vote for him and is overjoyed at his soon-to-be-celebrated victory. Explain carefully why Harvey
should not get too excited until the votes are counted.
A company uses two different models, call them model A and model B, of a machine to produce
electronic locks for hotels. The company has several hundred of each machine in use in its various
factories. The machines are not perfect, and the company would like to phase out of service the one
that produces the most defects in the locks. A random sample of 13 model A machines and 11 model
B machines are tested and the data for the average number of defects per week are given in the
following table.
Dotplots of the data indicate that there are no outliers or strong skewness in the data and that there are
no strong departures from normal. Do these data provide statistically convincing evidence that the
two machines differ in terms of the number of defects produced?
Take another look at the preceding problem. Suppose there were 30 of each model machine that
were sampled. Assuming that the sample means and standard deviations are the same as given in
question 9, how might this have affected the hypothesis test you performed in that question?
- The directors of a large metropolitan airport claim that security procedures are 98% accurate in
detecting banned metal objects that passengers may try to carry onto a plane. The local agency
charged with enforcing security thinks the security procedures are not as good as claimed. A study of
250 passengers showed that screeners missed nine banned carry-on items. What is the P -value for
this test and what conclusion would you draw based on it? - A group of 175 married couples are enrolled in a study to see if women have a stronger reaction than
men to videos that contain violent material. At the conclusion of the study, each couple is given a
questionnaire designed to measure the intensity of their reaction. Higher values indicate a stronger
reaction. The means and standard deviations for all men, all women, and the differences between
husbands and wives are as follows:
Do the data give strong statistical evidence that wives have a stronger reaction to violence in videos
than do their husbands? Assume that σ for the differences is 1.77.
An election is bitterly contested between two rivals. In a poll of 750 potential voters taken 4 weeks
before the election, 420 indicated a preference for candidate Grumpy over candidate Dopey. Two
weeks later, a new poll of 900 randomly selected potential voters found 465 who plan to vote for
Grumpy. Dopey immediately began advertising that support for Grumpy was slipping dramatically