CLARIFYING THE CONCEPTS
1. What are the conditions required for a random variable to be multinomial? (p. 632)
11.1.1
(1) Each independent trial of the experiment has possible outcomes, (2) The th outcome (category) occurs with probability , where , (3)
2. Explain in your own words what is meant by a goodness of fit test. (p. 635)
3. Explain the meaning of the term expected frequency. (Hint: Use the idea of the long-run mean in your answer.) (p. 634)
11.1.3
It is the long-run mean of that random variable after an arbitrarily large number of trials.
4. State the hypotheses for a goodness of fit test. (p. 634)
PRACTICING THE TECHNIQUES
CHECK IT OUT!
To do | Check out | Topic |
---|---|---|
Exercises 5–8 | Example 1 | Identifying a multinomial random variable |
Exercises 9–12 | Example 2 | Finding the expected frequencies |
Exercises 13–18 | Example 3 | Calculating |
Exercises 19–22 | Example 4 |
Goodness of fit test: critical-value method |
Exercises 23–26 | Example 5 |
Goodness of fit test: p-value method |
644
For Exercises 5–8, determine whether the random variable is multinomial.
5. We take a sample of 10 M&M's at random and with replacement and observe the color of each. Let , where the possible values of are green, blue, yellow, orange, red, and brown.
11.1.5
Multinomial
6. We select 5 students from a group of 25 statistics students at random and without replacement, and we define our random variable to be , where the possible values of are freshman, sophomore, junior, and senior.
7. We choose 10 stocks at random and with replacement, and we define our random variable to be . The possible values of are New York Stock Exchange, NASDAQ, London Stock Exchange, and Shenzhen Stock Exchange.
11.1.7
Multinomial
8. We pick 10 stocks at random and with replacement, and we define our random variable to be .
For Exercises 9–12, the alternative hypothesis takes the form
.
9.
11.1.9
(a) , , (b) Conditions are met.
10.
11.
11.1.11
(a) , , , (b) Conditions are not met.
12.
For Exercises 13–18, calculate the value of .
13.
10 | 12 |
12 | 12 |
14 | 12 |
11.1.13
0.667
14.
15 | 10 |
20 | 25 |
25 | 25 |
15.
20 | 25 |
30 | 25 |
40 | 30 |
40 | 50 |
11.1.15
7.333
16.
8 | 6 |
10 | 8 |
7 | 9 |
5 | 7 |
17.
1 | 6 |
10 | 6 |
8 | 6 |
0 | 6 |
11 | 6 |
11.1.17
17.667
18.
90 | 100 |
100 | 110 |
100 | 90 |
100 | 80 |
110 | 120 |
For Exercises 19–22, do the following:
19. level of significance
11.1.19
(a) , , ; conditions are met. (b) . Reject if . (c) 4.167 (d) Since is not , we do not reject . There is insufficient evidence that the random variable does not follow the distribution specified in .
20. level of significance
21. level of significance
11.1.21
(a) , , , , ; conditions are met. (b) . Reject if . (c) 6.607 (d) Since is not , we do not reject . There is insufficient evidence that the random variable does not follow the distribution specified in .
22. level of significance
For Exercises 23–26, do the following:
23. level of significance
11.1.23
(a) Reject if the -value . , ; conditions are met. (b) 4 (c) -value . (d) Since the -value , we reject . There is evidence that the random variable does not follow the distribution specified in .
24. level of significance
25. level of significance
11.1.25
(a) Reject if the -value . , , , ; conditions are met. (b) 6.083 (c) -value . (d) Since the -value is not , we do not reject . There is insufficient evidence that the random variable does not follow the distribution specified in .
26. level of significance
APPLYING THE CONCEPTS
27. Sales of Children's Books The market share for sales of children's books in 2013 was as follows (Source: PublishersWeekly.com).
Barnes and Noble | Amazon | Others |
---|---|---|
23% | 20% | 57% |
Suppose a survey of 1000 children's book sales this year showed 200 sold by Barnes and Noble, 220 sold by Amazon, and 580 sold by all others. Test whether the population proportions have changed, using level of significance .
11.1.27
: The random variable does not follow the distribution specified in .
Checking the conditions, the expected frequencies are
Because none of these expected frequencies is less than one, and none of the expected frequencies is less than five, the conditions for performing the goodness of ft test are met.
. Reject if .
.
Compare with is . Therefore, we reject . There is evidence that the variable seller does not follow the distribution specified in . In other words, there is evidence that the market share for sales of children's books has changed.
645
28. Believing in Angels. Do you believe in angels? A Gallup Poll found that 78% of respondents believed in angels, 12% were not sure or had no opinion, and 10% didn't believe in angels. Suppose that a survey taken this year of 1000 randomly selected people had the following results.
