March 2005 DOT HS 809 860

Calculating Lives Saved Due to Minimum 

Drinking Age Laws

John Kindelberger*

Traffic Safety Facts

Research Note

NHTSA’s National Center for Statistics and Analysis 400 Seventh St., S.W., Washington, D.C. 20590

Currently (2004), every State in the United States prohibits 

purchase or public possession of alcoholic beverages for 

those under the age of 21. Each year, the National Center 

for Statistics and Analysis (NCSA) of the National Highway 

Traffic Safety Administration (NHTSA) publishes an estimate1

of lives saved due to such bans, referred to more generically 

as “minimum legal drinking age” (MLDA) laws. This note 

describes the methodology used, and introduces a slight 

change in that methodology. The described change will be 

implemented for the first time in the calculation of the estimate 

of number of lives saved during the year 2003.

Background

Between 1970 and 1975, 29 States lowered their drinking ages 

to 18, 19, or 20. By 1983, safety concerns had led many of 

these States to reverse course. In 1984, the Uniform Drinking 

Age Act reduced Federal transportation funding to States 

not prohibiting alcohol “purchase and public possession” 

for those under age 21. All States eventually restored their 

legal ages for alcohol purchase and public possession to 21 

years. 

NHTSA published an analysis in 19852 and a follow-up in 

19893 on the reduction in fatal crash involvements of drivers 

affected by an increase in the MLDA. The estimated number 

of lives saved is based on the reduction in target (18-20 years 

of age) driver involvements and the numbers of fatalities in 

crashes with those involvements. Thus “lives saved” in this 

context refers not to a reduction in young driver fatalities, but 

in all fatalities, driver or passenger, young or old, regardless 

of alcohol involvement, in crashes where at least one driver 

was in the targeted age group. NHTSA considers this method 

reasonable since it is not only young drivers who can be killed 

in their crashes, but indeed any passenger in any involved 

vehicle, as well as nonmotorists. 

The studies found that the target involvements decreased on 

average by 13 percent in States where the drinking age had 

been raised. Thus NHTSA’s effectiveness rating of a raised 

MLDA is 13 percent. The methodology of the effectiveness 

study can be found in Arnold.2 The cumulative estimated 

number of lives saved through 2002, based on Arnold’s 

methodology, is displayed in this note’s appendix.

Calculation

NCSA calculates its estimate of lives saved due to MLDA 

laws as follows:

Let F = the actual number of fatalities in target crashes 

recorded in NHTSA’s Fatality Analysis Recording System 

(FARS); 

Let P = potential fatalities: the number of fatalities that would 

have been expected in target crashes absent the MLDA 13 

percent effect 

P is computed from F by finding the number which, when 

reduced by 13 percent, gives F. Thus F must be (1-.13)*P, or 

87 percent of P, so

(1 - .13)*P = F, and P = F/(1-.13).

The estimated number of lives saved is then 13 percent of 

P, so

Lives Saved = (.13)*P = (.13)*F/(1-.13).

The lives saved calculation can also be developed from 

(P – F) with the same result.

Method Update

One group of crashes not accounted for in past estimates 

has been the group of crashes with no known drivers of 

the target age but at least one driver of unknown age. To 

ignore them assumes that none of the drivers of unknown 

age were in the target age group. In other estimates of lives 

saved due to various safety measures such as safety belts 

and air bags, NCSA’s standard practice is to allocate relevant 

unknowns in FARS in the same proportions as corresponding 

known values.4 Starting with reports based on FARS 2003, 

NCSA will adjust the estimate of lives saved by MLDA laws 

in a similar fashion. First, the proportion of FARS fatalities in 

*John Kindelberger is a mathematical statistician with the Mathematical Analysis Division of the National Center for Statistics and Analysis, NHTSA.
NHTSA’s National Center for Statistics and Analysis 2 400 Seventh St., S.W., Washington, D.C. 20590

crashes involving at least one driver age 18-20, relative to 

all FARS fatalities, will be calculated. Second, this proportion 

will be applied to the number of FARS fatalities in crashes 

involving no known driver of age 18-20 but at least one driver 

of unknown age. Since breaking the allocation into driver 

age groups by number of vehicles can involve sparse counts 

leading to unreliable estimates, the allocation will be done 

over all crash configurations. The adjustment will result in a 

slightly higher estimate than would have been made without 

it. 

