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You can either calculate a Cohen's D in the usual way, or you can convert the F statistic to some sort of effect size (which is covered, I think, in Andy Field's "Discovering Statistics..." books). Also, while I'm here, it's very unlikely you should really be using a one tailed test. A one tailed test means a result in the opposite direction to that which you expect is theoretically and substantively meaningless, and the actions you take as a result will be the same as if you found no effect at all. If that's not true, when you use a one-tailed test, you're just lying about your p-value. (I know that sounds harsh, but I do a LOT of statistical reviews, and if you put a one tailed test in a paper I review, you will be told to revise it.) Jeremy On 5 March 2013 07:50, Michael Puniskis <[log in to unmask]> wrote: > Hi Everyone > > I have a question about reporting effect size but am finding it difficult to get a clear answer from a lot of sources I have read online. Basically I was wondering if it is statistically correct to report either Cohen's d or Pearson's r effect sizes from a within-subjects design with data analysed through a one-tailed paired t-test. > > The data itself is collected through pre and post questionnaires for a social work intervention. In our evaluation reports we report the percentage change between pre- and post-test means, however I would also like to report this in a more scientific way through effect size if possible. > > In hours of online research I've only found very few sources to say this is possible (or at least to specifically say so), as the majority of information I find seems to say effect sizes can only be reported when you have a between-subjects design, for example with a treatment and control group. > > Any information would be greatly appreciated, thanks in advance. > > Mike > > > > --------------------------------------------------------------------------- > > > Please note that Middlesex University's preferred way of receiving all correspondence is via email in line with our Environmental Policy. All incoming post to Middlesex University is opened and scanned by our digital document handler, CDS, and then emailed to the recipient. > > If you do not want your correspondence to Middlesex University processed in this way please email the recipient directly. Parcels, couriered items and recorded delivery items will not be opened or scanned by CDS. There are items which are "exceptions" which will be opened by CDS but will not be scanned a full list of these can be obtained by contacting the University.