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Research Note
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DOT HS 809 557 March 2003 |
Safety Belt Use in 2002 � Demographic Characteristics
Safety belt use among African Americans rose to 77%, a
sizable 8-point gain over their use two years ago.� More than a quarter of Blacks who were not using belts in 2000 used
them in 2002.� These results are from
the National Occupant Protection Use Survey (NOPUS), which is the only probability-based
observational survey of safety belt use in the United States.� The survey also found:
�
The belt gender gap appears to be narrowing.�
Males registered a 5-point gain, which reduced the gap from 10 to 7
points.� Males now use belts 72% of the time, while females use 79% of the
time.
�
Belt use has increased dramatically among older children, with
82% of 8-15 year-olds now using belts.
�
Belt use has increased in rural areas.
NOPUS is conducted periodically by the National Center
for Statistics and Analysis (NCSA) in the National Highway Traffic Safety
Administration (NHTSA).� The data in
this note were collected between June 3, 2002 and June 22, 2002, during which
approximately 38,000 drivers and 12,000 passengers were observed at 1,141
randomly selected road sites.� This
note supplements the 2002 NOPUS data reported in [N], which contains results
on belt use by such characteristics as time of day and type of belt enforcement
law.
New
Age Categories in 2002
Prior to 2002, NOPUS had observed�� demographic characteristics (age, race, gender,
and urbanization) for front seat outboard occupants over the age of 4.�
This year, changes instituted to incorporate booster seat use resulted
in restricting the collection of demographic data to those occupants over
the age of 7.� (The age range 4-7 comprises most of the children
who should be in booster seats, and so this group was added as a category
of children in NOPUS.� Results on the
restraint use of these children, as well as children under 4, can be found
in [C].) That is, the NOPUS age groups in this note changed as follows in
2002.
Table 1: Changes in NOPUS Age Groups
Age Group |
Definition in |
|
1994-2000 |
2002 |
|
Youth |
5-15 |
8-15 |
Young Adult |
16-24 |
16-24 |
Adult |
25-69 |
25-69 |
Senior |
70+ |
70+ |
* Donna Glassbrenner is a Mathematical Statistician
in the Mathematical Analysis Division, National Center for Statistics and
Analysis, NHTSA.
Changes in 2002 to Improve Reliability
NOPUS collects demographic information
at intersections that are controlled by a stop sign or stoplight, where stopped
traffic permits the collection of several data items.� In previous years, NOPUS collected this data
at the controlled intersections that were employed by the NOPUS Moving Traffic
Study. [G] In the period 1994-1998, there were approximately 2,000 such controlled
intersection sites, while a reduction in the sample and a definitional change
in 2000 cut these to about 700 (erroneously stated as 1,200 in [D]).� Starting in 2002, demographic data were also
collected at any controlled intersection that the data collectors could find
on the road segment selected in the previous sampling stage of the Moving
Traffic sample for those 1,300 Moving Traffic sites that are not controlled
intersections.� The enlarged demographic
sample remains effectively a probability sample, since the road segments were
selected probabilistically, and only the determination of a controlled intersection
on certain road segments was not probabilistic.� For more information on NOPUS�s sample design,
see [N].
The addition of new sites substantially
improved NOPUS�s demographic estimates.� In
2000, 12,000 vehicles were observed at 700 sites, compared to 38,000 vehicles
at 1,100 sites in 2002, cutting standard errors approximately in half.
Design Aspects Affecting NOPUS Estimates
NOPUS conducts its observations during
daylight hours, during which data collectors observe the shoulder belt use
of drivers and right front passengers in passenger vehicles having no commercial
markings, at intersections that are controlled by a stop sign or stoplight.�
NOPUS includes the first vehicle to stop at the intersection, although
these occupants might tend to have higher levels of restraint use.�
Classifications of age, race, and urbanization are made according to
the best judgment of the data collectors. These protocols may slightly bias
the estimates.� In particular, belt
use might be lower at night and in the rear seat.�
It is not clear what the net effect of misclassifications of age, race,
and urbanization is. However, although controlled intersections tend to exhibit
higher use rates than general road sites (because such intersections are more
common in urban areas), the estimates in this report have been adjusted using
the NOPUS Moving Traffic Study in a manner that reflects use on general roadways.
