The Efficacy of Rational
Emotive Therapy: A Quantitative Review of the Outcome
Research. Each comparison of RET to the baseline
assessment, control, or treatment groups was expressed in
terms of the Standardized Difference between Mean Scores
(d; Cohen, 1977). Some researchers (e.g., Glass
1976, 1977; Smith & Glass, 1977; Smith et al, 1980)
advocate using the comparison group standard deviation as
the denominator for d. However, there
are two reasons against using the comparison group standard
deviation, first, the within-subjects standard deviation has
approximately half the sampling error of the comparison
group; second, the within-subjects standard deviation
generally provides a more accurate estimate of the
population s (Hunter et
al, 1982). After d is calculated
for each study, the effect sizes are averaged. Where possible, effect sizes were
obtained by directly calculating d from the means
and standard deviations reported in the individual study.
Otherwise d was calculated from t,
f, r, or a
probability value using procedures taken from Cohen (1977)
or Hunter et al (1982). If the comparison was taken from a
two-way ANOVA, the statistic was first converted to the
eta statistic using an algorithm taken from Hasse
(1983). This correlation coefficient was then converted to
d
using procedures outlined by Cohen (1977) and Hunter et al
(1982). When the exact probability level was
given, this value was converted into a z score and then
converted to a point-biserial correlation. A d was then
estimated using the previously mentioned procedures outlined
by Cohen (1977) and Hunter et al (1982). Unfortunately in
some studies, an exact statistic was not available. An
approximation procedure was used to estimate d. Where
nonparametric statistics or multiple comparison procedures
(e.g., Duncan's Multiple Range test or Newman-Keul's test)
were used, the associated probability value (.05, .01, or
.001) was converted first to a z score and then
to a d statistic using the previously discussed
procedures.
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Method
Results
Discussion
References
Appendix
Effect Size
Estimation