The two-factor factorial design is the most elementary of all factorial designs. In this section, the concepts developed for the two-factor 22 design in Section 8.2 are extended to the more general factorial design that has three or more factors. With this design, there are 2k treatment combinations, where k = the number of factors (CTPs or Xs); for example, 23 = 2 × 2 × 2 = 8 treatment combinations. Table 8.7 extends the format of Table 8.6 to the 23 design in standard order. Standard order is an arrangement for listing trials in which the first factor alternates between – and +, the second factor alternates between –,– and +,+, the third factor alternates between –,–,–,– and +,+,+,+, and so on.