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Studies of risk perception examine the judgements people make when they are asked to characterize and evaluate hazardous activities and technologies. This research aims to aid risk analysis and policy-making by providing a basis for understanding and anticipating public responses to hazards and improving the communication of risk information among lay people, technical experts, and decision-makers. This work assumes that those who promote and regulate health and safety need to understand how people think about and respond to risk. Without such understanding, well-intended policies may be ineffective.
Content may be subject to copyright.
as
potent
as
carcinogens
such
as
symphytine.
If
the
other
pyrrolizidine
alkaloids
in
comfrey
were
as
potent
carcinogens
as
symphytine,
the
possible
hazard
of
a
dailv
cup
of
tea
would
be
HERP
=
0.6%
and
that
of
a
daily
nine
tablets
would
be
HERP=
7.3%.
104.
Agarcus
bisporfs
is
the
most
commonly
eaten
mushroom
in
the
United
States
with
an
estimated
annual
consumption
of
340
million
kilograms
in
1984-85.
Mush-
rooms
contain
various
hvdrazine
compounds,
some
of
which
have
been
shown
to
cause
tumors
in
mice.
Raw
mushrooms
fed
over
a
lifetime
to
male
and
female
mice
induced
bone,
forestomach,
liver,
and
lung
tumors
[B.
Toth
and
J.
Erickson,
Cancer
Res.
46,
4007
(1986)].
The
15-g
raw
mushroom
is
given
as
wet
weight.
The
TD50
value
based
on
the
above
report
is
expressed
as
dry
weight
of
mushrooms
so
as
to
be
comparable
to
other
values
for
TD50
in
Table
1;
90%
of
a
mushroom
is
assumed
to
be
water.
A
second
mushroom,
Gyromitra
escuknta,
has
been
similarlv
studied
and
found
to contain
a
mixture
of
carcinogenic
hvdrazines
[B.
Toth,J.
Environ.
Sci.
Health
C2,
51
(1984)].
These
mushrooms
are
eaten
in
considerable
quantities
in
several
countries,
though
less
frequently
in
the
United
States.
105.
Safrole
is
the
main
component
(up
to
90%)
of
oil
of
sassafras,
formerly
used
as
the
main
flavor
ingredient
in
root
beer
[J.
B.
Wilson,
J.
Assoc.
Off
Anal.
Chem.
42,
696
(1959);
A.
Y.
Leung,
Encyclopedia
of
Common
Natural
Ingredients
Used
in
Food,
Drugs
and
Cosmetics
(Wiley,
New
York,
1980)].
In
1960,
safrole
and
safrole-
containing
sassafras
oils
were
banned
from
use
in
foods
in
the
United
States
[Fed.
Regist.
25,
12412
(1960)].
Safrole
is
also
naturally
present
in
the
oils
of
sweet
basil,
cinnamon
leaf,
nutmeg,
and
pepper.
106.
Diet
cola
available
in
a
local
market
contains
7.9
mg
of
sodium
saccharin
per
fluid
ounce.
107.
Metronidatole
is
considered
to
be
the
drug
of
choice
for
trichomonal
and
Gardnerella
infections
[AMA
Division
of
Drugs,
AMA
Drug
Evaluations
(Ameri-
can
Medical
Association,
Chicago,
IL,
ed.
5,
1983),
pp.
1717
and
1802].
108.
Isoniazid
is
used
both
prophylactically
and
as
a
treatment
for
active
tuberculosis.
The
adult
prophylactic
dose
(300
mg
daily)
is
continued
for
1
year
[AMA
Division
of
Drugs,
AMA
Drug
Evaluations
(American
Medical
Association,
Chicago,
IL,
ed.
5,
1983),
pp.
1766-1777].
109.
D
M.
Siegal,
V.
H.
Frankos,
M.
A.
Schneiderman,
Reg.
Toxicol.
Pharmacol.
3,
355
(1983).
