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Cycle helmets and the law

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Leonard Evans
Leonard Evans
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Abstract

Any discussions of the law and the use of bicycle helmets will be helped by focusing on three questions. Firstly, how much do cycle helmets affect the risk of injury in a crash? Secondly, how much do laws requiring cyclists to wear helmets affect casualties? And, thirdly, should wearing of bicycle helmets be required by law? Answers to the first two questions have objective answers that can be sought from specific empirical studies and what is already known about traffic safety.1 Three unrelated sources of evidence consistently show that cycle helmets reduce risk substantially in a crash. The science of biomechanics shows that a helmet reduces the peak acceleration forces that are associated with injury. Many published epidemiological studies, including that by Maimaris and colleagues in this issue of the BMJ and the references it cites,2 find that helmets reduce injury and the risk of death. Such studies fall short of the methodological ideal of comparing harm in matched treatment and control populations - so less direct methods must necessarily be used. For example, examining the ratio of head injuries to nonhead injuries in cyclists wearing and not wearing helmets indicates that helmets reduce the risk of head injury …
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is
still
widely
used
in
some
countries
to
control
mosquitoes.
Temporal
trends
in
breast
cancer
rates
are
difficult
to
relate
to
changes
in
exposure
to
suspected
risk
factors
because
the
rates
are
affected
by
complex
variations
in
the
known
risk
factors
for
breast
cancer
such
as
age
at
menarche,
age
at
first
birth,
parity,
and
age
at
menopause.
In
several
developed
countries,
however,
breast
cancer
mortality
rates
were
high
before
any
widespread
exposure
to
DDT
or
polychlorinated
biphenyls,
and
the
rates
have
not
risen
strikingly
since
these
chemicals
were
introduced.
The
International
Agency
for
Research
on
Cancer
has
classified
DDT
as
"possibly
carcinogenic"
to
humans,
largely
because
it
can
cause
liver
cancer
in
experiments
on
animals.8
Another
reason
for
suggesting
that
DDT
from
the
environ-
ment
might
cause
breast
cancer
is
that
DDT
is
oestrogenic.
This
is
a
very
theoretical
risk;
even
in
large
doses
DDT
is
only
weakly
oestrogenic
in
animals,
and
it
has
not
been
shown
to
have
oestrogenic
effects
in
women.
Oestrogen
replacement
therapy,
which
has
clear
oestrogenic
effects,
may
increase
the
risk
of
breast
cancer
by
about
30%
after
15
years
of
use,9
so
any
small
oestrogenic
effect
of
DDT
in
the
environment
would
probably
be
impossible
to
detect
by
epidemiological
studies.
Polychlorinated
biphenyls
have
been
classified
by
the
International
Agency
for
Research
on
Cancer
as
"probably
carcinogenic"
to
humans,
with
a
possible
association
with
cancers
of
the
liver
and
biliary
passages.10
Polychlorinated
biphenyls
are
sometimes
referred
to
as
oestrogenic,
but
in
fact
some
show
antioestrogenic
activity,
and
no
oestrogenic
effects
of
polychlorinated
biphenyls
have
been
established
in
women.
112
There
is,
therefore,
no
strong
reason
to
expect
polychlorinated
biphenyls
to
cause
breast
cancer
rather
than
any
other
cancer.
Putting
all
this
evidence
together,
we
conclude
that
it
is
unlikely
that
DDT
in
the
environment
increases
the
risk
of
breast
cancer.
However,
all
published
epidemiological
evidence
comes
from
the
six
studies
cited-based
on
only
301
women
with
breast
cancer
and
412
women
without.
The
question
is
so
important
that
it
seems
justified
to
examine
it
further
in
at
least
the
same
number
of
women
again,
using
specimens
collected
before
the
women
develop
breast
cancer.
For
polychlorinated
biphenyls
there
is
no
evidence
for
an
association
with
breast
cancer
risk,
and
there
seems
to
be
no
need
to
pursue
this
question
further.
TIMOTHY
KEY
Research
scientist
GILLIAN
REEVES
Statistician
Imperial
Cancer
Research
Fund
Cancer
Epidemiology
Unit,
University
of
Oxford,
The
Radcliffe
Infirmary,
Oxford
OX2
6HE
1
Unger
M,
Kiaer
H,
Blichert-Toft
M,
Olsen
J,
Clausen
J.
Organochlorine
compounds
in
human
breast
fat
from
deceased
with
and
without
breast
cancer
and
in
a
biopsy
material
from
newly
diagnosed
patients
undergoing
breast
surgery.
Environ
Res
1984;34:24-8.
2
Mussala-Rauhamaa
H,
Hasanen
E,
Pyysalo
H,
Antervo
K,
Kauppila
R,
Pantzar
P.
Occurrence
of
,-hexachlorocyclohexane
in
breast
cancer
patients.
