I believe that this necessary statistical procedure is effect size analysis, and without it, I believe that we fail to tell the truth, the whole truth, and nothing but the truth when describing our neuropsychological research.
In the MRPP procedure, the effect size of the difference between distributions is given by a disparity statistic (K), which takes into account differences in group centroids, variances, skewness, kurtosis and shape [53].
Meta analysis studies show that this counterbalancing procedure increases effect sizes for a CPP [ 7].
Information regarding study recruitment, acceptability of study processes and measures, and data quality would allow refinement of the evaluation procedures and effect sizes to be calculated and used for power calculations to establish the necessary numbers for a fully powered RCT.
Using meta-analytic procedures a pooled effect size then is calculated.
However, as such a study has yet to be carried out within a UK-context, it was considered essential to first conduct a pilot trial, to assess feasibility of procedures and likely effect size within this setting.
Duvall and Tweedie trim and fill procedure resulted in an effect size of d = 0.88 (95% CI = 0.68-1.09; number of imputed studies: 2), which suggesting that the results of the study were not significantly altered after adjusting for the publication bias.
A recent re-analysis of these data classifying studies into those that tried to maximize placebo effects and into trials that used placebo only as a control procedure found a large effect size of d =.95 for studies maximizing placebo effects, which was significantly different from studies using placebo as control (d =.15) [ 12].
A multilevel model that is appropriate when several subjects are available is integrated into the Bayesian procedure to provide a standardized effect size measure comparable to effect size measures in a between-subjects design.
(χ2 tests with more than one degree of freedom are unfocused omnibus tests, and require a much more complicated procedure for conversion to an effect size; see [13], [14], [15] for details).