110.
Supported
by
NCI
Outstanding
Investigator
Grant
CA39910
to
B.N.A.,
NIEHS
Centc
Grant
ES01896,
and
NIEHS/DOE
Interagency
Agreement
222-YOl-ES-
10066.
We
are
indebted
to
numerous
colleagues
for
criticisms,
particularly
W.
Havender,
R.
Peto,
J.
Cairns,
J.
Miller,
E.
Miler,
D.
B.
Clayson,
J.
McCann,
and
F.
J.
C.
Roe.
Perception
of
Risk
PAUL
SLOVIC
Studies
of
risk
perception
examine
the
judgments
people
make
when
they
are
asked
to
characterize
and
evaluate
hazardous
activities
and
technologies.
This
research
aims
to
aid
risk
analysis
and
policy-making
by
(i)
providing
a
basis
for
understanding
and
anticipating
public
responses
to
hazards
and
(ii)
improving
the
communication
of
risk
information
among
lay
people,
technical
experts,
and
decision-makers.
This
work
assumes
that
those
who
pro-
mote
and
regulate
health
and
safety
need
to
understand
how
people
think
about
and
respond
to
risk.
Without
such
understanding,
well-intended
policies
may
be
inef-
fective.
T
HE
ABILITY
TO
SENSE
AND
AVOID
HARMFUL
ENVIRONMEN-
tal
conditions
is
necessary
for
the
survival
of
all
living
organisms.
Survival
is
also
aided
by
an
ability
to
codify
and
learn
from
past
experience.
Humans
have
an
additional
capability
that
allows
them
to
alter
their
environment
as
well
as
respond
to
it.
This
capacity
both
creates
and
reduces
risk.
In
recent
decades,
the
profound
development
of
chemical
and
nuclear
technologies
has
been
accompanied
by
the
potential
to
cause
catastrophic
and
long-lasting
damage
to
the
earth
and
the
life
forms
that
inhabit
it.
The
mechanisms
underlying
these
complex
technolo-
gies
are
unfamiliar
and
incomprehensible
to
most
citizens.
Their
most
harmful
consequences
are
rare
and
often
delayed,
hence
difficult
to
assess
by
statistical
analysis
and
not
well
suited
to
management
by
trial-and-error
learning.
The
elusive
and
hard
to
manage
qualities
of
today's
hazards
have
forced
the
creation
of
a
new
intellectual
discipline
called
risk
assessment,
designed
to
aid
in
identifying,
characterizing,
and
quantifying
risk
(1).
Whereas
technologically
sophisticated
analysts
employ
risk
assess-
ment
to
evaluate
hazards,
the
majority
of
citizens
rely
on
intuitive
risk
judgments,
typically
called
"risk
perceptions."
For
these
people,
280
experience
with
hazards
tends
to
come
from
the
news
media,
which
rather
thoroughly
document
mishaps
and
threats
occurring
throughout
the
world.
The
dominant
perception
for
most
Ameri-
cans
(and
one
that
contrasts
sharply
with
the
views
of
professional
risk
assessors)
is
that
they
face
more
risk
today
than
in
the
past
and
that
future
risks
will
be
even
greater
than
today's
(2).
Similar
views
appear
to
be
held
by
citizens
of
many
other
industrialized
nations.
These
perceptions
and
the
opposition
to
technology
that
accompa-
nies
them
have
puzzled
and
frustrated
industrialists
and
regulators
and
have
led
numerous
observers to
argue
that
the
American
public's
apparent
pursuit
of
a
"zero-risk
society"
threatens
the
nation's
political
and
economic
stability.
Wildavsky
(3,
p.
32)
commented
as
follows
on
this
state
of
affairs.
How
extraordinary!
The
richest,
longest
lived,
best
protected,
most
resourceful
civilization,
with
the
highest
degree
of
insight
into
its
own
technology,
is
on
its
way
to
becoming
the
most
frightened.