Cancer
1990;66:2125-8.
3
Falck
FY,
Ricci
A
Jr,
Wolff
MS,
Godbold
J,
Deckers
J.
Pesticides
and
polychlorinated
biphenyl
residues
in
human
breast
lipids
and
their
relation
to
breast
cancer.
Arch
Environ
Health
1992;47:143-6.
4
Wolff
MS,
Toniolo
P,
Lee
E,
Rivera
M,
Dubin
N.
Blood
levels
of
organochlorine
residues
and
risk
of
breast
cancer.7
JNatl
Cancer
Inst
1993;85:648-52.
5
Dewailly
E,
Dodin
S,
Verreault
R,
Ayotte
P,
Sauv
L,
Morin
J,
et
al.
High
organochlorine
body
burden
in
women
with
estrogen
receptor-positive
breast
cancer.
Y
Natl
Cancer
Inst
1994;86:
232-4.
6
Krieger
N,
Wolff
MS,
Hiatt
RA,
Rivera
M,
Vogelman
J,
Orentreich
N.
Breast
cancer
and
serum
organochlorines:
a
prospective
study
among
white,
black
and
Asian
women.
J
Natl
Cancer
Inst
1994;86:589-99.
7
Kutz
FW,
Wood
PH,
Bottimore
DP.
Organochlorine
pesticides
and
polychlorinated
biphenyls
in
human
adipose
tissue.
Rev
Environ
Contam
Toxicol
1991;120:1-82.
8
IARC
monographs
on
the
evaluation
of
carcinogenic
risks
to
humans.
Vol
53.
Occupational
exposures
in
insecticide
application,
and
some
pesticides.
Lyons:
International
Agency
for
Research
on
Cancer,
1991.
9
Steinberg
KK,
Thacker
SB,
Smith
SJ,
Stroup
DF,
Zack
MM,
Flanders
WD,
et
al.
A
meta-analysis
of
the
effect
of
estrogen
replacement
therapy
on
the
risk
of
breast
cancer.
.AMA
1985;265:
1985-90.
10
IARC
monographs
on
the
evaluation
of
carcinogenic
risks
to
humans.
Supplement
7.
Overall
evaluations
of
carcinogenicity:
an
updating
of
IARC
monographs
volunmes
I
to'
42.
Lyons:
International
Agency
for
Research
on
Cancer,
1987.
11
Davis
DL,
Bradlow
HL,
Wolff
MS,
Woodruff
T,
Hoel
DG,
Anton-Culver
H.
Medical
hypothesis:
xeno-estrogens
as
preventable
causes
of
breast
cancer.
Environ
Health
Perspect
1993;101:372-7.
12
Krishnan
V,
Safe
S.
Polychlorinated
biphenyls
(PCBs),
dibenzo-p-dioxins
(PCDDs),
and
dibenzofurans
(PCDFs)
as
antiestrogens
in
MCF-7
human
breast
cancer
cells:
quantitative
structure-activity
relationships.
ToxicolAppl
Pharmacol
1993;120:55-61.
Cycle
helmets
and
the
law
Even
when
the
science
is
clear
policy
decisions
may
still
be
difficult
Any
discussions
of
the
law
and
the
use
of
bicycle
helmets
will
be
helped
by
focusing
on
three
questions.
Firstly,
how
much
do
cycle
helmets
affect
the
risk
of
injury
in
a
crash?
Secondly,
how
much
do
laws
requiring
cyclists
to
wear
helmets
affect
casualties?
And,
thirdly,
should
wearing
of
bicycle
helmets
be
required
by
law?
Answers
to
the
first
two
questions
have
objective
answers
that
can
be
sought
from
specific
empirical
studies
and
what
is
already
known
about
traffic
safety.'
Three
unrelated
sources
of
evidence
consistently
show
that
cycle
helmets
reduce
risk
substantially
in
a
crash.
The
science
of
biomechanics
shows
that a
helmet
reduces
the
peak
acceleration
forces
that
are
associated
with
injury.
Many
published
epidemiological
studies,
including
that
by
Maimaris
and
colleagues
in
this
issue
of
the
BMJ
and
the
references
it
cites,2
find that
helmets
reduce
injury
and
the
risk
of
death.
Such
studies
fall
short
of
the
methodological
ideal
of
comparing
harm
in
matched
treatment
and
control
populations-so
less
direct
methods
must
necessarily
be
used.
For
example,
examining
the
ratio
of
head
injuries
to
non-
head
injuries
in
cyclists
wearing
and
not
wearing
helmets
indicates
that
helmets
reduce
the
risk
of
head
injury
by
more
than
half.
One
important
way
in
which
these
studies
fall
short
of
the
ideal
is
due
to
selective
recruitment,'
3the
tendency
of
people
who
wear
protection
devices
to
differ
in
many
ways
from
those
who
do
not.
