Andrea Nucera 1, Alfredo Ruta 2, Laura Marinaro 3 and Maria Chiara Antoniotti 1
1 Suprazonal Epidemiology Service, ASL NO, Novara
2 Epidemiology, ASL CN2, Cuneo
3 Integrated Prevention Department, ASL VC, Vercelli
Road accidents are the main cause of death and disability in the population under 40 years of age and represent a priority health problem in Italy (1). Among the measures aimed at mitigating the consequences, individual safety devices have shown great practical efficacy (2). For this purpose, the Highway Code lays down the obligation to use a helmet for motorcyclists and safety belts for those traveling by car. To monitor compliance with the legislation on the obligation to wear these safety devices and to verify the effectiveness of the policies aimed at promoting their use, it is necessary to reliably measure their current use.
Most commonly, the prevalence of use is measured as a reported habit, through self-filled interviews or questionnaires, or as behavior observed directly on the street. Both methods have advantages and limitations, for example observational studies are more precise but are expensive and based on one-off observations. On the other hand, interview-based studies are economic but may offer a deformed image of reality, because respondents often tend to present their habitual behavior as conforming to prudence and norms, while in reality, it may not be so (3).
Starting from 2007, in the health companies of the Piedmont region, as in most ASLs in Italy, the data reported on the use of safety devices are reported regularly, every year, by the surveillance system Passi (Healthcare Company Progress for Health in Italy) (4), but there are no assessments regarding their validity. Since in Piedmont, during the continuous collection of data carried out by the PASSI system, the use of safety devices in cars and motorcycles was detected, through observation, we were able to compare the results of the two systems, in order to assess the validity of the data reported.
Between April 2007 and March 2008, in the Piedmont region, suitably trained ASL staff conducted the Project "Road Accident Surveillance Activities" (ASIS) detecting, through road observation, the use of individual protection systems for road safety, in particular, "by estimating the proportion of front and rear drivers and passengers who use the seat belt, the proportion of motorcycle drivers who wear helmets and the proportion of children correctly insured by child seats" (5). For this purpose, a protocol has been prepared in which the methods of detection and sampling sites have been defined, specifying the observation points, by type of road, in order to achieve representativeness of the regional road network (5). Gatwick Airport Minicabs Service
In the period June 2007-December 2008, the PASSI surveillance system estimated the habits of the population regarding the use of security systems, by telephone interview on a representative sample of the population aged between 18 and 69, with the aim, between the other, to estimate the reported prevalence of use of the safety devices. To facilitate the comparison between the two data collections, only the responses of people who declared to use the "always" were taken into consideration. The comparison was made on the head obtained from the results obtained by the two detection systems.
The table shows the percentages of use of the security systems at the regional level and the confidence limits. For the use of the front seat belt, the prevalence of habit estimated by PASSI is 13 percentage points higher than the prevalence estimated by direct observation, a statistically significant difference.
For the rear belt, the difference between the reported habit and the observed behavior is 3 percentage points, with overlapping of the confidence intervals and, as regards the use of the helmet, the estimates are both very high and identical.
The results of this study show that, in Piedmont, the PASSI surveillance returns a reliable picture regarding the use of the helmet and the rear belt, while it tends to provide too positive a description of the use of the front belt. In fact, in this case, we are led to believe that 9 out of 10 front travelers wear the belt, while the observed figure is between 7 and 8 out of ten.
This result is not unexpected, because several studies have shown that the prevalences based on self-reported data are generally higher than those drawn from observational data, a fact - generally attributed to a bias of social desirability - so in countries like ours, in where the mandatory legislation is in force, should be corrected by a factor between 1.2 and 1.4 (6).
However, it is necessary to report the limits of the comparison between ASIS and PASSI. First of all, the two surveys reveal different phenomena and the prevalences are calculated with different numerators and denominators, so a rigorous comparison is not possible. In ASIS the behavior adopted by the occupants, even non-residents, of vehicles circulating in the ASL/region territory is studied, while in Passi the habit of drivers/passengers residing in that ASL/region is studied, regardless of where and how much they circulated.
Furthermore, PASSI interviews people between 18 and 69 years of age, therefore it excludes minors who are common users of motorized two-wheelers and older people who also drive and are transported by car.
Finally, in the ASIS study, certain categories of means of transport are excluded from the observation, such as trucks, public transport and police vehicles and carabinieri, whose safety habits are not described, but which may be different from the rest of the sample.
While taking into account these limits, the comparison, in general terms, supports the idea that the data reported on the use of road safety devices can be better interpreted taking into account the results of the more expensive observational studies, carried out at multi-annual intervals. In fact, the advantages of studies based on telephone interviews, such as PASSI, are the regular availability of data at low costs, in addition to the representativeness of the local population and the possibility of studying the individual characteristics associated with non-compliant behaviors. Furthermore, due to the characteristic of the PASSI surveillance of continuously collecting information, it is possible to detect changes in behavior deriving from appropriate information campaigns.
Specifically, it can be concluded that PASSI, in Piedmont, produced in 2007-08 an image practically superimposable to that provided by direct observation, to monitor the use of the motorcycle helmet and the belt for travelers on the rear seats of the auto, while it provided a higher estimate of the use of the front seat belt compared to ASIS. it is necessary to take these values into account when interpreting the data correctly so that they can be used by law enforcement, planners and decision-makers.
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