Editor: CombiStat let you carry out two useful statistical procedures. Firstly, you can combine several MeanĀ±SEM values into an overall MeanĀ±SEM. Secondly, you can calculate the SEM and SD of the ratio (X/Y), product (X*Y), difference (X-Y) and sum (X+Y) of the mean values, X and Y, of two independent variables, x and y, both with an associated SEM. CombiStat runs on any Macintosh with any system from 7.6 to 9.2 and can be downloaded as a binhex file by clicking here. CombiStatX runs under Mac OSX and can be downloaded as a zipped file by clicking here. You will need Stuffit Expander or similar utility to expand the files.