Estimates
of
effectiveness
will
be
biased
if
they
ignore
the
reasonable
expectation
that
crashes
will
be
more
severe
for
cyclists
who
do
not
wear
helmets
than
for
those
who
do."
3
The
third
source
of
evidence
is
the
analogy
with
motorcycle
helmets.
The
effectiveness
of
a
motorcycle
helmet
has
been
determined
by
comparing
outcomes
for
a
driver
and
a
passenger
riding
the
same
motorcycle,
and
thereby
having
the
same
crash,
but
one
wearing
and
the
other
not
wearing
a
helmet.'4
The
large
sample
sizes
available
in
data
from
the
United
States
gave
a
precise
estimate
of
the
effectiveness
in
reducing
death
of
28%
(SE
8%).
Similar
effectiveness
was
found
for
drivers
and
passengers
and
for
men
and
women.
Independent
examination
of
the
ratio
of
head
to
non-head
injuries
provides
results
comparable
to
those
in
pedal
cyclists-suggesting
similar
effectiveness
for
bicycle
and
motorcycle
helmets.
A
universal
property
of
all
protection
devices
is
that
effectiveness
declines
as
severity
increases,'
3so
bicycle
helmets
are
less
effective
for
the
higher
severities
that
result
from
crashes
with
other
vehicles.
Even
if
cycle
helmets
protect
in
a
crash
casualties
need
not
necessarily
decline
if
more
cyclists
use
them.
There
is
BMJ
voLuME
308
1
1
JUNE
1994
1521
abundant
evidence
that
human
behaviour
can
reduce,
negate,
or
even
invert
the
expected
outcomes
of
changes
in
traffic
systems.'
The
mass
of
evidence,
mainly
from
laws
governing
the
use
of
safety
belts
in
cars,
shows
that
any
change
in
risk
taking
by
drivers
is
small
and
there
is
more
likely
to
be
a
reduction
in
risk
if
wearing
seat
belts
is
mandatory.'
For
laws
on
cycle
helmets
the
evidence
is
difficult
to
interpret
because
of
small
sample
sizes
and
the
absence
of
the
sudden
increases
in
rate
of
use
generated
by
some
belt
wearing
laws.
One
good
evaluation
found
reductions
in
casualties
associated
with
the
law
in
Victoria,
Australia.'
Although
an
ideal
evaluation
has
not
been
possible
for
laws
on
cycle
helmets,
an
event
in
the
United
States
provided
a
unique
opportunity
to evaluate
a
law
on
motorcycle
helmets.
Under
pressure
from
the
federal
government
nearly
all
50
states
passed
laws
making
motor-
cycle
helmets
mandatory
in
the
mid-1
960s.
Congress
removed
that
pressure
in
1976,
and
soon
after
about
half
of
the
states
repealed
their
laws.
This
made
possible
a
near
optimum
natural
experiment,
the
results
of
which
showed
that
repeal
led
to
a
25%
(4%)
increase
in
deaths
of
motorcyclists.'
This
effect
is,
if
anything,
larger
than
expected,
thus
ruling
out
the
possibility
that
wearing
helmets
leads
to
any
large
increase
in
risk
taking.
Laws
on
wearing
motorcycle
helmets
had
the
expected
effect,
and
it
seems
hard
to
imagine
plausible
reasons
why
the
case
for
cycle
helmets
would
be
all
that
different.
The
evidence
is
fairly
compelling
that
passing
a
law
making
the
wearing
of
cycle
helmets
mandatory
will
result
in
appreciable
reductions
in
casualties.
Accepting
that
a
law
would
reduce
casualties
does
not
inexorably
require
that
such
laws
ought
to
be
passed.
Many
unappealing
laws
could
reduce
traffic
casualties.
Successfully
prohibiting
passengers
from
travelling
in
front
seats
of
cars
while
any
rear
seat
remained
unoccupied
would
prevent
many
casualties
because
of
the
substantially
lower
risk
in
rear
seats.'
The
advantages
of
social
interaction
and
a
better
view
make
it
unlikely
that
any
such
law
will
find
support.
Being
compelled
to
wear
a
bicycle
helmet
does
not
incur
such
large
negatives,
but
it
does
require
a
diminution
in
freedom.
No
scientific
investigation
can
ever
lead
to
the
conclusion
that
a
law
ought
to
be
passed.
Such
questions
should
properly
be
decided
through
the
political
process,
the
appropriate
forum
for
taking
into
account
disparate
interests,
values,
and
alternative
approaches
(p
1534).6
It
would
be
presumptuous
for
me
to
express
a
preference
for
whether
Britain
should
or
should
not
pass
a
law
making
the
wearing
of
cycle
helmets
mandatory-
my
experience
goes
back
more
than
30
years
to
commuting
by
bicycle
without
wearing
a
helmet,
as
was
then
the
universal
custom,
to
universities
in
Belfast
and
Oxford.
