An experiment was run in a wave soldering process. There are five controllable variables and three noise variables. The response variable is the number of solder defects per million opportunities. The experimental design employed was the following crossed array
(a) What types of designs were used for the inner and outer arrays? What are the alias relationships in these designs?
(b) Develop models for the mean and variance of solder defects. What set of operating conditions would you recommend?