Please Help With This Question Thank you
Message posted by Mary Ann (via 66.66.54.46) on December 19, 2001 at 9:17 PM (ET)

A senior manager wishes to assess which of two models of steel-belted radials will last longer in terms of mean mileage until ‘wear out’ (tread worn to a certain depth) if used on the entire fleet of company cars.

a.) Consider if a stock boy put tires of type 1 on one set of cars and type 2 on another set of cars, drive the cars until the tires are ‘worn out’ and see which set gets more mean mileage. Cite a major statistical flaw in this proposal.

b.) The senior manager’s proposal is to select 30 cars from the fleet at random and to put one tire of each type on the rear wheels (which side for 1 and which side for 2 is chosen at random for each car). Cars will then be driven normally by 30 different personnel (who do not know the tires are being evaluated). Find a 98% confidence interval for the paired difference md = m1 - m2, where d-bar is 1.6, and Sd is 6.4 (figures in thousands of miles).

c.) Interpret (explain the meaning of) your interval in part b) in terms that relate to the tires’ comparative mean mileage.

READERS RESPOND:
(In chronological order. Most recent at the bottom.)

Re: Please Help With This Question Thank you
Message posted by JG (via 128.8.23.67) on December 20, 2001 at 1:53 AM (ET)

b. -2.4,5.6

c. probably no difference - in we need a bigger sample size such as 185 or more to measure a difference of this size with this error rate