Consider Exercise 15.11. Suppose there was some experimental difficulty in making the runs. In fact, the total experiment had to be halted after only 4 runs. As a result, the abbreviated experiment is given by with only these runs we have the signs for contrasts given by Comment. In your comments, determine whether or not the: contrasts are orthogonal. Which are and which are not? Are main effects orthogonal to each other? In this abbreviated experiment (entitled a fractional factorial) can we study interactions independent of main effects? Is it a useful experiment if we are convinced that interactions are negligible?Explain.

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