Hello Norman21, firstly thanks for your attention. I saw your recommendation about survival analysis using Proc Lifetest but unfortunately, that procedure is not that I need. The topic listed is very close to what I need, but do not have the solution yet: https://communities.sas.com/t5/Statistical-Procedures/Using-PROC-NLIN-to-fit-curves-for-dairy-cattle-and-Proc-Gplot-to/m-p/435894/highlight/true#M23006 In my database, after the middle of lactation the numbers of cows decrease. The begin of lactation (day 1) I have 1000 observations (cows) and the end of lactation (day 115) I have only 150 observations. The response variable is milk_production (continuous variable). Some people said that I can not compare the groups, because I have not completed basedata. The solution for that is filter the dataset just for animal that have complete lactation. Using this methodology, I will lose information about 750 cows. My doubt is: Are there another way to solve it?
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