Fig. 2.

Factor estimation from the between-run ratio matrix. (A) Each cell in the between-run ratio matrix is the geometric mean of all ratios that can be calculated between observations in the same conditions from each pair of runs and is an estimate of the column and row run factors. Runs 5 and 6 have no conditions in common (Fig. 1) and the F6/F5 ratio is missing. (B) Divide each ratio in a column by the ratio in the column with the missing ratio and take the geometric mean to obtain a fold-difference between the columns. (C) Divide each observed ratio in the row of the missing ratio by the fold difference in (B) to obtain an estimate of the missing ratio. The geometric mean of these estimates completes the between-run ratio matrix (D). (E) Because in each column of this completed matrix the denominator in the ratio is a different run factor, these factors cancel out in the geometric mean of a column of ratios, resulting in the run factor (Eq. (4)).