An industrial engineer conjectures that a major difference between successful and unsucc...

An industrial engineer conjectures that a major difference between successful and unsuccessful companies is the percentage of their manufactured products returned because of defectives. In a study to evaluate this conjecture, the engineer surveyed the quality control departments of 50 successful companies (identified by the annual profit statement) and 50 unsuccessful companies. The companies in the study all produced products of a similar nature and cost.The percentage of the total output returned by customers in the previous year is summarized in the following graphs and tables.

a. Do the data provide sufficient evidence that successful companies have a lower percentage of their products returned by customers? Use α = .05.

b. Was the pooled t test or the separate-variance t test used in the computer output?

c. Do the required conditions to use the test in (a) appear to be valid for this study? Justify your answer.

d. How large is the difference between the percentage of returns for successful and unsuccessful companies?