Is
it
our
environment
or
ourselves
that
have
changed?
Would
people
like
us
have
had
this
sort
of
concern
in
the
past?
.
.
.
Today,
there
are
risks
from
numerous
small
dams
far
exceeding
those
from
nuclear
reactors.
Why
is
the
one
feared
and
not
the
other?
Is
it
just
that
we
are
used
to
the
old
or
are
some
of
us
looking
differently
at
essentially
the
same
sorts
of
experience?
During
the
past
decade,
a
small
number
of
researchers
has
been
attempting
to
answer
such
questions
by
examining
the
opinions
that
people
express
when
they
are
asked,
in
a
variety
of
ways,
to
evaluate
hazardous
activities,
substances,
and
technologies.
This
research
has
attempted
to
develop
techniques
for
assessing
the
complex
and
subtle
opinions
that
people
have
about
risk.
With
these
techniques,
researchers
have
sought
to
discover
what
people
mean
when
they
say
that
something
is
(or
is
not)
"risky,"
and
to
determine
what
factors
underlie
those
perceptions.
The
basic
assumption
underlying
these
efforts
is
that
those
wvho
promote
and
regulate
health
and
safety
need
to
understand
the
ways
in
which
people
think
about
and
respond
to
risk.
The
author
is
prcsident
of
Decision
Research,
1201
Oak
Street,
Eugene,
OR
97401,
and
professor
of
psychology
at
the
University
of
Oregon.
SCIENCE,
VOL.
236
on February 1, 2010 www.sciencemag.orgDownloaded from
If
successful,
this
research
should
aid
policy-makers
by
improving
communication
between
them
and
the
public,
by
directing
educa-
tional
efforts,
and
by
predicting
public
responses
to
new
technolo-
gies
(for
example,
genetic
engineering),
events
(for
example,
a
good
safety
record
or
an
accident),
and
new
risk
management
strategies
(for
example,
warning
labels,
regulations,
substitute
products).
Risk
Perception
Research
Important
contributions
to
our
current
understanding
of
risk
perception
have
come
from
geography,
sociology,
political
science,
anthropology,
and
psychology.
Geographical
research
focused
orig-
inally
on
understanding
human
behavior
in
the
face
of
natural
hazards,
but
it
has
since
broadened
to
include
technological
hazards
as
well
(4).
Sociological
(5)
and
anthropological
studies
(6)
have
shown
that
perception
and
acceptance
of
risk
have
their
roots
in
social
and
cultural
factors.
Short
(5)
argues
that
response
to
hazards
is
mediated
by
social
influences
transmitted
by
friends,
family,
fellow
workers,
and
respected
public
officials.
In
many
cases,
risk
percep-
tions
may
form
afterwards,
as
part
of
the
ex
post
facto
rationale
for
one's
own
behavior.
Douglas
and
Wildavsky
(6)
assert
that
people,
acting
within
social
groups,
downplay
certain
risks
and
emphasize
others
as
a
means
of
maintaining
and
controlling
the
group.
Psychological
research
on
risk
perception,
which
shall
be
my
focus,
originated
in
empirical
studies
of
probability
assessment,
utility
assessment,
and
decision-making
processes
(7).
A
major
development
in
this
area
has
been
the
discovery
of
a
set
of
mental
strategies,
or
heuristics,
that
people
employ
in
order
to
make
sense
out
of
an
uncertain
world
(8).
Although
these
rules
are
valid
in
some
circumstances,
in
others
they
lead
to
large
and
persistent
biases,
with
serious
implications
for
risk
assessment.
In
particular,
laboratory
research
on
basic
perceptions
and
cognitions
has
shown
that
difficul-
ties
in
understanding
probabilistic
processes,
biased
media
coverage,
misleading
personal
experiences,
and
the
anxieties
generated
by
life's
gambles
cause
uncertainty
to
be
denied,
risks
to
be
misjudged
(sometimes
overestimated
and
sometimes
underestimated),
and
judgments
of
fact
to
be
held
with
unwarranted
confidence.
