1 Epidemic Intelligence Service, Division of Applied Public Health Training, Epidemiology Program Office, Centers for Disease Control and Prevention, Atlanta, GA.
2 Division of Unintentional Injury Prevention, National Center for Injury Prevention and Control, Centers for Disease Control and Prevention, Atlanta, GA.
3 Division of Emergency Medical Services, Florida Department of Health, Tallahassee, FL.
4 Office of Statistics and Programming, National Center for Injury Prevention and Control, Centers for Disease Control and Prevention, Atlanta, GA.
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ABSTRACT |
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bicycling; child; craniocerebral trauma; head protective devices; legislation; safety
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INTRODUCTION |
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Bicycle helmets prevent up to 85 percent of head injuries and 88 percent of serious brain injuries (4, 5
). For every bicycle helmet sold, an estimated $395 is saved in direct medical costs and other costs (6
). Despite such demonstrated effectiveness, a 1994 survey reported that only about half of US children owned a bicycle helmet, and only 25 percent wore one every time or nearly every time they rode (1
). Helmet-use legislation can be an important and effective part of a multifaceted bicycle helmet-use program for children (5
). Since 1987, 18 states, the District of Columbia, and more than 80 cities have enacted such laws or ordinances, covering approximately 49 percent of US children younger than age 15 years. Laws will take effect in two other states by March 1, 2002 (7
).
Evidence of the effectiveness of such laws has been based on studies that used either observational methods (for local studies) or telephone surveys (for statewide surveys). The sentinel study using observational methods was conducted in Howard County, Maryland, in 1990. It showed one of the most impressive increases in helmet use following adoption of a law to date: from 4 percent to 47 percent (8). Although observational studies are considered preferable to telephone surveys, they are relatively resource-intensive and thus have been applied only to local or county jurisdictions. Local findings may not be generalizable to larger populations, because of the relative socioeconomic homogeneity of a single county. Statewide surveys would be more representative of the entire national population.
Two statewide surveys have been conducted by telephone. In Georgia, proxy-reported helmet use increased from 37 percent to 66 percent following the adoption of a state law (9). In Oregon, proxy use reported by telephone increased from 37 percent to 67 percent (10
), although observations at 13 sites indicated that helmet use was 25 percent before the law took effect and 49 percent afterwards. Stronger evidence based on observational studies conducted statewide is needed to help reconcile such differences.
With statewide observational methods, one of the fundamental barriers to accurate ascertainment of population-based helmet use is the determination of the sampling frame. Because populations of riders from different geographic areas are likely to differ in their exposure to traffic, trip duration, and pattern of helmet use, developing a probability sample based on exposure to bicycle-riding is challenging, if not impossible. A new look at study design was needed to overcome this limitation. Accordingly, we sought a site in which to survey all elementary schools across a state, rather than sample a supposedly representative population of riders.
Florida is an excellent site at which to study the effectiveness of a state law mandating use of bicycle helmets. Its warm climate affords year-round bicycling and thus relatively high exposure. It also has one of the highest numbers of children killed while bicycling in the nation. On the basis of a four-county 1991 study that indicated 15 percent helmet use, baseline helmet use in Florida appeared to be low, despite the implementation of a multifaceted intervention program (11).
On January 1, 1997, a state law (Florida Statutes 1996, Title XXIII, Chapter 316.2065) took effect mandating that all bicycle riders younger than age 16 years wear a helmet while riding (12). In the first year, law enforcement officers were authorized to issue verbal warnings and bicycle safety brochures to violators. After January 1, 1998, officials could issue a citation that carried a $15 fine. A provision to "opt out" of the state law provided a natural experiment in which to estimate its effectiveness. The law included a provision allowing a county to exempt itself from the legislation if its board of county commissioners, after holding a public hearing, passed an exemption ordinance before January 1, 1998 (12
). Three counties (Brevard, Citrus, and St. Lucie counties), each with 112,000640,000 residents, executed this provision to "opt out" of the law.
Prior to this study, the effectiveness of the law was estimated by other investigators using two different methods. First, direct observations were conducted in one jurisdiction, Duval County, which includes Jacksonville. There, in addition to the law, the intervention included helmet-use education and helmet distribution. Helmet use increased from 13 percent 1 year before the law took effect to 73 percent 16 months after it took effect (13). Second, a statewide telephone survey conducted in 1997 indicated, by proxy report, that about 47 percent of children always wore a helmet while riding a bicycle (14
).
