Statistics: Signifigance Level

Chapter 11 problems

24. Clark Heter is an industrial engineer at Lyons Products. He would like to determine whether there are more units produced on the afternoon shift than on the day shift. A sample of 54 day-shift workers showed that the mean number of units produced was 345, with a standard deviation of 21. A sample of 60 afternoon-shift workers showed that the mean number of units produced was 351, with a standard deviation of 28 units. At the .05 significance level, is the number of units produced on the afternoon shift larger?

34. A number of minor automobile accidents occur at various high-risk intersections in Teton County despite traffic lights. The Traffic Department claims that a modification in the type of light will reduce these accidents. The county commissioners have agreed to a proposed experiment. Eight intersections were chosen at random, and the lights at those intersections were modified. The numbers of minor accidents during a six-month period before and after the modification were:

Number of Accidents
A B C D E F G H
Before modification 5 7 6 4 8 9 8 10

After modification 3 7 7 0 4 6 8 2

At the .01 significance level is it reasonable to conclude that the modification reduced the number of traffic accidents.

40. The following data on annual rates of return were collected from five stocks listed on the New York Stock Exchange (“the big board”) and the five stocks listed on NASDAQ. Assume the standard population deviations were the same. At the .10 signifigance level, can we conclude that the annual rates of return are higher on the big board?

NYSE NASDAQ
17.16 15.80
17.08 16.28
15.51 16.21
8.43 17.97
25.15 7.77