Experts'
judgments
appear
to
be
prone
to
many
of
the
same
biases
as
those
of
the
general
public,
particularly
when
experts
are
forced
to
go
beyond
the
limits
of
available
data
and
rely
on
intuition
(8,
9).
Research
further
indicates
that
disagreements
about
risk
should
not
be
expected
to
evaporate
in
the
presence
of
evidence.
Strong
initial
views
are
resistant
to
change
because
they
influence
the
way
that
subsequent
information
is
interpreted.
New
evidence
appears
reliable
and
informative
if
it
is
consistent
with
one's
initial
beliefs;
contrary
evidence
tends
to
be
dismissed
as
unreliable,
erroneous,
or
unrepresentative
(10).
When
people
lack
strong
prior
opinions,
the
opposite
situation
exists-they
are
at
the
mercy
of
the
problem
formulation.
Presenting
the
same
information
about
risk
in
different
ways
(for
example,
mortality
rates
as
opposed
to
survival
rates)
alters
people's
perspectives
and
actions
(11).
The
Psychometric
Paradigm
One
broad
strategy
for
studying
perceived
risk
is
to
develop
a
taxonomy
for
hazards
that
can
be
used
to
understand
and
predict
responses
to
their
risks.
A
taxonomic
scheme
might
explain,
for
example,
people's
extreme
aversion
to
some
hazards,
their
indiffer-
ence
to
others,
and
the
discrepancies
between
these
reactions
and
opinions
of
experts.
The
most
common
approach
to
this
goal
has
employed
the
psychometric
paradigm
(12,
13),
which
uses
psycho-
physical
scaling
and
multivariate
analysis
techniques
to
produce
17
APRIL
I987
quantitative
representations
or
"cognitive
maps"
of
risk
attitudes
and
perceptions.
Within
the
psychometric
paradigm,
people
make
quantitative
judgments
about
the
current
and
desired
riskiness
of
diverse
hazards
and
the
desired
level
of
regulation
of
each.
These
judgments
are
then
related
to
judgments
about
other
properties,
such
as
(i)
the
hazard's
status
on
characteristics
that
have
been
hypothesized
to
account
for
risk
perceptions
and
attitudes
(for
example,
voluntariness,
dread,
knowledge,
controllability),
(ii)
the
benefits
that
each
hazard
provides
to
society,
(iii)
the
number
of
deaths
caused
by
the
hazard
in
an
average
year,
and
(iv)
the
number
of
deaths
caused
by
the
hazard
in
a
disastrous
year.
In
the
rest
of
this
article,
I
shall
briefly
review
some
of
the
results
obtained
from
psychometric
studies
of
risk
perception
and
outline
some
implications
of
these
results
for
risk
communication
and
risk
management.
Revealed
and
Expressed
Preferences
The
original
impetus
for
the
psychometric
paradigm
came
from
the
pioneering
effort
of
Starr
(14)
to
develop
a
method
for
weighing
technological
risks
against
benefits
in
order
to
answer
the
fundamen-
tal
question,
"How
safe
is
safe
enough?"
His
"revealed
preference"
approach
assumed
that,
by
trial
and
error,
society
has
arrived
at
an
"essentially
optimum"
balance
between
the
risks
and
benefits
associ-
ated
with
any
activity.
One
may
therefore
use
historical
or
current
risk
and
benefit
data
to
reveal
pattems
of
"acceptable"
risk-benefit
trade-offs.
Examining
such
data
for
several
industries
and
activities,
Table
1.
Ordering
of
perceived
risk
for
30
activities
and
technologies
(22).
The
ordering
is
based
on
the
geometric
mean
risk
ratings
within
each
group.
Rank
1
represents
the
most
risky
activity
or
technology.
