We experience the world in
a time-oriented manner through cause and effect. First Lucy
that white berry, then she became sick. First I hit Bob's foot
with a hammer, then his foot swelled with a purple bruise.
that eating the white berry is what actually made Lucy sick later.
I conclude that being hit with a hammer is what later caused
foot to swell. It is logical enough on the surface. Often, it
seems clear--absolutely clear--that a specific action caused
event to happen. This is what is known as causation.
Many events appear to be the results brought about by identifiable
causes, and the human mind is geared to look for these cause/effect
We get into trouble
when the mind seeks or creates an artificial cause/effect relationship
that doesn't actually exist. After something especially beneficial
or harmful occurs, we want to know what caused it. We tend to
focus on the first action we noticed before the effect,
then assume that it must have been the catalyst triggering the
later event. Nine times out of ten, we're right. It was the white
berry that made Lucy sick. It was true that hitting a foot with
a hammer makes that foot swell and bruise. That makes us lazy
intellectually; we forget that, one time out of ten, we pick the
wrong cause. In Latin, this type of logical mistake is called
hoc ergo propter hoc fallacy, which means "After
this, therefore because of this." It's the idea that any
event which happened first must be the particular event
that caused a good or bad event later, and once we find a possible
answer we tend to snatch hold of it and then stop thinking about
For example, suppose the fall
term of classes ends in December. The manager of a toystore in
the local mall hires one new worker. This worker is a college
student named Stacy. She wants to do some work before spring term
classes start. After Stacy is hired, the store's sales shoot up
by 300%. "Wow!" the manager says to herself,
"That Stacy is a fantastic sales worker! I haven't hired
anyone else but Stacy. Still, since we hired her, our sales have
tripled! I'd better give her a raise!" Is the manager's conclusion
logical? Is it true that Stacy must be fantastic at her job?
Odds are, nine out of ten
readers at this point are nodding, thinking to themselves, "Yeah,
it makes sense to me. You hire a new girl, and the sales go up.
No other girls were hired. It must be the new girl's work."
On the other hand, the
tenth reader stopped and thought, "Wait a minute.... Didn't
you say Stacy was hired in December? That's right around
Christmas time. Maybe the reason the sales went up wasn't because
of Stacy, but because of the time of year." The manager's
conclusion now vanishes in a puff of logic.
Which one were you? If you
spotted the logical fallacy, puff out your chest and strut around
in pride as an intellectual champion. You were clear-headed and
avoided the post hoc error. If you didn't spot the problem,
and made the same assumptions the manager did, don't feel too
ashamed. Often causation is trickier than it looks.
The problem is that correlation
is different from causation. Correlation
is when two or more things or events tend to occur at about the
same time and might be associated with each other, but aren't
necessarily connected by a cause/effect relationship. For instance,
in sick people, a runny nose and a sore throat correlate to each
other--they tend to show up in the same patients. That doesn't
mean runny noses cause sore throats, or that sore throats cause
runny noses, however. Forgetting that leads to sloppy thinking.
Proud journalists point out
that, in the last hundred years,
no peaceful nation with a free press has ever experienced severe
famine. They argue that freedom of the press prevents blunders
in governmental policy and it allows more efficient advertising
and dispersal of commodities like food. But is that true? On the
other hand, no country with a tradition of honest, publically
monitored elections has ever experienced massive famine in the
last hundred years either--at least not in times of peace. Which
factor "caused" the surplus agriculture and trade to
prevent the fearsome famine? Was it free speech or free elections?
Arguably, neither caused
it. Perhaps it's all accidental. Free speech or elections
no effect on agricultural output. Or have we got our cause and
effect backward? Did having sufficient food ensure a stable
society so that free speech and democracy could blossom in the
first place? Perhaps in famished lands, free speech and free
fall by the wayside during and after the famine, and thus these
hungry countries tend to slide into repressive dictatorships.
If that's true, then repressive dictatorships might not actually
bring famines upon themselves through clumsy management or
of advertising, as earlier suggested.
This is not just a moot intellectual
point. Public policy often hinges on spending money to bring about
a specific effect. For instance, consider New York City in the
1980s. The city at that time was a dangerous place. Crime was
at an all-time high then. Murders, prostitution, and drug-dealing
had reached epic levels. New York had tried stiffer penalties,
longer jail terms, mandatory counseling, methadone treatments,
and a variety of other approaches without denting the ugly problem.
