Product or service quality is often defined as fitness for use. This means the product or service meets the customer’s needs. Generally speaking, fitness for use is based on five quality characteristics: technological (e.g., strength, hardness), psychological (taste, beauty), time-oriented (reliability), contractual (guarantee provisions), and ethical (courtesy, honesty). The quality of a service may involve all these characteristics, while the quality of a manufactured product generally depends on technological and time-oriented characteristics (Schroeder, Operations Management, 2008). After a barrage of customer complaints about poor quality, a manufacturer of gasoline filters for cars had its quality inspectors sample 600 filters—200 per work shift—and check for defects. The data in the table resulted.

a. Do the data indicate that the quality of the filters being produced may be related to the shift producing the filter? Test using α = .05.

b. Estimate the proportion of defective filters produced by the first shift. Use a 95% confidence interval.

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Shift First Second Third Defectives Produced 25 35 80