Hi Folks, I apologize in advance if this is a newbie question, I'm still relative unfamiliar with SAS and overall I don't have a super strong statistics background. I'm trying to analyze an animal feeding trial that someone else executed. Here is the study description: There are a number of birds, housed in 14 blocks. Each block contains a number of pens, for a total of 120 pens. Each pen contains 6-8 birds (the number is variable, as some may die during the trial). The variables that were measured at each time point were BW (body weight) and FI (cumulative feed intake); these are calculated pen-wise: for BW, all birds in the pen are weighed and the total weight is divided by the number of birds; the same is done for FI. The trial length was 43 days, and measurement were taken at day 0,14,21,28,43 There were 8 treatments: T1 is a control (no disease, no supplements); T2 the birds were challenged with a disease; T3 the birds were challenged and also received a commercial antibiotic; T4 the birds were challenged and received no antibiotic, but instead a supplement at a rate of 0.125 g/ton; T5 is the same as TR4 but the rate was 0.250 g/ton; T6 as above, but rate was 0.5 g/ton; T7 same as above but the rate was 0.75 g/ton; T8 same as above but rate was 1 g/ton. All of the treatments have the same number of PENs I have set up the dataset to be the following way: PEN BLOCK TRT DAY AB CHALLENGE SUPPL VAR VALUE 1 1 T4 0 NO YES 0.125 BW 43 1 1 T4 14 NO YES 0.125 BW 33 ... ... ... ... ... ... ... ... ... 1 1 T4 14 NO YES 0.125 FI 525 Where DAY is the number of days elapsed, AB is whether they're receiving antibiotic or not (only T3 received it), CHALLENGE is whether they were challenged or not (all except T1 were challenged), and SUPPL is the amount of supplement received (0 for T1-T3, increasingly higher for T4-T8). The way I see this, it's a simple linear regression, where I'm trying to model the effect of the supplement overall and by day. I tried running a proc GLM as highlighted below: ods graphics on;
PROC SORT DATA=CHICKS; BY VAR CHALLENGE SUPPL;
PROC GLM DATA=CHICKS PLOTS=DIAGNOSTICS; BY VAR;
CLASS DAY AB CHALLENGE SUPPL;
MODEL VALUE = DAY SUPPL DAY*SUPPL AB CHALLENGE;
LSMEANS DAY SUPPL DAY*SUPPL/PDIFF=all;
RUN;
ods graphics off;
QUIT; However, I don't think this is the best approach, for several reasons: I don't know how to model the RANDOM effect of the block (or if I should at all) I'm not modeling the REPEATED measures (the same birds were measured over time from the same PEN). The time points are unequally spaced, and I think PROC GLM doesn't like that. Is there a better way to do this? Thank you in advance for all your feedback.
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