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U.S. Department hitpi//www.nhtsa.dot.zov
of Transportation
aoa hay Research Note
Administration

December 1996

Revised Estimates of Child Restraint Effectiveness

SUMMARY

NHTSA’s National Center for Statistics and
Analysis (NCSA) recently completed an
analysis of data from the Fatal Accident
Reporting System (FARS) to reexamine the
effectiveness of restraints in saving the lives
of children, ages 0 - 4. This analysis
provides updated estimates of the
effectiveness of child restraints for infants
less than 1 year of age and for children 1-4
years of age. Effectiveness estimates were
calculated separately for child restraints used
in passenger cars (PCs) and in light trucks
and vans (LTVs).

METHODOLOGY

This analysis updates the work published in
Lives Saved by Child Restraints from 1982
through 1987 by Susan C. Partyka (DOT HS
807 371, December 1988). Data from FARS
for the period 1988 - 1994 for children
involved in fatal crashes were used in the
current analysis.

The first step in the analysis was selecting
from FARS those fatal crashes involving PCs
and LTVs for which the driver’s and child’s
restraint use and the child’s seating position
were known. For each driver restraint status
(in use or not in use) and each child seating
position (front or rear), two ratios were
compared. The first ratio, the numerator,
was the number of fatalities among infants in
child restraints, divided by the number of
fatalities among their drivers. The second
ratio, the denominator, was the number of
fatalities among unrestrained infants divided

by the number of fatalities among their
drivers. The ratio of these ratios is called a
paired comparison. This resulted in four
paired comparisons, one for each
combination of driver restraint status and
child seating position. To determine relative
tisk of fatality for a restrained infant as
compared to an infant who was unrestrained,
the logarithms of the paired comparisons
were calculated along with their variances
and combined using the methodology
described in Statistical Methods for Rates
and Proportions by Joseph Fleiss (John
Wiley and Sons, 1981). These combined log
risk ratios control for the child’s seating
position and the driver’s belt use. The
combined estimates, along with the standard
errors of the estimates, were used to
construct confidence intervals for the relative
risk. Estimates of restraint effectiveness
were obtained using:

Effectiveness = 1 - exp[log (relative risk))

This resulted in an effectiveness estimate for
child restraints for infants. The same method
was use to calculate child restraint
effectiveness for older children and
effectiveness of adult safety belts for older
children.

RESULTS

Table 1 presents the estimates of the fatality-
reducing effectiveness of child restraints for
PCs and LTVs. All estimates shown in
Table 1 were found to be statistically
significant (a < .05).

National Center for Statistics & Analysis - Research & Development - 400 Seventh St. SW - Washington, DC 20590


Table 1
Estimated Fatality Reducing Effectiveness
of Child Restraints

Age Group ‘|
Vehicle Type
Less than 1 1-4
Passenger N% 54%
Cars
Light Trucks 58% 59%
and Vans |

Adult seat belts were found to be 47%
effective in PCs and 48% effective in LTVs
for children aged 1-4.

In addition, it is estimated that children are
26% less likely to be fatally injured if seated
in the rear of a passenger vehicle. This
estimate was obtained by controlling for
driver and child restraint use and was also
found to be statistically significant

(a <.05).

Using data from 1982 through 1987, Partyka
[1988] found that child safety seats were
69% effective against fatalities for infants
and 47% effective for children aged 1-4. The
present estimates based on data from 1988-
94 for child restraint effectiveness appear to
be consistent with the estimates reported in
Partyka [1988]. In view of the increasing
popularity of LTVs as family vehicles,
separate estimates were calculated for LT Vs.
NHTSA plans to use these revised estimates
for calculating the number of children’s lives
saved. These revised estimates will be
reported beginning in 1997 using data for
calendar year 1996.

Partyka [1988] found adult seat belts to be
36% effective for children. These revised
estimates of adult seat belts (47% for PCs
and 48% for LTVs) are substantially greater.
It is not clear what factors may affect such
an increase in adult belt effectiveness for
children. One possible factor influencing the
increase: as more states have enacted

mandatory belt use laws, a possible bias in
reporting belt use may be present, thereby
distorting estimates of adult belt
effectiveness for passengers of all ages. (For
more information on this, see Report to
Congress on Benefits of Safety Belts and
Motorcycle Helmets, Based on Data from
the Crash Outcome Data Evaluation System
(CODES) by Johnson, Sandra W. and
Walker, Jonathan (DOT HS 808 347,
February 1996) and The Crash Outcome
Evaluation System (CODES) (DOT HS 808
338, January 1996).

Based upon this analysis, the maximum
potential for reducing the risk of fatality for
children occupying passenger vehicles is
obtained by having the child restrained in a
child restraint located in the rear seating
position of the vehicle.

For more information regarding the
methodology used in this analysis or
questions regarding the findings, please
contact Ellen Hertz, Ph.D. of NCSA, at
(202) 366-5360. For additional copies of
this research note, please contact NCSA at
(202) 366-4198 or fax (202) 366-7078.
This research note and other general
information on highway traffic safety may be
accessed by Internet users at
http://www.nhtsa.dot.gov/people/ncsa.

To ensure that your children ride safely,

remember these rules:

e The back seat is the safest place for
children of any age to ride.

e Make sure all infants and children
are properly restrained in child
safety seats or lap and shoulder
belts for every trip.

e Infants riding in rear-facing child
safety seats should never be placed
in the front seat of a vehicle with a
passenger-side air bag.

National Center for Statistics & Analysis - Research & Development - 400 Seventh St. SW - Washington, DC 20590