eine "kurze" Zusammenfassung von Studien die den Vorteil des Tragens von Fahrradhelmen zeigen, findet ihr hier:
Case control studies
Most of the evidence in favour of helmet effectiveness has come from 'case control studies' where a group of cyclists with head injuries is compared with one or more groups without.
Case-control studies are less reliable than randomized controlled studies or cohort studies; there are several examples where case-control studies produced incorrect and totally misleading results. Some studies attempt to match ‘cases’ (subjects with head injury) to non-head injured 'controls' with the same age and background. However, as was the case in the first case-control study of helmet wearing (Thompson, Rivara and Thompson, 1989), it is not always possible to find suitable controls. In other studies, researchers attempt to statistically ‘adjust’ for differences such as age or motor vehicle involvement (known as confounders) between cases and controls. Again this can be very difficult to do. For example, helmet wearers tend to be more safety conscious and there is evidence that they have lower impact collisions (Spaite et al, 1991). Case-control studies have not tried to measure safety consciousness or impact speed, so it would be very difficult to fully adjust for them
Randomized controlled trials have not been used in helmet research for practical reasons. Since injuries to cyclists are rare, the researchers would have to find a very large number of participants and persuade some, chosen at random, to wear helmets, others not. The researchers would then have to follow up these people and find out what injuries, if any, they might have had. This would be extremely time-consuming and difficult, and almost all of the participants would have no relevant injury at all.
The Medical Research Library of Brooklyn provides these explanations of medical research methods:
Randomized controlled studies
Case-control studies
Cohort studies
The likelihood of a crash when cycling is not the same for all cyclists or in all situations, and not all crashes are equally likely to result in a head injury. For example, the risk of a crash is very much influenced by social factors (Grayling et al, 2002), cycling skill, where the person is riding and even personal temperament. Serious head injuries are much less likely in crashes with no motor vehicle involved and when a person rides more cautiously. When people choose whether or not to wear a cycle helmet, that too may be influenced by their attitude to and perception of risk and other personal factors. It is probably not possible to compensate for all these variables when comparing groups of cyclists.
Just as gloves prevent minor wounds to the hands, cycle helmets are likely to prevent similar wounds to the head, but these are not serious injuries or in any way life-threatening. In the largest case-control study, 73% of head injuries did not involve concussion or other brain injury (Thompson, Rivara and Thompson, 1996). Based on this wide definition, including all wounds to the head, helmet wearers will have lower rates of head injury. However, the case-control study evidence for other types of head injury is not as consistent as is often suggested. Although one frequently cited but much-criticised study claims that helmets reduce head injuries by 85%, all other studies predict more modest benefits, such as 39% (McDermott, Lane, Brazenore and Debney, 1993) or none at all (for some types of cyclists, e.g. cyclists over 15 riding on-road) (Jacobson, Blizzard and Dwyer, 1998).
Some studies have found that only hard shell helmets protect from head injury (Hansen, Engesaeter and Viste, 2003), or that non-approved helmets offer no benefit (McDermott, Lane, Brazenore and Debney, 1993). It is difficult to see why non-approved and soft shell helmets should offer no benefit at all if protection from hard shell helmets is significant. In today's fashion-conscious market, most helmets on sale have only a thin microshell if any at all, and hard shell helmets are difficult to buy. Moreover, the estimates of protection given by hard shell helmets are very variable. In a single study, odds ratios of 1.2, 0.9 and 0.42 were calculated (##219'#). Other case-control studies also have wide confidence intervals, e.g. 1.16 to 9.06 (Maimaris, Summers, Browning and Palmer, 1994). This makes it very difficult to determine if they show that helmets have any real benefit at all.
Sometimes helmets have been found to protect from injuries to the whole face (Wasserman and Buccini, 1990), sometimes to offer no protection against facial injuries (Hansen, Engesaeter and Viste, 2003) and, in one study, children under 9 who wore foam helmets had four times as many face injuries as non-wearers (Hansen, Engesaeter and Viste, 2003). Claims have been made that helmets can protect from death (Dorsch, Woodward and Somers, 1987), that they are less effective in greater impact crashes (McDermott, Lane, Brazenore and Debney, 1993) and that they only protect against serious, but not more minor, injury (Shafi et al, 1998) which seems improbable. Most of the more serious injuries to cyclists are as a result of a collision with a motor vehicle, but case-control studies have sometimes found helmets to be ineffective in these circumstances (Larsen, 2002).
Some studies have noted how bareheaded riders not only suffer more head injuries, but also more serious non-head injuries in crashes with motor vehicles, suggesting that riding style and other factors may be more important determinants of head injury than whether or not a helmet is worn (Spaite et al, 1991). On the other hand, helmeted cyclists have sometimes been found to have more serious non-head injuries, such as injuries to the neck, the trunk, extremities and pelvic girdle (McDermott, Lane, Brazenore and Debney, 1993; Wasserman and Buccini, 1990; Maimaris, Summers, Browning and Palmer, 1994). It has been suggested that helmeted cyclists hit their heads more frequently than those without helmets (Wasserman et al, 1988).
Significantly, only studies by one team of researchers have concluded that all types of cycle helmet offer protection to all cyclists under virtually all circumstances, with and without motor vehicle involvement (Thompson, Rivara and Thompson, 1989; Thompson, Rivara and Thompson, 1996). It is this research that is most frequently cited in favour of cycle helmet effectiveness and helmet laws.
Scientific research usually takes pains to investigate discrepancies between its own conclusions, those of other research and data from other sources. As a result there is normally much closer agreement about the interpretation of studies than is to be found in cycle helmet research. The positive results from case-control studies may simply result from inability to compensate sufficiently for the many auxiliary differences between helmet wearers and non-wearers.
Most case-control studies on cycle helmets have been the subject of peer criticism and critical meta-analysis (e.g. Towner et al, 2002) for shortcomings that make their conclusions unreliable. For example, there has sometimes been no distinction between head and facial injuries or between life-threatening and minor injuries; data has been self-reported with no checks for reliability; and target groups have sometimes been atypical (e.g. club cyclists). The wider circumstances of crashes have never been taken into account.
Cycle helmet research is not alone in being controversial. In recent years an increasing number of papers in epidemiological journals have drawn attention to the unreliability of findings in case-control studies (BHRF, 1134).
Meta analyses
Three literature reviews of the medical evidence about cycle helmets have been published (Towner et al, 2002; Thompson, Rivara and Thompson, 2002-9; Attewell, Glase and McFadden, 2001). Based almost exclusively on case-control studies, two focus on the same set of studies and the third on a subset of this set. One review (Thompson, Rivara and Thompson, 2002-9) has been criticised for a lack of independence, being dominated by the authors' own studies. Another (Towner et al, 2002) because its conclusion (in favour of cycle helmet effectiveness) is at odds with the extensive criticisms of the studies published in a technical annex.
"A helmet saved my life!"
Powerful evidence for helmet effectiveness comes from the experiences of helmeted cyclists who have hit their heads in a crash and believe that their helmet has saved them from injury. However, there is no evidence that helmets save lives or prevent serious injury at all across cyclists as a whole.
For a full discussion of this paradox, see "A helmet saved my life!".
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