Abstract
The place of taking measures on a dependent variable before
treatment, hereafter labeled pretesting, in any type of research is
described.
It is particularly issues when behavior of the patients or subjects is a
key interest. Pretests decrease the #internalvalidity of experiments
(i. e.,
render them incapable of completely proving what they are intended to
prove). The loss of internal validity may be great in some cases, and
little
or no loss in others, but just how much has been lost cannot be proven.
Pretests are sometimes credited with demonstrating that #randomization
has produced reasonably equivalent groups, but that is indexed by p,
with equal accuracy whether or not pretests are employed. There are
usually many sources of differences between subjects which could result
in different outcomes on the dependent variable(s). The only valid
index of whether an initial inequality of groups has produced a spurious
result is p.
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To Pretest or Not to Pretest by Robert Pasnak in BJSTR
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