[N] That is, the data in this note describe belt use in the front outboard
seating positions in passenger vehicles (with no commercial markings) during
daylight hours, on general roadways.
Conversion Rates
The tables in this note give the use
rates, changes in use in 2000-2002, the sampling errors of both of these statistics,
and the conversion rates of the 2000-2002 changes.� The conversion rate is the percentage reduction
in nonuse and represents the percent of nonusers who were �converted� to using
belts in the specified time period. For instance, nonuse among males was reduced
by 15% in 2000-2002, which, for simplicity, the reader might think of as follows:
15% of the males who were not using belts in 2000 were using them in 2002.
African Americans Register a Major Gain
Belt use among Blacks increased 8 percentage
points, from 69% in 2000 to 77% in 2002.� More than a quarter of African Americans who weren�t using belts
in 2000 were using them in 2002.� The
increase among Blacks is statistically significant with 89% confidence.� These improvements are due in substantial part
to efforts by NHTSA�s partners, such as Meharry Medical College and the Blue
Ribbon Panel to Increase Seat Belt Use Among African Americans.
NOPUS has never detected a statistically
significant difference in belt use among the races.� However, the 2002 survey observed many more
minorities than previous surveys (38,000 Whites, 6,000 Blacks, and 5,000 other
individuals), and so was more capable of detecting a difference.
Belt use by members of other racial groups (those not characterized
as White or Black by the data collectors) increased 9 percentage points, to
78% use.� Data collectors are instructed
to categorize occupants who appear to be White Hispanic, Asian American, or
American Indian as members of the Other category. Racial categorizations based
on observation are, of course, susceptible to error, and we cannot estimate
its impact on the belt use estimates.� NOPUS does not observe ethnicity.� It will be interesting to see whether the gains
seen among minorities in NOPUS are born out in the NHTSAs Motor Vehicle Occupant
Safety Survey, whose racial and ethnic data are more reliably obtained through
interviews. [M]
That all racial estimates (White, Black, and Other) exceed
the national estimate of 75% is an artifact of the estimator used by the survey.�
Each excess is within sampling error.�
Although they are mutually inconsistent, the estimates of 75% national
use, 76% white use, 77% black use, and 78% use by other races were obtained
scientifically and are the best estimates available.
The
Gender Gap Might Be Closing
Since its inception in 1994, NOPUS has generally seen a
10-point gap in belt use by males and females, with females consistently found
to use belts more.� In 2002, the disparity
has narrowed to 7 points, with females using belts 79% of the time, compared
to 72% for males.
The narrowing of the gap is due largely to the 5-point
increase in male use, which corresponds to a 15% conversion rate.� We are 86% confident that males used belts
more in 2002 than they did in 2000.� However,
female use continues to be statistically higher than male use.
The lower use by males has substantial consequences.�
The vast majority of the thousands of lives that are lost each year
from not using belts are male. [L] This is partly because males use belts
less and partly because they are on the road more.
Older
Children Are Using Belts More
Belt use increased among older children, from 66% among
5-15 year olds in 2000 to 82% among 8-15 year olds in 2002.� This increase is statistically significant,
and older children saw some of the largest conversion rates in 2002.� However this substantial increase in use might
be due in whole or in part to the change in age range.� In addition, these estimates, and all age estimates,
are influenced by the difficulty of assessing age through observation, and
we cannot measure the extent to which age misclassifications affect the estimates.
Age
Now a Significant Factor in Belt Use
Among its age categories, NOPUS generally sees the lowest
belt use among young adults (16-24), and use generally increases with age
among people 16 and over.� These differences,
however, were previously not statistically significant, perhaps because the
previous surveys did not observe at sufficiently many sites to detect a difference.�
With the enlarged sample used in the 2002 survey, age is now a significant
factor in belt use.� Occupants ages 8-15 and those 70 and over use
belts more than those in 25-69 age range, while 16-24 year olds use belts
less often.
