Hi, Please could someone help me defining the most appropriate SAS code (SAS 9.3) for my statistical model. Two groups of 3 animals were involved in a Latin square design comprising two periods of 7 weeks.. During the first period group 1 received treatment 1 and group 2 received treatment 2, and inversely in period 2. During each period, we measured the same parameters on all animals at different days (6 days of measurement within the 7 weeks), to follow the evolution of the parameters within each treatment. I suggest this SAS model: Class animal period treatment day; Model parameter = period treatment day day*treatment day*period day*treatment*period; Repeated day /sub=animal*period type=cs ; Run; And one of my colleagues suggest another model: Class animal period treatment day; Model parameter = period treatment day day*treatment day*period day*treatment*period; Repeated day /sub=animal*period; Random animal animal*period / type = cs; Run; I am not sure if these two models are correct, and which one is the most appropriate. In the model, should I test the period effect and the interactions with the period? I am also asking about the random statement in the model: is it useful or not? Why? The type of covariance structure must appear in the repeated or random statement? I would greatly appreciate any help that you could offer. Many thanks, Pauline
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