Asking the Right Questions, A Guide to Critical Thinking, 8th Ed

Pra cti ce an d Revi ew 201
What is the source of this research? How many times have these kinds of studies
been replicated? How many individuals in these studies were tested? Were
the tests of mental acuity given to a random sample, involving individuals of
various backgrounds, ages, health conditions, etc.? Without a more detailed
description of the cited brain research, such research cannot be considered as
helpful evidence.
Similarly, the author's appeal to expert testimony in the fourth reason as
evidence that exercise reduces stress and anxiety suffers from a lack of important
information. The author provides no reference to the study or how
frequently these kinds of studies have been replicated. In addition, the author
does not describe the ways in which the studies were conducted. Consider, for
example, the possible differences in results from experts' testing the stress
levels of a group of retirees in one study from parents who have multiple jobs
in another study.
Are There Rival Causes?
Support for the fifth reason is based on the association between exercise and
obesity, implying that a lack of the former causes the latter. But correlation
does not prove causation! Rival causes can explain the relationship. For
example, individuals who have a very low metabolism are more likely to be
obese, regardless of their level of physical activity. Genetics could pre-dispose
certain individuals to be obese, even though these individuals might exercise
regularly.
Are the Statistics Deceptive?
Some of the statistics deceive us by proving one thing while concluding
another. For example, the author of the passage describes the number of
individuals who do not exercise regularly. The statistic that 3 out of 10 people
exercise regularly, however, proves only that of those people surveyed 3 out of
10 exercise regularly. It certainly does not prove that 7 out of 10 also have a
poor diet and are at a higher risk for developing life-threatening diseases. In
fact, the statistic tells us nothing about dieting or risk of developing diseases.
Also, the statistic that people who maintain a high-fiber diet could slow
prostate cell growth by 30% is obviously meant to illustrate one particular benefit
of a high-fiber diet. But this statistic in its strongest form proves only that
individuals who consume high amounts of fiber could slow the growth of