Use
Increases in Rural Areas
Belt use in rural areas increased 5 points, from 68% in
2000 to 73% in 2002.� Belt use was
found to be 72% in urban areas and 76% in suburban areas.
Urbanization is assessed subjectively by the data collectors,
and this may impact the estimates.� In
addition, note that occupants observed in rural areas might or might not live
in a rural area.
NOPUS has consistently found belt use to be statistically similar in urban, rural, and suburban areas.� However, the increased reliability of the 2002 data means that the finding of similarity in 2002 is more likely due to an actual similarity, rather than sampling error.
Characteristic |
Use in 2002 Among Ages 8 and Older |
Use in 2000 Among Ages 5 and Older |
2000-2002
Change |
||||
Estimate* |
Standard Error |
Estimate* |
Standard Error |
Estimate# |
Standard Error |
Conversion Rate |
|
Age 5-15 or 8-15 |
82% (H) |
2.4% |
66% |
7.4% |
16% (S) |
7.8% |
47% |
16-24 |
69% (L) |
1.9% |
69% |
3.5% |
0% |
4.0% |
0% |
25-69 |
76% |
1.7% |
72% |
3.0% |
4% |
3.4% |
14% |
70+ |
82% (H) |
1.9% |
76% |
3.7% |
6% |
4.1% |
25% |
Female |
79% (H) |
1.7% |
77% (H) |
2.6% |
2% |
3.1% |
9% |
Male |
72% |
1.6% |
67% |
3.0% |
5% |
3.4% |
15% |
White |
76% |
1.6% |
74% |
2.9% |
2% |
3.3% |
8% |
Black |
77% |
2.2% |
69% |
4.8% |
8% |
5.3% |
26% |
Other |
78% |
1.9% |
69% |
5.9% |
9% |
6.2% |
29% |
Urban |
72% |
2.0% |
72% |
7.0% |
0% |
7.3% |
-1% |
Suburban |
76% |
2.7% |
72% |
2.9% |
4% |
3.9% |
16% |
Rural |
73% |
2.2% |
68% |
3.7% |
5% |
4.3% |
16% |
*H,L:
significantly high or low use in its category.
Survey
Design
The results in this note were observed during the Controlled
Intersection Study of NOPUS.� This
survey uses a multi-stage probability sample of roadways to ensure reliable
estimates.� The Controlled Intersection
sample consists of intersections that are controlled by a stop sign or a stoplight,
at which stopped and slowed traffic permit detailed observation.�
For a complete description of the sample design, see [N].�
Data collectors observe belt use and demographic characteristics (race,
age, gender) of the drivers and right front passengers of passenger vehicles
during daylight hours between 10 AM and 6 PM. Demographic classifications,
as well as urbanization, are made according to the best determination of the
data collectors.� The results in this
note were obtained at 1,141 sites between June 3, 2002 and June 22, 2002,
at which 38,000 vehicles were observed.� Approximately
22,000 drivers were observed in passenger cars, 10,000 in vans and sport utility
vehicles (SUVs), and 6,000 in pickup trucks.� Likewise, 7,000 passengers were observed in
passenger vehicles, 3,000 in vans and SUVs, and 2,000 in pickup trucks.
The field data is entered, edited, and missing values of
certain variables (race, age, and gender) imputed.� Estimates and sampling errors are computed incorporating the complex
sample design.� Estimates are adjusted
so that the estimates of national belt use in the 2002 Moving Traffic and
Controlled Intersection studies agree.� This
ensures that the Controlled Intersection estimates represent use on general
roadways.� Although we plan to use
direct estimation of variances of differences in future surveys, the variances
on the 2000-2002 differences in this note are based on the assumption that
the 2000 and 2002 surveys are independent.
Assessing
Significance
Because NOPUS uses a probability sample, one can calculate the error its estimates incur from observing use for a sample of roadways and times rather than for all roads and times.� The actual quantity being estimated by a NOPUS estimate is within twice the standard error of the estimated value with 95% confidence.� (Standard errors are provided in the tables in this note.)� This computation can be used to determine whether differences, such as the difference in belt phone use among males and females in passenger cars, are statistically significant.� See [N] for detailed examples of such calculations.