My
plea
is
that
the
discussion
of
whether
or
not
to
pass
a
law
should
take
full
account
of
the
scientific
information
that
research
has
uncovered.
Robert
Oppenheimer
and
Edward
Teller
disagreed
passionately
over
whether
to
develop
thermonuclear
weapons,
but
they
had
no
disagreement
over
the
physics
on
which
they
were
based.
Discussions
on
whether
to
require
cyclists
to
wear
helmets
would
become
more
productive
if
everyone
would
accept
that
it
is
well
established
that
helmets
substantially
reduce
risk
in
a
crash,
and
that
passing
laws
making
wearing
them
mandatory
would
substantially
reduce
casualties.
LEONARD
EVANS
Principal
research
scientist
Automotive
Safety
and
Health
Research
Department,
Research
and
Development
Center,
General
Motors
Corporation,
Warren
MI
48090-9055,
United
States
1
Evans
L.
Traffic
safety
and
the
driver.
New
York:
Van
Nostrand
Reinhold,
1991.
2
Maimaris
C,
Summers
CL,
Browning
C,
Palmer
CR.
Injury
patterns
in
cyclists
attending
an
accident
and
emergency
department:
a
comparison
of
helmet
wearers
and
non-wearers.
BMJ
1994;308:
1537-40.
3
Evans
L.
Proceedings
of
the
38th
annual
conference
of
the
Association
for
the
Advancement
of
Automotive
Medicine,
Lyons,
France,
21-23
September
1994.
Des
Plaines,
Illinois:
Associaton
for
the
Advancement
of
Automotive
Medicine
(in
press).
4
Evans
L,
Frick
MC.
Helmet
effectiveness
in
preventing
motorcycle
driver
and
passenger
fatalities.
AccidAnalPrev
1988;20:447-58.
5
Maxwell
HC,
Vulcan
AP,
Finch
CF,
Newstead
SV.
Mandatory
bicycle
helmet
use
following
a
decade
of
helmet
promotion
in
Victoria,
Australia:
an
evaluation.
Accid
Anal
Prev
1994;26:
325-37.
6
Gilbert
K,
McCarthy
M.
Deaths
of
cyclists
in
London
1985-92:
the
hazards
of
road
traffic.
BMJ
1994;308:1
534-7.
Managing
clinical
risk
Makes
sense,
but
does
it
work?
The
number
of
negligence
claims
made
against
health
authorities
rose
dramatically
during
the
1980s.'
Since
Crown
Indemnity
was
introduced
in
1990
the
responsibility
for
meeting
these
claims
has
shifted
from
defence
organisations
to
health
authorities
and
NHS
trusts.
Settling
these
claims
in
England
currently
costs
an
estimated
C75m
a
year'-money
that
could
otherwise
be
spent
on
patient
care.
What
can
NHS
trusts
do
to
minimise
these
costs?
The
NHS
Executive
has
recently
issued
Risk
Management
in the
NHS,
which
recommends
to
chief
executives
that
"risk
management
.
.
.
is
no
longer
an
optional
extra."3
Four
categories
of
risk
management
are
identified:
risks
that
relate
to
clinical
care;
non-clinical
risks
to
patient
safety,
such
as
security
and
fire
hazards;
risks
to
the
health
of
the
workforce;
and
organisational
risks,
such
as
failure
to
safeguard
confi-
dential
information
and
unlicensed
use
of
computer
software.
But
how
does
risk
management
relate
to
clinical
care?
It
aims
at
reducing
adverse
events
(incidents
that
under
optimal
conditions
are
not
a
normal
consequence
of
a
patient's
disease
or
treatment)
that
might
lead
to
negligence
claims.
It
also
helps
to
resolve
claims
that
do
arise.4
There
are
four
phases
in
this
process:
identification,
analysis,
control,
and
funding.'
To
identify
and
analyse
risks,
NHS
trusts
can
audit
to
monitor
adverse
events-perhaps
through
incident
reporting
or
screening
case
notes-and
analyse
complaints
and
claims
data.
Risk
control
includes
the
introduction
of
guidelines
and
protocols,
continuing
education,
and
organisational
change.
Incident
reporting
plays
a
key
part
in
risk
control
by
allowing
a
rapid
response
to
an
adverse
event,
including
timely
and
appropriate
communication
with
the
patient
and
family,
support
for
staff,
and
thorough
record
taking.
Risk
funding
ensures
financial
protection
against
successful
negligence
claims.
This
may
be
through
the
creation
of
a
central
fund,
as
recently
proposed
by
the
NHS
Executive,
or
through
insurance
(though
trusts
are
discouraged
from
this
option).2
Clinical
risk
management
and
clinical
audit
overlap-both
seek
to
improve
the
quality
of
care,
but
risk
management
is
concerned
with
the
quality
of
care
only
as
much
as
better
quality
care
might
reduce
negligence
claims.
