= Residuals and Non-normality = This page will give some tips on aspects of looking at residuals in order to assess non-normality. In particular it will stress how * in repeated measures data, the thing that matters is the distributions of differences between pairs of measures (or more general contrasts in the repeated measures). * in grouped data, it is the residuals adjusted for group means that matter Consider this very small example: || '''X1''' ||<50%>'''X2'''|| || 1 || 2 || || 2 || 1 || || 3 || 2 || || 1001 || 1002 || The distributions of the variables are very skewed. The distribution of the differences (for a repeated measures t-test) are at least symmetrical, if not normal. [Last updated on 21 September, 2010] ---- [[FAQ|Return to Statistics FAQ page]] [[CbuStatistics|Return to Statistics main page]] [[http://www.mrc-cbu.cam.ac.uk/|Return to CBU main page]] These pages are maintained by [[mailto:ian.nimmo-smith@mrc-cbu.cam.ac.uk|Ian Nimmo-Smith]] and [[mailto:peter.watson@mrc-cbu.cam.ac.uk|Peter Watson]]