Additional Tables
Table
2: Belt Use by Age and Vehicle Type
Characteristic |
Use in 2002 Among Ages 8 and Older |
Use in 2000 Among Ages 5 and Older |
2000-2002 Change |
||||
Estimate* |
Standard Error |
Estimate* |
Standard Error |
Estimate# |
Standard Error |
Conversion Rate |
|
Age 5-15 or 8-15 |
82% |
2.4% |
66% |
7.4% |
16% (S) |
7.8% |
47% |
Passenger Cars |
82% |
2.6% |
72% |
8.3% |
10% |
8.7% |
36% |
Vans & SUVs |
87% |
2.6% |
75% |
8.8% |
12% |
9.2% |
48% |
Pickup Trucks |
72% |
10.4% |
45% |
12.7% |
27% |
16.4% |
49% |
Age
16-24 |
69% |
1.9% |
69% |
3.5% |
0% |
4.0% |
0% |
Passenger Cars |
69% |
1.8% |
73% |
4.3% |
-4% |
4.7% |
-15% |
Vans & SUVs |
74% |
3.2% |
65% |
5.3% |
9% |
6.2% |
26% |
Pickup Trucks |
63% |
4.2% |
50% |
9.2% |
13% |
10.1% |
26% |
Age
25-69 |
76% |
1.7% |
72% |
3.0% |
4% |
3.4% |
14% |
Passenger Cars |
78% |
1.8% |
74% |
3.0% |
4% |
3.5% |
15% |
Vans & SUVs |
78% |
1.4% |
75% |
4.0% |
3% |
4.3% |
12% |
Pickup Trucks |
64% (L) |
3.1% |
59% (L) |
5.4% |
5% |
6.2% |
12% |
Age
70 and Older |
82% |
1.9% |
76% |
3.7% |
6% |
4.1% |
25% |
Passenger Cars |
82% |
2.0% |
78% |
4.2% |
4% |
4.7% |
18% |
Vans & SUVs |
87% |
2.4% |
76% |
5.7% |
11% |
6.2% |
46% |
Pickup Trucks |
72% (L) |
4.2% |
62% |
11.3% |
10% |
12.1% |
26% |
*H,L: significantly
high or low use in its category.
Table
3: Belt Use by Gender and Vehicle Type
Characteristic |
Use in 2002 Among Ages 8 and Older |
Use in 2000 Among Ages 5 and Older |
2000-2002 Change |
||||
Estimate* |
Standard Error |
Estimate* |
Standard Error |
Estimate# |
Standard Error |
Conversion Rate |
|
Females |
79% |
1.7% |
77% |
2.6% |
2% |
3.1% |
9% |
Passenger Cars |
80% |
1.6% |
76% |
3.0% |
4% |
3.4% |
17% |
Vans & SUVs |
82% |
1.6% |
76% |
5.0% |
6% |
5.3% |
25% |
Pickup Trucks |
71% (L) |
4.5% |
62% |
5.3% |
9% |
6.9% |
24% |
Males |
72% |
1.6% |
67% |
3.0% |
5% |
3.4% |
15% |
Passenger Cars |
74% |
1.9% |
70% |
2.8% |
4% |
3.4% |
13% |
Vans & SUVs |
74% |
1.8% |
71% |
3.3% |
3% |
3.7% |
10% |
Pickup Trucks |
65% (L) |
2.4% |
58% (L) |
5.3% |
7% |
5.8% |
17% |
*H,L: significantly
high or low use in its category.