Epidemiological
evidence
from
the
United
States
suggests
that
this
is
not
necessarily
so.
The
Harvard
medical
practice
study,
which
screened
the
case
notes
of
a
stratified
random
sample
of
1522
BMJ
VOLUME
308
11
JUNE
1994
... This resulted in a 25% to 40% increase in motorcycle deaths. [14][15][16][17][18] These results strongly imply that wearing a helmet does NOT lead to large increases in risk taking. 18 ...
... [14][15][16][17][18] These results strongly imply that wearing a helmet does NOT lead to large increases in risk taking. 18 ...
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The effect of mandatory helmet laws on bicycle ridership and bicycle-related accidents: a rapid evidence review
Technical Report
Full-text available
  • Jul 2018
The purpose of this review is to investigate the effect of mandatory bicycle helmet legislation (MHL) in Australia with respect to: (Q1) ridership; and (Q2) the prevalence of bicycle-related accidents involving serious injury or fatality. From a total literature pool of 2523 studies, 18 were found to align with the screening criteria for the review questions (Q1: n=3; Q2: n = 15). The review highlights the extremely complex nature of identifying causal relationships between MHLs and both bicycle ridership and the prevalence of serious bicycle-related accidents. The reasons for this complexity are due to issues with sampling, and inevitable biases and confounders that affect the reliability of the collected data. Moreover, it is difficult isolate the effects of MHLs from other external factors (e.g. population growth, enhancement of cycling infrastructure). While there is some evidence that MHLs may not affect bicycle ridership, there is insufficient reliable evidence to draw robust conclusions. This is due to: (i) the small number of studies identified; (ii) conflicting evidence between studies; and (iii) issues of bias in the data collected. Several high-quality studies suggest a protective effect of MHLs in mitigating serious injuries and fatality in Australia, however the results are mixed when international studies are also considered. Most studies in Canada and the US have concluded that MHLs have not been effective in reducing bicyclerelated serious injury and fatality, while some studies suggest that the New Zealand MHL may have been effective
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Influences on the Risk of Injury of Bicyclists' Heads and Benefits of Bicycle Helmets in Terms of Injury Avoidance and Reduction of Injury Severity
Article
  • Apr 2014
This study deals with the risk of injury to the bicyclist's head and the benefits of wearing a bicycle helmet in terms of reduction of injury severity or even injury avoidance. The accident data of 4,245 injured bicyclists as a randomized sample, collected by a scientific research team within the GIDAS project (German In-Depth Accident Study) were analyzed. Given that head injuries result in approximately 40% of bicycle-related crashes, helmet usage provides a sensible first-level approach for improving incidence and severity of head injuries. The effectiveness of the bicycle helmet was examined using descriptive and multivariate analysis for 433 bicyclists with a helmet and 3,812 bicyclists without a helmet. Skull fractures, severe brain injuries and skull base fractures were up to 80% less frequent for bicyclists wearing a helmet. Among individuals 40 years of age and older, a significant increase of severe head injuries occurred if no helmet was used compared to younger persons with helmet.
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Neurosurgery in Vietnam
Article
  • Oct 1997
  • SURG NEUROL
The development and current state of Vietnamese neurosurgery is presented, in order to highlight the difficulties faced by neurosurgeons in Vietnam and other developing countries. Information has been collected personally by the authors in Vietnam. The conditions of neurosurgery endured by our neurosurgical colleagues in Vietnam are far inferior to those in the developed world, particularly in terms of training, educational aids, investigative and operating room equipment, and postoperative and rehabilitative care. The recent formation of the Neurosurgical Society of Vietnam will help to improve these conditions, but help and encouragement from neurosurgeons in the developed world will also be of much value. The instigation of preventive strategies will likely make a significant impact on the health costs of neurotrauma in Vietnam.
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Can we prevent accidental injury to adolescents? A systematic review of the evidence
Article
  • Jan 1996
As part of the Department of Health strategy The Health of the Nation, a systematic review of published and unpublished literature relating to the effectiveness of interventions in reducing accidental injury in the population aged 15-24 years was carried out. The literature was reviewed under the standard setting headings of road, work, home, and sports and leisure, and graded for quality of evidence and strength of recommendation using a scale published in the UK national epidemiologically based needs assessment programme. The most effective measures appear to be legislative and regulatory controls in road, sport, and workplace settings. Environmental engineering measures on the road and in sports have relatively low implementation costs and result in fewer injuries at all ages. There is little evidence that purely educational measures reduced injuries in the short term. Community based approaches may be effective in all age groups, and incentives to encourage safer behaviour hold promise but require further evaluation. The potential of multifactorial approaches seems greater than narrowly based linear approaches. Few interventions to reduce injury in adolescents have been rigorously evaluated using good quality randomised controlled trials, and where such evidence is available, fewer have been shown to be definitely worthwhile. Many studies relied on surrogate measures rather than actual injury rates, and substantial issues relating to the efficacy or implementation of preventive measures in adolescent and young adult populations remain unresolved.
