On the Origin of Hill's Causal Criteria Author(s): Alfredo Morabia Source: Epidemiology, Vol. 2, No. 5 (Sep., 1991), pp. 367-369 Published by: Lippincott Williams & Wilkins Stable URL: http://www.jstor.org/stable/20065702 Accessed: 06/01/2010 11:15 Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available at http://www.jstor.org/page/info/about/policies/terms.jsp. JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content in the JSTOR archive only for your personal, non-commercial use. Please contact the publisher regarding any further use of this work. Publisher contact information may be obtained at http://www.jstor.org/action/showPublisher?publisherCode=lww. Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printed page of such transmission. JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact
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On the Origin of Hill's Causal Criteria Alfredo Morabia
The
to assess
rules
Hill's
Bradford
Hume's
of whether
causation work
was
"The
as opposed
D. Hume,
causality,
Environment
lack of
The
contemporary epidemiologists. and Hill's, analogy of Hume's Keywords:
A.B.
research
on
association.
As
recently
the noted
in
Here I compare the causal criteria formulated by Hume and by Hill. A first contrast is of historical nature. In
of
1740,
or Causa
reference nature
causal
in a review
by
Susser,2 Hill codified in his paper a set of criteria that had since 1955.3"6 been elaborated by several epidemiologists Part of these criteria was applied in assessing the causal relation
between
cigarette
and
smoking
cancer
lung
in
to the US the 1964 Report of the Advisory Committee Surgeon General, Smoking and Health.1 The rationale was that a finding satisfying several criteria was more likely to be causal than one that satisfied only a few or none. While reading David Hume's A Treatise of Human Nature,8 I came upon the "rules by which to judge of causes and effects" (pp. 173-176) and was struck by their to HilPs
similarities proaches
to
criteria. To in
causality
find
contemporary
and in an eighteenth century philosopher raised the question of the philosophic criteria that, to my knowledge, has not heretofore. In addition, a potential link
analogous
ap
epidemiologists
was puzzling. It roots of Hill's been addressed between Hume
and Hill
(read: between Hume and the generation of epidemiologists who contributed to the elaboration of the criteria efficiently summarized by Hill) suggested that there could be a parallelism between the Popper-Hume and the Popper-Hill controversies. The first controversy is
now
controversy, generated
to
well-known
initiated
a variety
epidemiologists.9
The
to Hill's
criteria,
from rejection of the criteria reflecting inductive rejection of the method itself.12
From the Clinical Micheli-du-Crest
second
15 years ago by Carol Buck,10 has
of criticisms
1991;2;367?369)
(Epidemiology
K. Popper.
is a classic
assessing
a point of view still widely shared by expresses thinking to causal in epidemiology inferences the may explain
proof
experimental logic.
Association
tion," by Sir A. Bradford Hill,1 epidemiologic an observed
systematic
to Popper's,
Hill,
Disease:
and
are compared to Sir Austin David Hume philosopher rules and Hill's causal criteria that, irrespective suggests
Scottish century by the eighteenth Hume's of the analogy between strength to Hill or Hill's Hume's known predecessors, formulated
The
criteria.
causal
Epidemiology Unit, University Canton 25, 1211 Geneva 4, Switzerland.
ranging
logic11 to
Hospital,
mental
?
1991 Epidemiology
Primus
Resources
Inc.
for assistance
in the preparation
was
method
not
the
but
emerging, a system
yet
of
experi
research.
Hume
believed that observations were fragile bases for causal inferences and that the discovery of causes required an intellectual process going "beyond the impression of our senses."
He
therefore
a process.
such
a set of
proposed
In contrast,
Hill
and
to structure
rules his
contemporary
epidemiologist colleagues, concerned by the biases result ing from the "method of observation" in studying human populations,13 tried to define the circumstances in which we
can
infer
causation
from
observa
nonexperimental
tion.
