Facility layout and material flowpath design are major factors in the productivity analysis of automated manufacturing systems. Facility layout is concerned with the location arrangement of machines and buffers for workin-process. Flowpath design is concerned with the direction of manufacturing material flows (e.g., unidirectional or bidirectional) (Lee, Lei, and Pinedo, Annals of Operations Research, 1997). A manufacturer of printed circuit boards (PCBs) is interested in evaluating two alternative existing layout and flowpath designs. The output of each design was monitored for eight consecutive working days.

Working Days Design 1 ..............................

1,220 units 1,092 units 1,136 units 1,205 units 1,086 units 1,274 units 1,145 units 1,281 units Design 2 1,273 units 1,363 units 1,342 units 1,471 units 1,299 units 1,457 units 1,263 units 1,368 units

a. Construct a 95% confidence interval for the difference in mean daily output of the two designs.

b. What assumptions must hold to ensure the validity of the confidence interval?

c. Design 2 appears to be superior to Design 1. Is this confirmed by the confidence interval? Explain.