Advantages of Within-Subject Designs (1 of 2)
Subjects inevitably differ from one another. In an experiment on
children's memory, some children will remember more than others; in
an experiment on depression, some subjects will be more depressed
than others; in an experiment on weight control, some subjects will
be heavier than others. It is simply a fact of life that subjects
differ greatly. In
between-subject
designs, these differences among subjects are uncontrolled and
are treated as
error. In within-subject
designs, the same subjects are tested in each condition. Therefore,
differences among subjects can be measured and separated from error.
For example, consider the following data:
Control Experimental
Subject condition condition
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Subject 1 12 14
Subject 2 25 28
Subject 3 29 32
Subject 4 54 57
Every subject did better in the experimental condition than in the
control condition. Even though the advantage of the experimental
condition is small, it is very likely real since it is very
consistent across the four subjects.