Since past lives saved figures have been widely published and 

cited, and the effect of the method update is small, NCSA will 

not recalculate the estimates for past years.

Example

As an example of the old and new methods, the calculation 

of lives saved due to minimum drinking age laws in the year 

2003 is detailed in this section. In the FARS 2003 Annual 

Report file, 5,153 fatal crashes occurred where at least one 

driver of age 18-20 was involved, resulting in 5,923 fatally 

injured persons (of any age). Under the previous method, the 

2003 estimate of lives saved to due to MLDA laws would be:

.13[5,923/(1-.13)] = .13 (6,808) = 885.04 ≈ 885.

Or, equivalently, 6,808 – 5,923 = 885.

However, under the method update, counts of crashes with 

other driver configurations are also involved. The following 

numbers are needed:

• 5,153 fatal crashes occurred where at least one driver of 

age 18-20 was involved, resulting in 5,923 fatalities;

• 32,171 fatal crashes occurred where no driver of age 18-

20 or of unknown age was involved, resulting in 35,741 

fatalities; and

• 928 fatal crashes occurred with no known driver of age 

18-20 but at least one driver of unknown age, resulting in 

979 fatalities.

To take into account the 979 fatalities of unknown category, 

they are allocated according to observed proportions where 

categories are known. In FARS crashes for 2003 of known 

target status, the proportion in the target category is 5,923/

(5,923+35,741)=14.22 percent. This proportion is applied to 

the 979 for an estimate of how many of the 979 were likely in 

crashes of target category:

• Estimated additional fatalities in target group = 

979(5,923/[5,923+35,741]) = 139.18

• Estimated lives lost in target category crashes= 

5,923+139.18 = 6,062.18

If MLDA laws reduce fatalities in targeted crashes by 13 

percent, then without the laws we would expect to have seen 

6,062.18/(1-.13) = 6,968.02 fatalities. Under the update, the 

lives saved estimate will be:

• Estimated number of lives saved due to MLDA laws = 

.13(6,968.02) = 905.84 ≈ 906. 

Equivalently, 6,968.02–6,062.18=905.84 ≈ 906.

Lives Savable

In most lives saved categories, NCSA also produces estimates 

of the numbers of lives that could have been saved if the 

safety measure in question had been applied at higher rates. 

However, the effectiveness rating used in the lives saved by 

MLDA calculation refers not to alcohol consumption but to 

the existence of the law itself1. Since all 50 states have set 

their minimum drinking age at 21, the nation is already fully 

covered by the instrument of effectiveness. Thus estimates of 

lives savable due to increased coverage are not meaningful, 

and NCSA does not publish such estimates.
NHTSA’s National Center for Statistics and Analysis 3 400 Seventh St., S.W., Washington, D.C. 20590

Appendix 

Cumulative Estimated Number of Lives Saved by Minimum Legal Drinking Age Laws, 1975-20021 

References

1. National Center for Statistics and Analysis, Traffic Safety Facts 2002 – Alcohol, NHTSA Fact Sheet, DOT HS 809 606

2. Arnold, R.D., Effect of Raising the Legal Drinking Age on Driver Involvement in Fatal Crashes: The Experience of Thirteen 

States, NHTSA Technical Report, DOT HS 806 902, November 1985

3. Womble, K., The Impact of Minimum Drinking Age Laws on Fatal Crash Involvements: An Update of the NHTSA Analyses, 

NHTSA Technical Report, DOT HS 807 349, January 1989 Revised 

4. Glassbrenner, D., Improving the Calculations of the Lives Saved and Savable by Safety Belts and Air Bags, NHTSA Technical 

Report, DOT HS ......, publication pending 

For additional copies of this research note, please call 800-934-8517 or fax your request to 202-366-3189. For questions 

regarding the data reported in this research, contact John Kindelberger (202-366-3365). This research note and other 

general information on highway traffic safety may be accessed by Internet users at: 

www-nrd.nhtsa.dot.gov/departments/nrd-30/ncsa/AvailInf.html

14,816 15,667 16,513 17,359 18,220 19,121 20,043 20,970 21,887

1975-94 1995 1996 1997 1998 1999 2000 2001 2002
NHTSA’s National Center for Statistics and Analysis 4 400 Seventh St., S.W., Washington, D.C. 20590