico 46 45 45 45 49 48

Connecticut 44 43 45 45 47 46 New York 30 26 30 27 32 29

Delaware 40 39 42 40 50 49 North Carolina 36 35 38 36 39 36

DC 57 51 57 53 38 39 North Dakota 50 47 49 47 49 48

Florida 37 33 39 36 43 40 Ohio 37 33 37 35 41 38

Georgia 34 33 35 34 38 37 Oklahoma 35 33 35 33 36 34

Hawaii 49 49 45 44 43 41 Oregon 43 43 42 41 41 42

Idaho 38 34 37 36 43 41 Pennsylvania 43 42 40 38 43 41

Illinois 44 43 44 44 44 43 Rhode Island 49 48 41 41 52 51

Indiana 41 39 38 36 34 31 South Carolina 37 31 37 31 41 40

Iowa 36 37 34 33 30 28 South Dakota 41 41 44 43 48 47

Kansas 34 32 36 34 35 33 Tennessee 42 41 40 38 43 39

Kentucky 36 33 37 35 34 31 Texas 49 50 48 50 49 50

Louisiana 48 47 47 46 49 48 Utah 18 14 25 21 28 24

Maine 28 28 33 32 31 30 Vermont 38 37 39 38 41 39

Maryland 37 34 36 34 40 38 Virginia 38 37 38 36 38 37

Massachusetts 45 48 47 49 49 50 Washington 47 46 43 42 45 44

Michigan 40 39 41 40 38 37 West Virginia 42 41 38 37 45 43

Minnesota 44 43 33 32 41 41 Wisconsin 43 42 42 41 44 43

Mississippi 38 37 40 39 41 40 Wyoming 46 44 38 37 32 30

Missouri 44 45 40 40 44 44 U.S. Total 40 39 40 38 41 40

*Based on 1998-1999 Final FARS Files and 2000 Annual Report File
________________________________________________________________________

_______ National Center for Statistics and Analysis, 400 Seventh St., S.W., Washington, DC 20590 4

Table 4: Alcohol Involvement Among Drivers Involved in Fatal Crashes: A

Comparison of Estimates Using the New and Old Methods, 1998-2000*

Percentage with BAC 0.01 g/dl or Greater

State 1998

New Old

1999

New Old

2000

New Old

State 1998

New Old

1999

New Old

2000

New Old

Alabama 26 24 26 24 29 26 Montana 32 32 40 38 33 32

Alaska 32 32 35 36 40 38 Nebraska 27 27 27 27 23 23

Arizona 26 24 22 21 26 25 Nevada 30 30 27 27 30 31

Arkansas 22 19 24 21 23 21 New Hampshire 29 28 34 35 29 30

California 22 21 22 22 22 21 New Jersey 21 21 22 23 24 25

Colorado 24 23 23 23 24 22 New Mexico 29 29 28 29 29 28

Connecticut 29 29 29 29 32 30 New York 17 15 17 15 18 16 

Delaware 21 20 21 20 31 29 North Carolina 19 18 21 19 24 21

DC 35 32 35 32 24 24 North Dakota 36 35 35 33 39 38

Florida 19 17 20 19 24 22 Ohio 23 20 22 21 26 24

Georgia 20 19 20 19 22 22 Oklahoma 23 22 22 21 22 21

Hawaii 30 29 30 29 27 25 Oregon 27 27 25 24 24 24

Idaho 24 22 26 25 30 28 Pennsylvania 28 26 25 24 27 25

Illinois 26 25 26 26 27 26 Rhode Island 33 32 29 29 38 37

Indiana 26 25 23 22 22 19 South Carolina 22 18 22 18 26 26

Iowa 22 23 21 20 19 17 South Dakota 29 27 30 30 30 29

Kansas 23 22 24 22 23 22 Tennessee 26 25 26 25 27 25

Kentucky 22 20 24 23 23 20 Texas 31 32 30 32 31 33

Louisiana 30 29 31 31 32 32 Utah 12 9 18 14 19 16 

Maine 20 19 21 21 20 19 Vermont 27 26 27 26 31 30

Maryland 20 19 20 19 21 21 Virginia 24 23 24 23 24 22

Massachusetts 29 31 31 33 31 32 Washington 29 28 28 27 29 28

Michigan 24 23 24 23 22 21 West Virginia 27 26 24 23 31 29

Minnesota 27 26 20 19 26 26 Wisconsin 27 27 28 28 28 27

Mississippi 27 26 26 27 28 27 Wyoming 35 34 27 26 23 22

Missouri 28 28 26 26 28 28 U.S. Total 24 23 24 23 26 24

*Based on 1998-1999 Final FARS Files and 2000 Annual Report File
________________________________________________________________________

_______ National Center for Statistics and Analysis, 400 Seventh St., S.W., Washington, DC 20590 5

Frequently Asked Questions (FAQ)

This section answers some of the most frequently asked questions about the change to the

new methodology. NHTSA reports that explain the technical details of the new

methodology are listed in the Further Information section at the end of this fact sheet.