The present observational study was conducted for two reasons. First, we wished to determine the generalizability of the high prevalence of helmet use noted in Duval County. Second, the Florida Department of Health needed school-specific data in order to know where to target its public health prevention efforts.
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MATERIALS AND METHODS |
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After reviewing the survey instructions, school officials (usually the school principal, but sometimes a physical education teacher, school nurse, drug-abuse resistance education officer, or other school staff member) conducted unobtrusive observations of bicycle helmet use by students during 1 day of a 4-month period in spring 1999. A cross-sectional, static-group comparison design was selected because of resource limitations. They recorded helmet use once for each student, either while the student rode up to the bicycle rack at school in the morning or while he/she rode away from it in the afternoon. No attempt was made to identify whether helmets were being worn correctly. The gender and race (White, Black, other) of each child were recorded, but no attempt was made to identify Hispanic ethnicity because of concern about misclassification.
Statistical analyses
The possibility that within-school clustering might influence the results was tested using SUDAAN software (15), with the school district analyzed as the primary sampling unit. The resulting design effect was less than unity, indicating that variances calculated under a simple random-sample assumption using SAS software were larger (and thus more conservative) than those produced by cluster analysis. Thus, the unit of analysis was the observed rider, not the school. Statistical significance for the analysis was tested using Pearson's
2 test, with p values less than 0.05 being considered statistically significant. In addition, we present crude and adjusted prevalence ratios for gender and race obtained by means of Cochran-Mantel-Haenszel statistics.
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RESULTS |
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The demographic profile of children residing in the 50 counties with a helmet-use law was compared with that of children residing in the three counties exempt from the law (table 1). There was no difference in gender distribution between the two types of counties. However, the racial distribution differed between children from counties with a helmet-use law and those from counties without one (p = 0.001). Measures of socioeconomic status were similar between the two types of counties.
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DISCUSSION |
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We considered whether restricting site selection to public school property had biased our results. We chose to observe children only at school sites because we wanted to maximize the number of elementary school children surveyed statewide. Furthermore, the time periods before and after school hours are particularly important to consider, because they are relatively hazardous; approximately 30 percent of all bicycle crashes among children occur while the child is riding to or from school (16). We chose to conduct observational surveys rather than rely on telephone, mail, or classroom surveys, because observations are generally acknowledged to be more accurate and conservative than other survey methods (17
). Measuring helmet use on school property enhanced survey efficiency tremendously by enabling the task to be completed by only one adult observer at the place of work in a short period of time. The school-based method used here also virtually eliminated the possibility of double-counting the same child, a key threat to validity in observational surveys (17
).
One key limitation of this study was our inability to control for the existence of school policies requiring bicycle riders to wear a helmet when riding to and from school. Some Florida schools had already adopted a policy requiring children to wear a helmet while bicycling to school lest they not be allowed to ride their bicycle home that day. If so, our choice to restrict observations to school sites may have produced a spurious association between the existence of a state law and helmet use. A school policy might be expected to increase helmet use among children riding to or from school but not affect helmet use at other times and places. We attempted to quantify this potential bias but could only ascertain the necessary information about the existence of a school policy for approximately one third of schoolstoo few to permit analysis. Meanwhile, we hypothesize that the coexistence of a law and a school policy might be synergistic. Indeed, a state law might be a necessary antecedent to a school policy, empowering reluctant school officials to adopt one. The specific influence of a school policy deserves further study.
Another key limitation of this study was imposed by its cross-sectional, observational design. Because the survey was conducted only once, we could not evaluate any change in helmet use associated with passage of the law or thereafter. The unobtrusive nature of the study prevented us from collecting data on age and other important rider variables. In addition, we made no attempt to measure any joint effectiveness of local bicycle-helmet giveaway and/or educational programs, which in Australia were demonstrated to increase helmet use in advance of a law (18). However, early experience in Duval County suggested that the law had a greater effect than helmet distribution or education (13
). Furthermore, when a helmet giveaway and educational program were provided to all elementary school children in two Texas towns where no helmet-use law existed, change in helmet use was relatively small and unsustained (19
).
We conclude that bicycle helmet-use laws can be powerful stimulants for behavioral change (9). This study showed that helmet use was twice as high in Florida counties where a law was enacted as in counties that opted out of the law. These data support the Healthy People 2010 objective recommending that all 50 states adopt a bicycle helmet-use law for children (20
) in order to increase helmet use and consequently reduce traumatic brain injury.
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ACKNOWLEDGMENTS |
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NOTES |
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REFERENCES |
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