Canadian provinces adopting
children's bicycle helmet legislation had a greater average fall in head injury percentages (%HI)
than those with no legislation.1 However, trends unrelated to changes in helmet wearing were
observed in %HI in Australia and New Zealand.2,3 In Australia, the trends were found to vary from state to state, and showed strong correlations with head injury rates of pedestrians.2,4
Whenever possible, %HI for cyclists should therefore be compared to equivalent data for pedestrians.
Another safeguard to help avoid confusing trends with the effect of helmet laws, is to check that changes
in %HI over time are consistent with changes in helmet wearing.
Individual graphs of the two Canadian provinces representing 89% of injuries to child cyclists in
legislation provinces1 are very revealing. For British Columbia (BC), the largest
single-year fall (7.4 percentage points, from 39.9% to 32.5%) was from 94/95 to 95/96. This could not have
been caused by legislation commencing in September 1996 (Fig. 1). A year before legislation (95/96), %HI
was 2.7% less than no-law provinces; a year after legislation (97/98), it was 2.5% less. Far from reducing
%HI, the effect of legislation in BC relative to no-law provinces was therefore a small, but non-significant
increase of 0.2%.
In Ontario, legislation commenced in October 1995.1 Helmet wearing rates and numbers of
cyclists were recorded in Toronto, Ontario's largest city. Only numbers of cyclists counted were
reported,5 not the changes in helmet wearing with the law, which was apparently not
enforced.6 Most cycling in the 95/96 fiscal year would have taken place before legislation,
because freezing Ontario winters are not particularly conducive to cycling. Thus the fall from 94/95 to
95/96 was probably not due to legislation, but an expression of the same trend as BC, noted above to be
unrelated to the law. The main increase in helmet wearing in Ontario, and hence and main effect of
the helmet law, should have been evident in 96/97 data, but this is not apparent from Fig 1. Unless there
is reason to believe that legislation in October 1995 increased wearing rates in 97/98 significantly above
those in 96/97, it seem implausible that the largest fall in %HI (from 33.9% in 96/97 to 28.5% in 97/98)
was actually due to helmet legislation.
Fig. 1 shows that, despite the effect of legislation and slightly fewer bike/motor vehicle crashes in
helmet-law provinces1 (which should result in marginally lower %HI), post-law %HI in Ontario and BC was not significantly different to no-law provinces. The largest differences in %HI were before, not after, the
laws. This strongly suggests that trends, rather than the helmet legislation, may have been responsible
for the changes over time.
Macpherson et al. claimed that the Canadian data, most of which is shown in Fig. 1, show a
"strong protective association between helmet legislation and head injuries".1 The fact that
the largest changes in head injury rates happened either before (in BC), or more than a year after (Ontario)
the start of legislation, and that post law %HI in legislation provinces was not significantly different to
%HI in provinces with no legislation, suggests that this conclusion is highly questionable.
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