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Prevalence of cycle helmet use in children
Article
  • Mar 1999
  • Paediatr Nurs
A survey was conducted over a five-day period on a cohort of 234 families attending a busy regional children's out-patient department in the South West of England. A significant result of the survey was that parental use of helmets strongly correlated with the use of helmets by children. In addition, income was not found to be a major factor in cycle helmet ownership except in the lowest income band.
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Risk compensation theory should be subject to systematic reviews of the scientific evidence
Article
  • Jul 2001
“Risk compensation theory should be subject to systematic reviews of the scientific evidence” (Thompson, Thompson, and Rivara) and “The risk compensation theory and bicycle helmets”(Adams and Hillman) plus authors' responses are being republished electronically in a different order at the authors' request to avoid any potential confusion ( Injury Prevention 2002; 8 :e1; http://www.injuryprevention.com/cgi/content/full/8/2/e1). They were previously published in June 2001 ( Injury Prevention 2001; 7 :86–91). Many readers of Injury Prevention are quite familiar with the debate over bicycle helmet use. The core of this debate is the opinion on one side that helmets are effective and thus should be worn, countered on the other side by the belief that risk compensation negates this protective effect of helmets. A systematic review on helmet effectiveness has been published in the Cochrane Library.1 The objective of the Cochrane review was to determine whether bicycle helmets reduce head, brain, and facial injury for bicyclists of all ages involved in a crash. The principles required of high quality evidence based reviews were followed: a comprehensive literature search, pre-established study selection criteria, and most importantly a critical review of study methods. A well conducted systematic review identifies and considers all the literature (peer reviewed, government reports, and unpublished papers), and rates the study quality. Appropriately, such reviews only include better designed and conducted studies. The evidence is then summarized across all the studies. The literature search for the Cochrane review yielded five studies meeting the pre-established criteria for inclusion. The strengths and weaknesses of five case-control studies of bicycle helmet effectiveness were carefully evaluated. The scientific evidence which indicates that bicycle helmets protect against head, brain, severe brain and facial (upper and mid-face) injuries has been well established. Additionally, the evidence indicates that helmets provide injury protection in all type of crashes including those involving motor …
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Organochlorine Pesticides and Polychlorinated Biphenyls in Human Adipose Tissue*
Article
Full-text available
  • Feb 1991
Halogenated organic compounds are highly lipophilic chemicals that are persistent in the environment as a result of their use and chemical stability. Some of these compounds are also present in the environment as metabolites or oxidation products of a parent compound or as by-products formed in the production of chlorinated compounds. Chronic exposure to the general population results mainly through the food chain. Because they are lipophilic, and because many are metabolized slowly, these chemicals tend to concentrate in body fat tissue. This contribution has described these halogenated organic compounds, discussed their use, regulation and prohibition throughout the world, and reviewed published studies on the levels of these chemicals found in the adipose tissue of humans and animals. For many years, residues of halogenated organic compounds have been detected in the human adipose tissue of individuals in a number of countries, including those in Europe, Asia, and Africa, as well as in the U.S. The levels detected have been used as an index of the level of general population exposure of these compounds over time. Over the past two decades, most countries have observed a steady decline of this level of exposure, reflecting a reduction in the use of these compounds, restrictions on or banning of their use, and a corresponding decrease in their environmental levels. The levels of concentrations vary from chemical to chemical as well as from isomer to isomer. Since the use of aldrin and dieldrin has now been banned or restricted in the U.S. and a number of other countries, residue levels have slowly decreased. Mean values in human adipose tissue in the U.S. and some foreign countries ranged from 0.04 to 0.40 ppm for dieldrin. Aldrin was detected only in Argentina and Poland in the 1970s and endrin was not detected anywhere at anytime. By 1978, all products containing BHC registered in the U.S. has been either discontinued or reformulated to incorporate lindane rather than BHC. The potential for exposure to BHC is virtually nonexistent in the U.S.; however, exposure to lindane is possible since products containing this chemical are still marketed, and used particularly in the manufacture of human medicine. DDT was banned for agricultural purposes in the U.S. in 1972, although it is still used elsewhere for public health vector control. Since the decline in use of DDT, however, the average levels of concentration have also declined. Heptachlor, chlordane, and trans-nonachlor (a component of both heptachlor and chlordane) are chlorinated cyclodienes.(ABSTRACT TRUNCATED AT 400 WORDS)
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Pesticides and PCB residues in human breast lipids and their relation to breast cancer
Article
  • Mar 1992
  • Arch Environ Health
The etiology of human breast cancer is unknown; accepted risk factors, e.g., menstrual, reproductive, and family histories, are implicated in less than half of all cases. Various halogenated hydrocarbons--acting as either co-carcinogens or promoting agents--which are derived from the environment and are concentrated in human fatty stores, may also play a role in breast cancer risk. A pilot study was undertaken to measure and compare levels of chemical residues in mammary adipose tissue from women with malignant and nonmalignant breast disease. Elevated levels of polychlorinated biphenyls, bis (4-chlorophenyl)-1,1 dichloroethene, and bis(4-chlorophenyl)-1,1,1 trichloroethane were found in fat samples from women with cancer, compared with those who had benign breast disease. These results, although preliminary, suggest a role for environmentally derived suspect carcinogens in the genesis of mammary carcinoma.
