The psychopathology of everyday art: a quantitative Study - World ...

There are few answers to this criticism which do not lead to possible inferential errors,
and it is a question of judgement in using a procedure which is appropriate for the sample
and reflects the classification and variety of variables encompassed.
Wolf 222 describes a method using only the most significant results from each
study, but this technique lends itself to type I error. Rosenthal's 223 adaption of the
Stouffer method, i.e. averaging between significance levels transformed to z-scores to
produce one variable per study, are clearly not appropriate here because the standard
deviations and direction of significance of studies must be similar, and the variables non-
correlated, so that they can be weighted equally 224 . Furthermore, although 4 from 11
studies show a very high effect size aggregated in this way and 3 more show a small to
medium effect, 3 studies did not actually report the large numbers of non-significant
statistics, of which their study mostly consisted, and therefore estimates of p=1 would
probably contribute to artificially low averages resulting in a much too conservative
estimate.
Kulik, Rosenthal and others recommend using separate analyses for each variable,
when each study uses several of the same type of variables. There were two main
problems which made this type of analysis difficult in this study: (1) There were tests
between patients and normal controls and between patients and patient controls; and (2)
there was no way of knowing how similar variables with similar terms, which were
tabulated together, actually were. Few studies contributed variables to most of the
222 Wolf (1986) op.cit. p.46.
223 Rosenthal (1984) op.cit. p.72.
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