Methods I have tried to match Hill's are
in
expressed
and Hume's two
their
criteria as they Because
publications.1'8
treatise was published 225 years before Hill's it is obviously impossible to get a perfect match. report,
Hume's For
example,
Hume
his
presented
as
rules
statements, whereas Hill's criteria are worded for preventive
medicine.
My
goal,
light on a potential philosophical the formulation itself.
universal
specifically was
however,
to
shed
kinship rather than on
Results The
of Hume's
comparison
rized inTable 1. The conceptual called
and Hill's
is striking for what Hill has
identity
"temporality,"
is summa
criteria
"biologic
gradient,"
and
"consis
tency." The temporality criterion is stated explicitly by both Hume and Hill. Hill: "The temporal relationship of is the cart and which the association?which is the Rue
horse?" in space
The author thanks Maryline the manuscript.
were
sciences
empirical
of
Hume: and
"The time.
The
cause
and
cause
(Rules land 2). The concept of gradient associations is also mentioned
effect
must
must
be prior
be
contiguous
to the
effect"
as a support for causal by both authors, but for
367
MORABIA
1. Hill's Criteria* and Corresponding Hume's
TABLE
"Rules
to Judge
by which
of Causes
mu?a
and
Effects"t Hill's
Hume's
Criteria
Rules cause must
1. "The
2. Dose-response
2.
3. Consistency
3.
of association
be prior
to
criterion
cause"
7. Biological plausibility
7. Not applicable4 8. Not
Experiment
tion.
we
then
curve,
...
evidence.
should
The
clear
or diminishes
its
to
'tis
cause,
with
be
a
as
regarded
dose-response
and obviously puts "When any object
increase
the
most
look
or diminution
some
"In
Hill:
rule.
viral
Hume's
example, and
effect,
circum
in pregnancy."
disease
(Rule 4)
always
never
effect
echoes
produces
arises
but
from
criterion
Hill's
of
reasons, two remaining criteria listed by have no plausibility and experiment) set
in Hume's
of
It would
rules.
an
be
anachronism to find the concept of biological plausibility in the writing of a seventeenth century philosopher. Also, although a contemporary of Newton, Hume (1711-1776) was a preexperimental thinker. Experimental method became
a
century,
after
of
system
research
the works
and
others.
agreed with Hume's
causation,
the
emphasized
without
cannot
but
Indeed,
approach on
of experiment: can ascertain
role
experimentation
co-existences,
nineteenth
the
during
of Lavoisier
John Stuart Mill, who
and
effect,
cause
"same same
the
same cause"
tion
of
compounded
sixth
or another
drug
counterpart
curve admits of a simple explanation the case in a clearer light." Hume: increases
Hume's
specificity. For historical Hill (biological
applicable.^:
Hume this is a sufficient causal criterion. Hill: "If the association is one which can reveal a biological gradient, carefully
For same
the
1. *Source: Reference f Source: Reference 8, pp. 173-176. $See Results section.
such
constant
Hume: "Where several different objects produce the same effect, itmust be by means of some quality, which we discover to be common amongst them" (Rule 5). "Like effects imply like causes" (Rule 6). It is possible to find in Hume's writing formulas that correspond to Hill's criteria of specificity and coherence.
the
4).
(Rule
8.
for
a
be
the importance lies in the similarity of the Again, intellectual approach rather than in the exact formula
causes" (Rule 6). "Same cause always produces the same effect, and the same effect never arises but from
6.
dose-response
of association
must
it would
another
with
rule but in the premises of the p. 163). catalog, "There must be a constant union betwixt the cause and
the same
or
a measure
risk, "There
be fair to judge by analogy. With the effects of thalidomide and rubella before us we should surely be ready to accept slighter but similar evidence
effect" (Rule 3). 5. "Like effects imply like
Specificity
and
stances
increases "When any object or diminishes with the or diminution increase of its cause" (Rule 7). of resembling "Multiplicity instances constitutes the very essence of power or connexion" (not a specific
4.