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Occurrence of Beta-Hexachlorocyclohexane in breast cancer patients
Article
  • Dec 1990
The residues of polycyclic aromatic hydrocarbon (PAH) and neutral organochlorine compounds in breast fat of 44 breast cancer patients and 33 women free of cancer were determined. No statistically significant differences appeared between the two comparison groups with regard to occurrence of PAH compounds. Of the neutral organochlorine compounds, residues of beta-hexachlorocyclohexane (HCH) were found more frequently in breast cancer patients. After adjusting for age and parity by stepwise logistic regression, beta-HCH remained a significant risk factor of breast cancer. Using a cutoff point for the residue level of beta-HCH in breast adipose tissue of more than 0.1 mg/kg fat, the odds ratio was 10.51 (95% CI, 2.00-55.26).
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A Meta-analysis of the Effect of Estrogen Replacement Therapy on the Risk of Breast Cancer
Article
  • May 1991
To quantify the effect of estrogen replacement therapy on breast cancer risk, we combined dose-response slopes of the relative risk of breast cancer against the duration of estrogen use across 16 studies. Using this summary dose-response slope, we calculated the proportional increase in risk of breast cancer for each year of estrogen use. For women who experienced any type of menopause, risk did not appear to increase until after at least 5 years of estrogen use. After 15 years of estrogen use, we found a 30% increase in the risk of breast cancer (relative risk, 1.3; 95% confidence interval [CI], 1.2 to 1.6). The increase in risk was largely due to results of studies that included premenopausal women or women using estradiol (with or without progestin), studies for which the estimated relative risk was 2.2 (CI, 1.4 to 3.4) after 15 years. Among women with a family history of breast cancer, those who had ever used estrogen replacement had a significantly higher risk (3.4; CI, 2.0 to 6.0) than those who had not (1.5; CI, 1.2 to 1.7).
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Helmet Effectiveness in Preventing Motorcycle Driver and Passenger Fatalities
Article
  • Jan 1989
  • ACCIDENT ANAL PREV
Helmet effectiveness in preventing fatalities to motorcycle drivers and passengers was determined by applying the double pair comparison method to the Fatal Accident Reporting System (FARS) data for 1975 through 1986. Motorcycles with a driver and a passenger, at least one of whom was killed, were used. In order to reduce as much as possible potentially confounding effects due to the dependence of survivability on sex and age, the analysis is confined to male drivers (there were insufficient female driver data), and to cases in which the driver and passenger age do not differ by more than three years. Motorcycle helmet effectiveness estimates are found to be relatively unaffected by performing the analyses in a number of ways different from that indicated above. It was found that helmets are (28 +/- 8)% effective in preventing fatalities to motorcycle riders (the error is one standard error), the effectiveness being similar for male and female passengers, and similar for drivers and passengers. An additional result found was that the fatality risk in the driver seat exceeds that in the passenger seat by (26 +/- 2)%. The 28% effectiveness found generates calculated fatality increases from repeal of mandatory helmet-wearing laws that are compatible with observed increases.
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Organochlorine compounds in human breast fat from deceased with and without breast cancer and in biopsy material from newly diagnosed patients undergoing breast surgery
Article
  • Jul 1984
Epidemiological studies have related the incidence of mammary cancer to the dietary intake of fat and/or meat. Since organochlorine compounds (e.g., polychlorinated biphenyls (PCB) and DDT (and its metabolite DDE] are accumulated in the adipose tissue it was tempting to suggest a relationship between levels of PCB and "DDT" (i.e., DDT + DDE) in breast fat tissue and the occurrence of mammary cancer. To elucidate this theory, the organochlorine levels of 14 breast fat tissue samples from breast cancer patients and similar samples from 18 deceased mammary cancer patients were compared to that of 21 similar samples from noncancer patients and finally to adipose tissue samples from 35 non-cancer autopsy specimens. No significant differences were traced. Thus it seems that the accumulation of PCB and DDT measured in breast fat tissue do not relate to the occurrence of mammary cancer.
