A lot of people use the term "critical thinking" in an offhand way. Usually
the writer who uses this term is trying to imply that anyone who disagrees
with the writer's theory or belief is naive. Critical thinking is also
produced as an excuse to attack a particular theory or to promote "equal
time" for a competing belief.
Critical thinking, however, is much more complex than this. It involves
more than just fault finding. After all, no theory is perfect and unflawed.
Rather it looks at the evidence supporting a theory in addition to the
critical evidence. It evaluates the quality of these arguments rather than
the quantity. Nit pickers will always find hundreds of little things to
complain about, but a critical thinker will brush aside trivial concerns
about a theory if other supporting evidence for that theory is strong.
A perfect example of critical thinking versus nit picking is the developing
recognition in the 1950s and 1960s that cigarette smoking causes cancer. This
body of research is summarized well in Gail 1996. The research studies that
identified a link between smoking and cancer were not perfect. You couldn't
use randomized trials and you couldn't use blinding and you couldn't use a
host of other research methods that would make these studies more rigorous.
There were animal studies, but the nitpickers pointed out that you can't
always extrapolate from animals to humans. There were far higher rates of
smoking in cancer patients than among controls, but the nitpickers pointed
out that these were retrospective studies and people didn't always remember
things accurately or report them truthfully. Prospective studies were
harder to do, but when these also showed a link between smoking and cancer,
the nitpickers had another counterargument. They pointed out that people who
smoke also tend to have other vices and bad habits that might account for the
differences seen.
A critical thinker would look past the individual nitpicks, though. A
critical thinker subjects the objections to a theory or belief to the same
level of scrutiny as the theory or belief itself. The problem with the
nitpickers, of course, is that each time a different type of study came out
that showed a link between smoking and cancer, they had to come up with yet
another explanation. And all of these alternate explanations had to be true
simultaneously in order to negate the growing body of evidence. It becomes a
house of cards that eventually collapses under its own weight.
One of the more fascinating episodes in this history was an alternate
theory proposed by the nitpickers. The theory was that it wasn't the smoking
that caused cancer, but rather the cancer that caused smoking. This seems
like a bizarre claim, since the smoking often precedes the cancer by several
decades. The explanation offered was the certain people have a genetic makeup
that makes them more vulnerable to cancer. The same genes that make a person
cancer prone might also make a person more susceptible to nicotine addiction.
A critical thinker would have to carefully examine this claim. It's true
that in many situations, you can't easily identify whether A causes B or B
causes A. For example, there is a fair amount of research that seems to
indicate that an optimistic and hopeful attitude is associated with better
outcomes when facing a serious illness or disease. Does this positive outlook
cause these people to have a stronger immune system that allows them to
better battle the disease? Or is it possible that the disease itself is less
virulent in certain people, possibly in ways that are difficult to measure
directly. Perhaps these people with the less virulent disease know something
that the doctors don't and it manifests itself as a more positive attitude.
So maybe it is prognosis of the disease itself that causes the differing
attitudes and outlooks rather than the attitudes and outlooks affecting the
prognosis of the disease.
With cancer and smoking, however, a critical thinker can easily identify
which is the cause. If it were true that a genetic predisposition to cancer
were associated with a genetic predisposition to addictability, then these
cancer genes would operate the same way in countries where cigarettes were
easily available as in countries where cigarettes were hard to come by.
That's not really the case, though. In China, cigarettes came into widespread
use much later than in Europe and America. The late surge in lung cancer
cases in China that followed the wide distribution of cigarettes contradicts
the hypothesis that it is the genes rather than the cigarettes.
Keep in mind that contrasting the rates of smoking and cancer in different
countries is, by itself, a rather weak form of evidence. There are many
obvious and subtle differences between China and America. The value of the
data on smoking and cancer in China, however, is that it is grossly
inconsistent with the belief that cancer causes smoking. To maintain this
belief, you would have to postulate that a mutation occurred in the genes of
most Chinese people right around the time that cigarettes were widely
adopted.
In summary, it's not so much that the belief that smoking causes cancer is
based on perfect and unflawed data, but rather that the flaws are trivial
compared to the flaws in the arguments of those who believe in alternative
explanations.
