52013-03-08 10:17:16localhostconverted to 1.6 markup42013-02-11 14:52:22PeterWatson32013-02-11 14:50:24PeterWatson22013-02-11 14:49:59PeterWatson12013-02-11 14:49:52PeterWatson

If you really want to quote an effect size for the pooled analysis ie comparing all the groups at once then you could estimate z as below (again following Field, 2005): Obtain the one or two-sided p-value for the chi-square for the data from using the Kruskal-Wallis and/or chi-square test (it will have more than one df) Find the z value that has the same one or two-sided p-value as that obtained just now for the chi-square. You can do this using a function in any stats package or in Excel. For example in SPSS: suppose the two-sided p-value of my chi-square from doing either a Kruskal-Wallis or chi-square test is 0.02. Running the below gives a z of 2.326 so for a total sample size of 40 the the effect size = 2.326/sqrt(40)= 0.367. Alternatively you could run this from the gui choosing the 'compute' option. If you are using a one-tailed test and, for example, had a one-sided p=0.01 then we could instead tweak the above and use the below which gives a z=1.645.