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The sample attributes are:
- organism part
The experimental variables are "disease", "compound" and "dose", as they differ between the samples and are the subject of the study (investigating the effect of the compound on the disease state).
"Age" also differs between the samples, and it's clear that pigs with induced injury are older than the healthy controls. However, the point of the experiment was not about comparing older vs. younger pigs, hence "age" is not declared as experimental variable. "Compound" and "dose" were not listed as a sample attribute as they are not intrinsic properties of the pigs or the synovial membranes.