Mayor Guiliani hired researchers to come in. What was one of the
early findings? Analysts spotted a correlation between graffiti
in an inner-city neighborhood and the relative crime-rate in that
area. The more graffiti, the higher the crime rate. Treating this
as a cause/effect relationship, New York's mayor Guiliani decided
to alter the funding for the police department, cutting back money
for some types of law-enforcement, pouring money into an city-wide
anti-graffiti campaign, and arguing that a cleaner city would
diminish the visual "mindset" of crime in the area.
He enacted a zero-tolerance policy by prosecuting taggers who
painted on public property, and he cleaned up Times Square and
the trashiest parts of the city. As overall crime rates dropped
in the 1990s, the mayor touted his program as a success.
Impressed and surprised, other
cities tried to duplicate New York's approach.
They enacted similar financial policies and created similar laws.
They hauled in hoodlums and cleaned up graffiti . . . and
they all failed miserably. Crime in these cities either remained
the same or in one or two cases, worsened slightly, even though
the changes they made were nearly identical to that of New York.
What happened? Why couldn't
they duplicate New York's success? The problem may be one
causation. That correlation between the amount of graffiti and
the overall crime rate doesn't necessarily mean that graffiti
causes crime to happen--no more than the correlation
between black eyes and broken noses in people who lose fist
means that black eyes "cause" broken noses. The crime-rate
in an area also correlates to the rate of unemployment, for
and New York's unemployment was dropping steadily through the
1990s. Perhaps rising employment caused crime to drop at just
about the same time the mayor started his anti-graffiti campaign.
The rate of drug abuse in a given area also correlates to the
number of crimes in that area. The city had started constructing
larger drug treatment clinics in the late 1980s after the decade's
peak of cocain addiction. Although the construction funding had
been spent in the late 1980s without visible effect, many of
clinics actually started operation only two or three years before
the fall in crime in the early 1990s. Perhaps after two or three
years of treatment, a significant fraction of cured addicts no
longer needed to engage in crime sprees to support an expensive
and illicit habit. It's not at all clear if there was just one
cause--maybe the combination of rising employment, drug clinics,
and the mayor's anti-graffiti campaign together had
a synergistic effect that was missing in other cities where
anti-graffiti program didn't work. One recent book on applied
economic theory, entitled Freakonomics, has gone so
far as to suggest plausibly the source of the crime-drop nationwide
in the late 1990s and the early 2000s has been an unintentional
result or by-product of abortion policies thirty years earlier!
To give a more recent example,
on June 28, 2003 Reuters
News Agency reported on a Hungarian medical study of 221 men
who carried cell phones. The study found that men who carry
phones in the front pockets of their pants rather than in a
jacket or briefcase had a 30% lower sperm count than the average
population as previously measured in 1970. Immediately an outcry
appeared to start lawsuits against cell phone companies for
sterility in men, and some consumer watchdogs called for warning
labels on cell phones.
The problem is that the study
only found correlations--it did not determine clear causation.
As Dr. Hans Evers pointed out, many individuals who carry their
cell phones in their pants pockets rather than their jacket
do so because they are smokers. They carry their cigarette
pack in their jacket pockets instead of a pants pockets--to
avoid crushing their cigarettes--and thus must carry the cellphone
in their pants instead. It has long been known that smokers have
a reduced sperm count. Perhaps smoking caused the lower sperm
count rather than position of the cell phone per se.
Also, the study did not take into account other factors like
levels (stress can also cause a drop in sperm count); perhaps
the men carried cell phones constantly because of a stressful
job in which they needed to stay in contact with a company twenty-four
hours a day. Finally, the overall sperm count of men may have
dropped locally or globally as a whole since the earlier 1970
findings used as a control--possibly due to the increasing levels
of chemical pollution worldwide. (Male alligators in parts of
Florida, for example, also have 30% lower sperm counts than
did in the 1970s, but nobody thinks that's a result of their
cell phone use!)
The point to all this is
that, if you are writing an argument, and you claim a cause-effect
exists, you should double-check and triple-check that it is
causation and not mere correlation. It's hard to nail down causation
conclusively, as evidenced by tobacco company lawyers who argued
for forty years that smoking merely "correlated" to
lung cancer rather than actually caused it. However, the least
you can do is pause and ask yourself what other possible causes
exist in addition to the one you point to in a paper. If they
do exist, you need to think through the evidence and determine
why these other causes are less likely than the one you propose.