5. Analogy 6.
relative
betwixt the cause and effect. 'Tis chiefly this quality, that constitutes the relation" (Rule 3). is some resemblance between Hill's analogy There
the effect" (Rules 1 and 2).
Strength
the
causation:
of
than
union
1. Temporality
4.
like
is, just
rather
"Observa sequences
causation."14
prove
deriv'd from the union of the several different effects, which arise from the several different parts of the cause. The
of
criterion
second
proves
sufficiently
conjunction
is the cause of the other" Hill's
part
cause
the
is here
to be always attended with the absence or of a proportionable part of the effect. This
suppos'd presence constant
of one
or presence
absence
the one
that
instances
to whether
[that]
of "multiplicity
concept constitutes
the
very
"the
that
or
of power
(not a specific rule but in the premises of the catalog, p. 163). Strength effect, rules.
does
not
Nevertheless,
the
association,
have
an Hume's
exact
as
a measure
complement constant-conjunction
of
expresses
Hume's
criteria
between For
course
in Hume's
proof
of
and
inferences of nature
must will
rely not
on
vary.
the Since
it
is
the debate
illuminate
and non-Popperian is no
us,
sounded reasonable epidemiologists?
causation.
Cause-to
effect relations can be inferred from past experience, such
relative
predecessors,3"7
to
reasonable
sound
this conclusion there
whether
a point of view still widely The point is epidemiologists.
criteria would have
Popperian
Hume,
or Hill's
and Hill's of
irrespective
to Hill
known
thinking
likely that Hill's to Hume. Does
of resembling
essence
that,
suggests was
shared by contemporary
associa
connexion"
of
work
Hume's
tion [has] been repeatedly observed by different persons, in different places, circumstances and time?" The coun terpart is Hume's
criteria
causal Hume's
part
(Rule 7). relates
Discussion The strength of the analogy between Hume's
that
assumption there
is no
proof
but the that
causally related events will still be related in the future in
for
368
Epidemiology
September
1991, Volume
2 Number
5
ON THE ORIGIN OF HILL'SCAUSAL CRITERIA
same
the
can
effect
the
ways, never
of an
validity
from
inference
cause
to
be demonstrated.15
Popper has argued against Hume that the scientific community could temporarily consider as valid theories that had resisted repeated tests. By tests, Popper means can
that
experiments
a matter
As
anyone.16
be
principle?by
reproduced?in
of
is historical
there
fact,
is Newton's
laws
evidence
Epidemiologists are
ments
of motion.17
may
agree with to
tools
important
that experi
Popper
identify
causal
Lind
laws.
was a pioneer of the experimental method.18 Textbooks of refer to Lind, Louis,19 and so on20 to epidemiology roots of experiments in epidemio historical the highlight can hardly share research. But, logic epidemiologists theories are thesis that testable central only Popper's deals with
scientific.21 Epidemiology human
and
populations
the characteristics is more
therefore
an
of
observa
tional than an experimental discipline.13 Epidemiologists often have to infer causation without being able to bring objective
For
proofs. was
connection to controlled
the
example,
elucidated
although
it was
not
amenable
experimentation.
I suggest that Popper's philosophy appears too restric tive for epidemiologists because it does not recognize the scientific character of theories that do not have potential experimental proof. Hume's philosophy that proofs are elusive
is also
by most
rejected
scientists,
contemporary
proof is not available, pragmatic epidemiolo gists simply acknowledge that there is yet no alternative
but when to the
causal
criteria
inferring causation, ties
and
rule
out
logic
that
says,
in substance:
before
it is imperative to check for illogicali
gross
contradictions
between
what
has
found and what we think we know. Hence, the as to Hume's and of Hill's, analogy Popper's, opposed
been
logic.
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Epidemiology
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2 Number
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the methodology Some diseases.
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