As stated, the experimenter endeavours to control conditions as much as
possible. Ideally they will control them completely. If they can do this they are
justified in arguing that any change in Y is solely due to X.
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If they cannot
control the conditions completely they run the risk that other factors affect the
outcome. These other factors are known as confounding variables because
they confuse the outcome and defeat the purpose of the experiment.
Where external conditions are difficult to control, one method of enhancing
control is to include in the experiment two (or even more) groups. In the case
of two groups, one is actually called the ‘control group,’ while the other is
called the ‘experimental group.’ The control group is, as far as possible, equal
in composition in all respects to the experimental group. The two groups,
however, are treated differently in the experiment. Thus in the experiment
testing the effect of an increase in temperature from 20 degrees, the
temperature for the control group remains at 20 degrees right throughout the
experiment. By contrast, the temperature for the experimental groups starts at
20 degrees but goes through an additional five stages as outlined above.
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A simple and classic illustration of experimental method comes from Galileo
Galilei (1564-1642) the distinguished scientist, mathematician and philosopher.
Galileo was born to science
because his father, Vincenzo Galilei, a music
theorist, had performed experiments on the effect that stretching the string of a
musical instrument had on pitch. By these experiments he established that the
pitch varies according to the square root of the tension.
Galileo is famous for an experiment that may in fact have been apocryphal. It
concerned the velocity of falling objects. Aristotle (384-322) had argued that
heavier objects fell faster than lighter ones and that the velocity of falling
objects was proportionate to their mass or weight. A biography by Galileo's
pupil, Vincenzo Viviani, claims that Galileo actually conducted an experiment
to test Aristotle’s theory. He ascended the Leaning Tower of Pisa
and
dropped balls of similar metallic material but different masses. He observed
that they all fell at the same rate. Thus the time of their descent was
independent of their mass.
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This notion of total control of conditions but for the independent variable is
referred to by the Latin tag as ceteris paribus. It means everything else stays the
same or all other things being equal. That is, there are no intervening factors that
provide an alternative explanation for what has occurred.
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To ensure better control, the second batch of mental arithmetic questions
should be of similar difficulty to the first.
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