I am studying the tend of a parameter (VarX) along the differents seasons. I have collected the data from multiple studies and know I am re-analyzing all data together. To take this into accoutn I have put ID_study as random factor. As I have repeated measures from a same population, so I have nested Month with Season in the model; in addittion to put Population as Random factor. As I have data from multiples species I have nested de Family-Genus-Species in other random factor. proc glimmix data=data method=laplace plots=(ResidualPanel(conditional marginal)); class Season Species Genus Family Poblacion ID_study Month; model VarX = Season Month (Season) /dist=beta; random intercept / subject = Poblacion (ID_study); random intercept / subject= Species (Genus*Family); nloptions maxiter=150; lsmeans Season/cl diff PLOT=diff (NOabs center) adjust=tukey; lsmeans Season/cl ilink; run; When I put only the seasons (without the Months) I have four columns in the marginal residuals, and they are also plotted in a downward trend. So I don't know whether SAS plots it in an default way from higher residual values to lower residual values (so the downward trend is an artefact) or whether it is the real order of the months. I have put the Months like: Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, Dec. At the beginning I though that maybe it were plotted alphabetically, but the proximity of the columns do not correspond with it.
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