Given that your dataset name is "Thesis.data", you will have written, or soon will be writing, a Methods section that describes your experiment. If you are willing to share, that would be useful and would contain the information we need.
This is what I am guessing about your experimental design:
Apparently you have subjects. Subjects is a random effects factor. Each subject has a single value of ICC, BMI, and IDD, which are fixed effects factors.
Each subject is "subdivided" into two sub-units; sub-units are nested within subject. Sub-units is a random effects factor. One sub-unit is assigned to one level of SOURCE. SOURCE is a fixed effects factor.
Each sub-unit is "subdivided" into three sub-sub-units; sub-sub-units are nested with sub-unit. Sub-sub-units is a random effects factor. One sub-sub-unit is assigned to one level of CPG. CPG is a fixed effects factor.
CPG is nested within SOURCE only if the three levels of CPG for SOURCE=1 are different than the three levels of CPG for SOURCE=2. If you have only 3 levels of CPG and these 3 levels are used with both SOURCE =1 and =2, then CPG is crossed with SOURCE. If these concepts of "nested" and "crossed" are unfamiliar to you, then you need to study the resources I suggested. Another good resource is Analysis of Messy Data Volume 1: Designed Experiments, Second Edition. Once you've done that, feel free to post code if you would still like feedback.
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