Figure 4.

An alternative experimental design for the sporulation study, represented as a directed graph. The boxes represent RNA samples and the arrows represent microarrays. The tail of an arrow is, say, the “red” dye and the head of an arrow is the “green” dye. Thus, the arrow from the time-0 sample to the half-hour sample means to hybridize an array with red-labeled time-0 mRNA and green-labeled mRNA from the half-hour sample. Such a design has advantages over the plan used by Chu et al. in balance, precision of estimates, and distribution of residuals.