Table
4: Belt Use by Race and Vehicle Type
Characteristic |
Use in 2002 Among Ages 8 and Older |
Use in 2000 Among Ages 5 and Older |
2000-2002 Change |
||||
Estimate* |
Standard Error |
Estimate* |
Standard Error |
Estimate# |
Standard Error |
Conversion Rate |
|
Whites |
76% |
1.6% |
74% |
2.9% |
2% |
3.3% |
8% |
Passenger Cars |
78% |
1.7% |
77% |
2.9% |
1% |
3.3% |
4% |
Vans & SUVs |
79% |
1.7% |
75% |
2.9% |
4% |
3.3% |
16% |
Pickup Trucks |
66% (L) |
3.0% |
57% (L) |
4.8% |
9% |
5.7% |
21% |
Blacks |
77% |
2.2% |
69% |
4.8% |
8% |
5.3% |
26% |
Passenger Cars |
78% |
2.1% |
68% |
5.2% |
10% |
5.6% |
31% |
Vans & SUVs |
78% |
4.1% |
69% |
6.3% |
9% |
7.5% |
29% |
Pickup Trucks |
68% |
5.8% |
53% |
14.3% |
15% |
15.4% |
32% |
Other
Races |
78% |
1.9% |
69% |
5.9% |
9% |
6.2% |
29% |
Passenger Cars |
79% |
2.1% |
69% |
7.1% |
10% |
7.4% |
32% |
Vans & SUVs |
76% |
4.3% |
78% |
3.9% |
-2% |
5.8% |
-9% |
Pickup Trucks |
74% |
3.0% |
78% |
9.7% |
-4% |
10.2% |
-18% |
*H,L: significantly
high or low use in its category.
Table
5: Belt Use by Urbanization and Vehicle Type
Characteristic |
Use in 2002 Among Ages 8 and Older |
Use in 2000 Among Ages 5 and Older |
2000-2002 Change |
||||
Estimate* |
Standard Error |
Estimate* |
Standard Error |
Estimate# |
Standard Error |
Conversion Rate |
|
Urban |
72% |
2.5% |
72% |
7.0% |
0% |
7.4% |
0% |
Passenger Cars |
72% |
2.6% |
73% |
6.8% |
-1% |
7.3% |
-4% |
Vans & SUVs |
72% |
3.0% |
70% |
7.2% |
2% |
7.8% |
7% |
Pickup Trucks |
69% |
3.8% |
67% |
10.2% |
2% |
10.9% |
6% |
Suburban |
76% |
1.8% |
72% |
2.9% |
4% |
3.4% |
14% |
Passenger Cars |
78% |
2.1% |
74% |
3.1% |
4% |
3.7% |
15% |
Vans & SUVs |
79% |
1.6% |
78% |
2.6% |
1% |
3.1% |
5% |
Pickup Trucks |
69% (L) |
2.7% |
56% (L) |
5.6% |
13% (S) |
6.2% |
30% |
Rural |
73% |
2.2% |
69% |
3.7% |
4% |
4.3% |
13% |
Passenger Cars |
79% |
1.3% |
71% |
5.1% |
8% |
5.3% |
28% |
Vans & SUVs |
78% |
1.8% |
74% |
5.7% |
4% |
6.0% |
15% |
Pickup Trucks |
54% (L) |
6.0% |
55% (L) |
5.2% |
-1% |
7.9% |
-2% |
*H,L: significantly
high or low use in its category.
References
[C] D. Glassbrenner, The Use of Child Restraints in
2002, NHTSA Research Note, DOT HS 809 555, February 2003
[D] N. Bondy and D. Glassbrenner, National Occupant
Protection Use Survey � 2000 Controlled Intersection Study, NHTSA Research
Note, DOT HS 809 318, August 2001
[L] D. Glassbrenner, The Lives Lost by Not Using Safety
Belts, NHTSA Technical Report, to appear
[M] A. Block, 2000 Motor Vehicle Occupant Safety Survey,
Volume 2, Seat Belt Report, NHTSA Technical Report, DOT HS 809 389, November
2001
[N] D. Glassbrenner, Safety Belt and Helmet Use in 2002 � Overall Results,
NHTSA Technical Report, DOT HS 809 500, September 2002
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 Donna Glassbrenner at (202) 366-5358.�
This research� note and other general information on highway
traffic safety may be accessed by internet users at: http://www-nrd.nhtsa.dot.gov/departments/nrd-30/ncsa/AvailInf.html
U.S.
Department
|