August 2003  

Vol. 5, No. 8


Quality Quiz

Ben N. Jayle is quality manager for Catch & Cuff, a manufacturing firm that supplies restraining devices, including handcuffs, to the law enforcement and public safety industry. Ben has an intuitive, experiential understanding of all the parts that his firm manufactures and assembles. For entertainment in the break room, he often demonstrates his ability to disassemble and reconstruct a pair of handcuffs in record time. He loves his company's product.

Occasionally, when he playfully puts the handcuffs on the stuffed bear mascot decorating his office, he finds that the key does not immediately open the locked pair (at which point he resorts to his intuitive, experiential understanding, and pops them open using other methods). His newfound interest in statistics leads him to create a scattergram to demonstrate the relationship between the lock defect and ambient temperature in the plant. He would like to pursue the statistical application further, and run a regression analysis on line #3 where the lock is assembled. Admittedly, regression is not the strongest card in his statistical hand. He creates the following chart:

The regression analysis seems to suggest support for his theory that temperature does indeed affect the number of defects produced on the line. Ben N. Jayle is ready to create a dramatic PowerPoint presentation for his plant manager as part of a request for air conditioning for the line 3 area, which coincidentally includes his office.

Plant manager Sue Veneer studies the presentation carefully, and asks Ben about the t value of 8.97. Ben knows a lot about his product, but his statistical background is somewhat skimpy—a fact that he does not want to reveal. He understands probability theory enough to know, however, that his chances in guessing correctly are 50-50. The t value either supports or refutes his theory. His response is that the t value demonstrates beyond a doubt that his theory is correct, and that higher temperatures create greater numbers of defects in the lock assembly.

Did Ben N. Jayle get lucky and guess correctly?

A) No

B) Yes


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