Believe in angels? | Yes | No | Not sure or no opinion |
---|---|---|---|
Frequency | 820 | 110 | 70 |
Test whether the population proportions have changed, using level of significance .
29. operating System Market Share. NetMarketShare.com reported that, in 2014, the market share for the desktop operating system market was as follows.
Windows 7 | Windows XP | Windows 8 | Others |
---|---|---|---|
51% | 25% | 13% | 11% |
A survey this year of 10,000 randomly selected desktop operating system had the following results.
Windows 7 | Windows XP | Windows 8 | Others |
---|---|---|---|
4500 | 1500 | 2000 | 2000 |
Test whether the population proportions have changed since 2014, using level of significance .
11.1.29
, , , .
: The random variable does not follow the distribution specified in . Checking the conditions, the expected frequencies are , , , , Because none of these expected frequencies is less than one, and none of the expected frequencies is less than five, the conditions for performing the goodness of ft test are met. . Reject if . . Compare with is . Therefore, we reject . There is evidence that the variable operating system does not follow the distribution specified in . In other words, there is evidence that the desktop operating systems market share has changed.
30. Adult Education. The National Center for Education Statistics reported on the percentages of adults who enrolled in personal-interest courses, by the highest education level completed.3 Of these, 8% had less than a high school diploma, 23% had a high school diploma, 32% had some college, 24% had a Bachelor's degree, and 13% had a graduate or professional degree. A survey taken of 200 randomly selected adults who enrolled in personal-interest courses showed the following numbers for the highest education level completed. Test whether the distribution of education levels has changed, using level of significance .
Less than high school |
High school diploma |
Some college |
Bachelor's degree |
Graduate or professional degree |
---|---|---|---|---|
12 | 40 | 62 | 54 | 32 |
31. Mall Restaurants. Based on monthly sales data, the International Council of Shopping Centers reported that the proportions of meals eaten at food establishments in shopping malls were as follows: fast food, 30%; food court, 46%; and restaurants, 24%. A survey of 100 randomly selected meals eaten at malls showed that 32 were eaten at fast-food places, 49 were eaten at food courts, and the rest were eaten at restaurants. Test whether the population proportions have changed, using level of significance
11.1.31
, , . : The random variable does not follow the distribution specified in ,, . Since none of the expected frequencies is less than 1 and none of the expected frequencies is less than 5, the conditions for performing the goodness of ft test are met. . Reject if . . Since is not , we do not reject . There is insufficient evidence that the random variable does not follow the distribution specified in .
32. Spinal Cord Injuries. A study found that, of the minority patients who suffered spinal cord injury, 30% had a private health insurance provider, 55.6% used Medicare or Medicaid, and 14.4% had other arrangements.4 Suppose that a sample of 1000 randomly selected minority patients with spinal cord injuries found that 350 had a private health insurance provider, 500 used Medicare or Medicaid, and 150 had other arrangements. Test whether the proportions have changed, using level of significance .
33. University Dining. The university dining service believes there is no difference in student preference among the following four entrees: pizza, cheeseburgers, quiche, and sushi. A sample of 500 students showed that 250 preferred pizza, 215 preferred cheeseburgers, 30 preferred quiche, and 5 preferred sushi. Test, at level of significance , whether or not there is a difference in student preference among the four entrees. (Hint: For the test of no difference among the proportions, the null hypothesis states that all proportions are equal.)
11.1.33
, , , . : The random variable does not follow the distribution specified in . , , , . Since none of the expected frequencies is less than 1 and none of the expected frequencies is less than 5, the conditions for performing the goodness of ft test are met. . Reject if . . Since , we reject . There is evidence that there is a difference in student preference among the four entries.
34. ISP Market Share. NetMarketShare.com reported that, in 2014, the worldwide market share for the ISP (Internet service provider) market was as follows.
Comcast | AT&T | Time- Warner |
Verizon | Others |
---|---|---|---|---|
7% | 7% | 5% | 5% | 76% |
A survey this year of 10,000 randomly selected ISPs provided the following results.
Comcast | AT&T | Time- Warner |
Verizon | Others |
---|---|---|---|---|
900 | 800 | 600 | 700 | 7000 |
Test whether the population proportions have changed since 2014, using level of significance .
35. Refer to the previous exercise. What if the observed frequency for Comcast had been larger and the observed frequency for Others had been smaller, by some unknown amount? Describe how this would affect the following:
11.1.35
(a) Stay the same (b) Stay the same (c) Increases (d) Decreases (e) Stays the same