Activity
League
of
College
Active
or
Women
students
club
Experts
technology
Voters
members
Nuclear
power
1
1
8
20
Motor
vehicles
2
53
1
Handguns
3
2
1
4
Smoking
4
3
4
2
Motorcycles
5
6
2
6
Alcoholic
beverages
67
5
3
General
(private)
7
15
11
12
aviation
Police
work
8
8
7
17
Pesticides
9
4
15
8
Surgery
10
11
9
5
Fire
fighting
11
10
6
18
Large
construction
12
14
13
13
Hunting
13
18
10
23
Spray
cans
14
13
23 26
Mountain
climbing
15
22
12
29
Bicycles
16
24
14
15
Commercial
aviation
17
16
18 16
Electric
power
(non-
18
19
19
9
nuclear)
Swimming
19
30
17
10
Contraceptives
20
9
22
11
Skiing
21
25
16
30
X-rays
22
17
24
7
High
school
and
23
26
21
27
college
football
Rairoads
24
23
29
19
Food
preservatives
25
12
28
14
Food
coloring
26
20
30
21
Power
mowers
27
28
25
28
Prescription
antibiotics
28
21
26 24
Home
appliances
29
27
27
22
Vaccinations
30
29 29
25
ARTICLES
28I
on February 1, 2010 www.sciencemag.orgDownloaded from
Starr
concluded
that
(i)
acceptability
of
risk
from
an
activity
is
roughly
proportional
to
the
third
power
of
the
benefits
for
that
activity,
and
(ii)
the
public
will
accept
risks
from
voluntary
activities
(such
as
skiing)
that
are
roughly
1000
times
as
great
as
it
would
tolerate
from
involuntary
hazards
(such
as
food
preservatives)
that
provide
the
same
level
of
benefits.
The
ments
and
deficiencies
of
Starr's
approach
have
been
debated
at
length
(15).
They
will
not
be
elaborated
here,
except
to
note
that
concem
about
the
validity
of
the
many
assumptions
inherent
in
the
revealed
preferences
approach
stimulated
Fischhoff
et
al.
(12)
to
conduct
an
analogous
psychometric
analysis
of
questionnaire
data,
resulting
in
"expressed
preferences."
In
recent
years,
numerous
other
studies
of
expressed
preferences
have
been
carried
out
within
the
psychometric
paradigm
(16-24).
These
studies
have
shown
that
perceived
risk
is
quantifiable
and
predictable.
Psychometric
techniques
seem
well
suited
for
identify-
ing
similarities
and
differences
among
groups
with
regard
to
risk
perceptions
and
attitudes
(Table
1).
They
have
also
shown
that
the
Factor
2
Unknown
risk
Laetrile*
Microwave
ovens
-
Water
Fluoridation0
Saccharin
.
Ni
tri
tesl
*
Hexachlorophene
Water
Chlorination
i
Polyvinyl
Ch'orideg
Coal
Tar
Hairdyes5
Oral
Contraceptivese
*
Diagnostic
X
Rays
Valium
DarvonO*
*
IuD
Antibiotics*
Rubber
Mfg
-
*
Caffeine
*
Aspi
ri
n
Auto
Lead
T
*
Lead
Paint
*
Vaccilnes
Power
Mowers
4
I
' I
'
'
'
'
w
' '
Skateboards
*
Smoking
(Disease)
*
Snowmobiles
*
rrampolines
0
*
Tractors
Alcohol-
Chainsaws*
*
Elevators
Home
Swimming
Pools5
S
Electric
Wir
&
Appl
(Fires)
Downhill
Skiing!
*
Smoking
(Fires)
Rec
Boating
5
Electric
Wir
&
Appl
(Shock)o
Bicycles*
Motorcycles*
Bridges5
*
Fireworks
*
*
DNA
Technology
.
