Process design

Comparing traditional approaches to experimental design

The traditional approach taken to develop a new process is One Factor at a Time (OFAT) (Figure 1).  Experimental design on the other hand is a structured set of tests of a process to investigate potentially significant factors that helps to establish cause and effect relationship on the output (Figure 2)  The advantages and disadvantages of both approaches are discussed in Table 1 and Table 2 below.

Figure 1: One Factor at a Time (OFAT) approach
Figure 2: Experimental Deisgn (DoE) approach

Table 1: Advantages and disadvantages of the OFAT approach



Widely taught

Limited coverage of the experimental space


May miss the optimal solution


Fails to identify interactions


Inefficient use of resources

Table 2: Advantages and disadvantages of the DoE approach



Systematic: Thorough coverage of experimental “space”

Minimum entry of ca. 10 experiments

Efficient: Able to establish solution with minimal resource

You may have to run experiments that you anticipate will “fail”