I'using a dataset where a sample of 7 subjects edited 2 texts (as in corrected grammar issues, etc.). There were two conditions in the experiments related to the text correction software interface (P and PIO) -- I'm not interested in these conditions. All subjects saw all texts, but the combination condition x text varied -- see screenshot of the study design below. I'm interested in a general view of how measures relating to subjects' behaviour (time spent on correction, number of editing operations, etc. - there will be a few of these) correlate with each other. I'm thinking of doing a by-item PCA (items being sentences in each text, which are many) and doing a biplot with the first two PCs just to illustrate how close to each other different measures are. Would that be my best option? Would it be a problem doing a by-item PCA (i.e. using the average of all subjects per sentence) when the combination condition x text varied between subjects? The odd number of subjects means that there will be one combination which is more frequent. Should I maybe exclude one subject to guarantee that the comparison between the measures I'm interested in is based on the same number of text x condition combinations?