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Polychlorinated Biphenyls (PCBs), Dibenzo-p-dioxins (PCDDs), and Dibenzofurans (PCDFs) as Antiestrogens in MCF-7 Human Breast Cancer Cells: Quantitative Structure-Activity Relationships
Article
  • May 1993
The concentration-dependent effects of several PCB, PCDD, and PCDF congeners and several commercial PCB preparations as antiestrogens were determined in the aryl hydrocarbon (Ah)-responsive MCF-7 human breast cancer cell lines. The inhibition of the 17 beta-estradiol-induced secretion of the 52-kDa protein (procathepsin D) was measured using a combination of polyacrylamide gel electrophoresis, double-staining of the protein bands with ISS ProBlue and silver stain, and quantitation by densitometric analysis. For the PCBs, the order of antiestrogenic potency was 3,3',4,4',5-pentachlorobiphenyl > 3,3',4,4',5,5'-hexachlorobiphenyl approximately 3,3',4,4'-tetrachlorobiphenyl > 2,3,3',4,4',5'-hexa, 2,3,3',4,4'- and 2,3,4,4',5-pentachlorobiphenyl > Aroclors 1221, 1232, 1248, 1254, and 1260 were inactive as antiestrogens at the highest concentrations used in this study (10(-6) M). For the PCDDs and PCDFs, the order of antiestrogenic potency was 2,3,7,8-tetrachlorodibenzo-p-dioxin > 2,3,7,8-tetrachlorodibenzofuran > 2,3,4,7,8-pentachlorodibenzofuran > 1,2,3,7,9-pentachlorodibenzofuran > 1,3,6,8-tetrachlorodibenzofuran. With few exceptions, the order of potency for all these congeners and mixtures paralleled their relative activities as agonists for other Ah receptor-mediated responses and their competitive binding affinities for the Ah receptor. The results of this study support the role for the Ah receptor in mediating the inhibition of the 17 beta-estradiol-induced secretion of the 52-kDa protein in MCF-7 cells and also points out the utility of this technique as a bioassay for this class of compounds.
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Mandatory bicycle helmet use following a decade of helmet promotion in Victoria, Australia-An evaluation
Article
  • Jul 1994
  • ACCIDENT ANAL PREV
On July 1, 1990, a law requiring wearing of an approved safety helmet by all bicyclists (unless exempted) came into effect in Victoria, Australia. Some of the more important steps that paved the way for this important initiative (believed to be the first statewide legislation of its type in the world) are described, and the initiative's effects are analysed. There was an immediate increase in average helmet-wearing rates from 31% in March 1990 to 75% in March 1991, although teenagers continued to show lower rates than younger children and adults. The number of insurance claims from bicyclists killed or admitted to hospital after sustaining a head injury decreased by 48% and 70% in the first and second years after the law, respectively. Analysis of the injury data also showed a 23% and 28% reduction in the number of bicyclists killed or admitted to hospital who did not sustain head injuries in the first and second post-law years, respectively. For Melbourne, where regular annual surveys of helmet wearing have been conducted, it was possible to fit a logistic regression model that related the reduction in head injuries to increased helmet wearing. Surveys in Melbourne also indicated a 36% reduction in bicycle use by children during the first year of the law and an estimated increase in adult use of 44%.
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Injury patterns in cyclists attending an accident and emergency department: A comparison of helmet wearers and non-wearers
Article
  • Jun 1994
To study circumstances of bicycle accidents and nature of injuries sustained and to determine effect of safety helmets on pattern of injuries. Prospective study of patients with cycle related injuries. Accident and emergency department of teaching hospital. 1040 patients with complete data presenting to the department in one year with cycle related injuries, of whom 114 had worn cycle helmets when accident occurred. Type of accident and nature and distribution of injuries among patients with and without safety helmets. There were no significant differences between the two groups with respect to type of accident or nature and distribution of injuries other than those to the head. Head injury was sustained by 4/114 (4%) of helmet wearers compared with 100/928 (11%) of non-wearers (P = 0.023). Significantly more children wore helmets (50/309 (16%)) than did adults (64/731 (9%)) (P < 0.001). The incidence of head injuries sustained in accidents involving motor vehicles (52/288 (18%)) was significantly higher than in those not involving motor vehicles (52/754 (7%)) (chi 2 = 28.9, P < 0.0001). Multiple logistic regression analysis of probability of sustaining a head injury showed that only two variables were significant: helmet use and involvement of a motor vehicle. Mutually adjusted odds ratios showed a risk factor of 2.95 (95% confidence interval 1.95 to 4.47, P < 0.0001) for accidents involving a motor vehicle and a protective factor of 3.25 (1.17 to 9.06, P = 0.024) for wearing a helmet. The findings suggest an increased risk of sustaining head injury in a bicycle accident when a motor vehicle is involved and confirm protective effect of helmet wearing for any bicycle accident.
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