I have a question regarding my formula for songbird, which is in the following format

–p-formula “Treatment+DPT+Parasites”

In the Treatment column of my metadata file, I have 4 categories (Treatment groups), C (control), MeOH, F9, and F150. However, the C category is missing from the differentials. I understand that the number of variables reported for the Treatment column should be K-1 or 3 which explains why the C category is missing. I just want to confirm that the C category is the reference? AndTreatment_DPT_Parasites_differentials_pdp02_200k-viz.qzv (1.2 MB) Treatment_DPT_Parasite_qurro_plot_q2.qzv (857.2 KB) , that the intercept is the mean abundance of the microbes in the C category and that the differential values in the MeOH, F9 and F150 columns are the log-fold changes of the microbes compared to the C (reference) category?