1. What is the proportion of the cases in FARS that do not have a known BAC? 

A. On an average, approximately 60 percent of the Blood Alcohol Concentration (BAC) values 

for Drivers, Pedestrians and Pedalcyclists are missing in FARS each year as a result of 

alcohol tests not being administered or test results not being reported. 

2. How do you address the problem of missing information? 

A. Imputation is the practice of ëfilling in‛ missing data with plausible values using proven, 

scientific methods. The ideal scenario for any database like FARS is to have a variable 

(e.g., BAC) known for all the records. However, important variables are often missing 

from crash data, and so estimated values are used instead of unknown or blank values, 

enabling valid conclusions to be made. 

3. Why impute Missing BAC in FARS? 

A. If estimates of alcohol involvement are based only on BAC values that are reported for 

some persons, invalid inferences will result because the characteristics of the persons 

with unknown BACs can be significantly different from those with reported BACs. 

4. What is Multiple Imputation (MI)? 

A. MI is a proven technique in which each missing value in a dataset is replaced by more than 

one simulated version using rigorous statistical techniques. These techniques establish 

the inter-relationships between the characteristics (variables) of cases with reported 

values. These relationships are then applied on the same set of variables in the cases 

where the missing values are to be imputed. Multiple values of the missing item are then 

generated.

5. Why use MI in FARS? 

A. For each missing BAC value in FARS, MI simulates actual values of BAC in the plausible 

range (0<=BAC<=0.94). This makes it possible to analyze the extent of alcohol 

involvement at any level of BAC (e.g., 0.07+, 0.08+, etc.). MI also allows for the 

computation of Standard Errors and Confidence Intervals, which enable NHTSA to 

report measures of statistical confidence about the generated estimates. 

6. Can the new estimates be used in regression analysis or other analysis? 

A. Yes, since the new estimates are actual values of BAC. 

7. Why are there differences between the results from MI and the old method? 

A. The imputation methodologies employ different statistical models to estimate missing 

BAC values. The old method computes the chance of involvement along definite categories 

(0, 0.01 to 0.09, and 0.10+) of BAC while MI imputes actual values of BAC (0 to 0.94). 

The MI estimates are generally between 0 to 2 percentage points higher than the 

estimates from the old methodology.
________________________________________________________________________

_______ National Center for Statistics and Analysis, 400 Seventh St., S.W., Washington, DC 20590 6

Conclusion

NHTSA will use the new procedure for estimating missing BAC values because of the

significant analytical advantages it provides over the earlier method. Multiple imputation

enables NHTSA to better support changing legislative needs such as the adoption of 0.08

as the illegal BAC level. The overall trend of alcohol involvement is similar for the

estimates from both methods, though minor differences exist when estimating alcohol

involvement in small sub-populations. The standard errors now available from using the

new estimation method will enable NCSA to provide statistical measures of confidence

about the imputed estimates.

Further Information

The following publications provide more detailed information and can be requested from

NHTSA through the contact information given below:

1. Rubin, D.B., Schafer, J.L., and Subramanian, R. (1998) Multiple Imputation of

Missing Blood Alcohol Concentration (BAC) values in FARS, Report DOT-HS808-816, National Highway Traffic Safety Administration, Department of

Transportation.

(This report presents an in-depth technical view of the multiple imputation process and its

implementation in the FARS system. Detailed specifications of the statistical models used to

estimate missing BACs are provided. Examples are also given of how the new data can be

analyzed and used in models.)

2. Subramanian, R. (2002) Transitioning to Multiple Imputation: A New Method to

Estimate Missing BAC in FARS, Report DOT-HS-809-403, National Highway

Traffic Safety Administration, Department of Transportation.

http://www-nrd.nhtsa.dot.gov/pdf/nrd-30/NCSA/Rpts/2002/809-403.pdf

(This report has detailed tabulations of the extent of alcohol involvement from 1982 to 2000 using

estimates generated with both the old and new methods. Alcohol Involvement is reported

according to various categories of interest (age, sex, time of day, day of week, etc.)

Contact Information

National Center for Statistics and Analysis

United States Department of Transportation

National Highway Traffic Safety Administration

400 Seventh Street, S.W.

Washington, DC 20590

Automated Information Request Line: 1-800-934-8517

In the Washington, D.C. area: 202-366-4198

Fax: 202-366-7078

E-mail: ncsaweb@nhtsa.dot.gov

Internet Site: http://www-nrd.nhtsa.dot.gov/departments/nrd-30/ncsa/