On Wed, 7 Mar 2007 16:19:31 -0500, Ryan Earley <[EMAIL PROTECTED]> wrote:
>Help with stubbornly non-normal data.... > >We have a data set with 2 independent variables and 1 dependent (Gosner >stage for amphibian larvae). Hello, Normality is less important. What about homogeneity? We have tried every creative way to transform >the data a waste of your time I am afraid >and end up with significant deviation from normality each time. Just make a histogram or QQ plot, and judge by eye. Normality is not soo important....compared to independence and homogeneity. But it also depends on sample size, whether the data are balanced and how significant your results are. And perhaps your non-normality is caused by an improper model? See also: www.springer.com/0-387-45967-7 for possible solutions. >What we'd like to ultimately do is test both main effects and their testing the main efffects while the interaction is significant??? There is a whole discussion on this topic. See Underwood (200-something). >interaction (which effectively eliminates the use of two Kruskal-Wallis >tests or Friedman's two-way ANOVA). We would be indebted to anyone who might Is your response (dependent) ordinal??? Then I guess it has only a few unqiue values....? No wonder it is not normal. In thas case, have a look at multinomial logistic regression (MLR). There is also an "extension" of MLR that takes into account the fact that the data are ordinal. See: Kleinbaum DG Klein M (2002) Logistic Regression A Self-Learning Text. New York: Springer-Verlag Alain Dr. Alain F. Zuur First author of: Analysing Ecological Data (2007). Zuur, AF, Ieno, EN and Smith, GM. Springer. 680 p. URL: www.springer.com/0-387-45967-7 Analysing Ecological data using GLMM and GAMM in R. (2008). Zuur, AF, Ieno, EN, Walker, N and Smith, GM Springer. Other books: http://www.brodgar.com/books.htm Statistical consultancy, courses, data analysis and software Highland Statistics Ltd. 6 Laverock road UK - AB41 6FN Newburgh Tel: 0044 1358 788177 Email: [EMAIL PROTECTED] URL: www.highstat.com URL: www.brodgar.com >have a suggestion on how to proceed statistically. Thanks for your help in >advance. > >Best, >Ryan L. Earley & Foung Vang >Cal State Fresno >=========================================================================
