Indicate what would be the relevant population and the most appropriate sampling design. Be sure to give the reasons for your answers.

Scenario

The McArthur Company produces special vacuum cleaners for conveniently cleaning the inside of cars. About a thousand of these, with stamped serial numbers, are produced every month and stored serially in a stockroom.

Once a month an inspector does a quality control check on 50 of these. When he certifies them as to quality, all 1000 units are released from the stockroom for sale. The production and sales managers, however, are not satisfied with the quality control check since, quite often, many of the units sold are returned by customers because of various types of defects.

State the relevant population and the most appropriate sampling design for selecting the 50 units. Be sure to discuss the reasons for your answers.