"Differences in forage quality parameters of the selected
monocot and dicot species between gabbroic soil and
granitic soil were analysed with a Wilcoxon paired-sample
test as assumptions of normality were violated."

http://edepot.wur.nl/188905

"If the population from which paired differences to be analyzed by a Wilcoxon signed rank test were sampled violate one or more of the signed rank test assumptions, the results of the analysis may be incorrect or misleading. For example, if the assumption of independence for the paired differences is violated, then the Wilcoxon signed rank test is simply not appropriate."

http://www.basic.northwestern.edu/statguidefiles/srank_paire...

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Note added at 55 mins (2013-06-03 17:50:01 GMT)
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"Una vez se han introducido los datos en el Editor de datos, antes de ejecutar el procedimiento para realizar el ANOVA, es conveniente comprobar si los datos que tenemos cumplen los supuestos de Normalidad y Homocedasticidad (el procedimiento ANOVA para medidas repetidas del SPSS no tiene la opción de comprobar este supuesto, sólo lo hace para ANOVA con grupos aleatorios)."

http://www.ual.es/personal/jmllopis/files/CURSO_SPSS_Tercera...