13.8 Maxine Makitright, president of Good Parts, Ltd., has asked you to develop a model that predicts the number of defective parts per 8-hour work shift in her factory.

She believes that there are differences among the three daily shifts and among the four raw-material suppliers.

In addition, higher production and a higher number of workers are thought to be related to increased number of defectives. Maxine visits the factory at various times, including all three shifts, to observe operations and to offer operating advice. She has provided you with a list of the shifts that she has visited and wants to know if the number of defectives increases or decreases when she visits the factory.

Prepare a written description of how you would develop a model to estimate and test for the various factors that might influence the number of defective parts produced per shift. Carefully define each coefficient in your model and define the test you would use.

Indicate how you would collect the data and how you would define each variable used in the model. Discuss the interpretations that you would make from your model specification.