I'm looking for some help nesting factors.   I have the following experiment design:   Four Treatments Four pens per treatment Four sampled animals per pen 3 samples measured per animal, sometimes just two samples measured, at the same time point.   Previously, I have only take one sample per animal, and my mode and random statement with nesting looks something like   Model = Treatment / cl; Random Pen(Treatment);   I'm wondering how I could work Animal into that statement.  Maybe Animal*Pen(Treatment), or Animal (Pen Treatment) ?   Furthermore, when I write out a linear model equation, I would represent the Pen(Treatment) as uij   u for random effect of j pen for i treatment   How would I properly state it if I incorporated Animal?   uija, with a for animal maybe?   I look forward to any thoughts on this would be appreciated.  Apologies if my stats language is a bit imprecise.  Too much veterinary medicine and not enough math in my life. ... View more