*Electric
Fields
*
DES
.-
*
Nitrogen
Fertilizers
0
SST
-
*Cadmium
Usage
*Mirex
*Trichloroethylene
*2,4.5-T
*
Pesticides
6
*
Asbestos
Insulation
*
PCS's
*
Mercury
*DDT
Satellit
*
Fossil
Fuels
*Coal
Burning
(Pollution)
a
a
a
a
a
a
I
_-
*
Auto
Exhaust
(CO)
*
0-CON
*P
Radioactive
Waste
*
Nuclear
Reactor
Accidents
0
Uranium
Mining
*Nuclear
Weapons
Fallout
te
Crashes
Factor
1
Dread
risk
I
SING
SrIr
p
I
N
G
A
ccIe
,
*
LNG
Storage
&
Transport
Nerve
Gas
Accidents
*
Coal
Mining
(Disease)
5
Large
Dams
*
Skyscraper
Fires
Nuclear
Weapons
(War)*
*
Underwater
Const
*
Sport
Parachutes
*
General
Aviation
S
Coal
Mining
Accidents
*
High
Construction
*
Railroad
Collisions
Alcohol
Accidents
*
Coenm
Aviation
*
Auto
Racing
OAuto
Accidents
-
*p
Handguns
*
Dynamite
Factor
2
CONTROLLABLE
NOT
DREAD
NOT
GLOBAL
CATASTROPHIC
CONSEQUENCES
NOT
FATAL
EQUITABLE
INDIVIDUAL
LOW
RISK
TO
FUTURE
GENERATIONS
EASILY
REDUCED
RISK
DECREASING
VOLUNTARY
NOT
OBSERVABLE
UNKNOWN
TO
THOSE
EXPOSED
EFFECT
DELAYED
NEW
RISK
RISKS
UNKNOWN
TO
SCIENCE
UNCONTROLLABLE
DREAD
GLOBAL
CATASTROPHIC
CONSEQUENCES
FATAL
NOT
EQUITABLE
CATASTROPHIC
HIGN
RISK
TO
FUTURE
GENERATIONS
NOT
EASILY
REDUCED
RISK
INCREASING
INVOLUNTARY
Fig.
1.
Location
of
81
hazards
on
factors
1
and
2
derived
from
the
relationships
among
18
risk characteristics.
Each
factor
is
made
up
of
a
combination
of
characteristics,
as
indicated
by
the
lower
diagram
(25).
Factor
1
.
A
I
I
.
.
.
.
i i
. .
.
.
.
.
. .
.
.
. .
.
. . .
o
.
.
...
. . .
. . .
.
. . .
I
I I
v
i
I
.
.
I
I
I
I
v
v
I
I
.
I
.
9
I
.
A
I
I
I
I
I
I 1
-
a
I
a
A
a
a
a
a
I I
I
I
I
.
I
.
I
.
I
I
a
I
l1
I
Ia
a
.
.
.
a
.
.
.
6
-
-T
282
SCIENCE3
VOL.
236
on February 1, 2010 www.sciencemag.orgDownloaded from
concept
"risk"
means
different
things
to
different
people.
When
experts
judge
risk,
their
responses
correlate
highly
with
technical
estimates
of
annual
fatalities.
Lay
people
can
assess
annual
fatalities
if
they
are
asked
to
(and
produce
estimates
somewhat
like
the
technical
estimates).
However,
their
judgments
of
"risk"
are
related
more
to
other
hazard
characteristics
(for
example,
catastrophic
potential,
threat
to
future
generations)
and,
as
a
result,
tend
to
differ
from
their
own
(and
experts')
estimates
of
annual
fatalities.
Another
consistent
result
from
psychometric
studies
of
expressed
preferences
is
that
people
tend
to
view
current
risk
levels
as
unacceptably
high
for
most
activities.
The
gap
between
perceived
and
desired
risk
levels
suggests
that
people
are
not
satisfied
with
the
way
that
market
and
other<