Abstract

A
 central 
issue
 confronting
 both 
philosophers
 and 
practitioners 
in
 formulating 
an 
analysis 
of 
causation
 is the
 question
 of
 what
 constitutes
 evidence
 for
 a
 causal
 association.
 From
 the
 1950s
 onward,
 the biostatistician
 Jerome
 Cornfield
 put
 himself
 at
 the
 center
 of
 a controversial
 debate
 over
 whether cigarette
 smoking
 was
 a
 causative
 factor
 in
 the
 incidence
 of
 lung
 cancer.
 Despite
 criticisms
 from
 distinguished
 statisticians
 such
 as
 Fisher,
 Berkson
 and
 Neyman,
 Cornfield
 argued
 that
 a
 review
 of
 the scientific
 evidence
 supported
 the
 conclusion
 of
 a
 causal
 association.
 Cornfield's
 odds
 ratio
 in
 case‐control
 studies — as
 a
 good
 estimate
 of
 relative
 risk — together
 with
 his
 argument
 of
 ''explanatory
 common
cause'' 
became 
important 
tools
 to 
use 
in
 confronting 
the 
skeptics.
 In
this
 paper,
I 
revisit 
this important 
historical 
episode 
as 
recorded 
in
 the
Journal 
of 
National 
Cancer 
Institute 
and 
the 
Journal 
of the 
American Statistical 
Association. 
More 
specifically,
 I
 examine 
Cornfield's 
necessary
condition 
on 
the minimum
 magnitudes 
of 
relative 
risk 
in 
light 
of
confounders.
 This 
episode 
yields 
important 
insight 
into the
 nature
 of
 causal
 inference
 by
 showing
 the
 sorts
 of
 evidence
 appealed
 to
 by practitioners
 in supporting
 claims
 of
 causal
 association.
 I
 discuss
 this
 event
 in
 light
 of
 the
 manipulationist
 account
 of causation.