A missing value in a 2k factorial. It is not unusual to find that one of the observations in a 2k design is missing due to faulty measuring equipment, a spoiled test, or some other reason. If the design is replicated n times (n > 1), some of the techniques discussed in Chapter 5 can be employed. However, for an unreplicated factorial (n = 1) some other method must be used. One logical approach is to estimate the missing value with a number that makes the highest order interaction contrast zero. Apply this technique to the experiment in Example 6.2 assuming that run ab is missing. Compare the results with the results of Example 6.2.