chapter 9 testing the difference between two means, two proportions, and two variances mcgraw-hill,...
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Chapter 9
Testing the Difference Between Two Means, Two Proportions, and Two Variances
McGraw-Hill, Bluman, 7th ed., Chapter 9 1
Bluman, Chapter 9 2
Test 9Thursday March 21
This the last day the class meets before spring break starts.Please make sure to be present for the test or make appropriate arrangements to take the test before leaving for spring break
Chapter 9 Overview Introduction 9-1 Testing the Difference Between Two
Means: Using the z Test
9-2 Testing the Difference Between Two Means of Independent Samples: Using the t Test
9-3 Testing the Difference Between Two Means: Dependent Samples
9-4 Testing the Difference Between Proportions
9-5 Testing the Difference Between Two Variances
Bluman, Chapter 9 3
Chapter 9 Objectives1. Test the difference between sample means,
using the z test.
2. Test the difference between two means for independent samples, using the t test.
3. Test the difference between two means for dependent samples.
4. Test the difference between two proportions.
5. Test the difference between two variances or standard deviations.
Bluman, Chapter 9 4
Section 9-1 Introduction
Pepsi vs. Coke
9.1 Testing the Difference Between Two Means: Using the z Test
Assumptions:1. The samples must be independent of each
other. That is, there can be no relationship between the subjects in each sample.
2. The standard deviations of both populations must be known, and if the sample sizes are less than 30, the populations must be normally or approximately normally distributed.
Bluman, Chapter 9 6
Hypothesis Testing Situations in the Comparison of Means
Bluman, Chapter 9 7
Hypothesis Testing Situations in the Comparison of Means
Bluman, Chapter 9 8
Testing the Difference Between Two Means: Large Samples
Formula for the z test for comparing two means from independent populations
Bluman, Chapter 9 9
1 2 1 2
2 21 2
1 2
X Xz
n n
Chapter 9Testing the Difference Between Two Means, Two Proportions, and Two Variances
Section 9-1Example 9-1
Page #475
Bluman, Chapter 9 10
Example 9-1: Hotel Room CostA survey found that the average hotel room rate in New Orleans is $88.42 and the average room rate in Phoenix is $80.61. Assume that the data were obtained from two samples of 50 hotels each and that the standard deviations of the populations are $5.62 and $4.83, respectively. At α = 0.05, can it be concluded that there is a significant difference in the rates?
Step 1: State the hypotheses and identify the claim.
H0: μ1 = μ2 and H1: μ1 μ2 (claim)
Step 2: Find the critical value.
The critical value is z = ±1.96.
Bluman, Chapter 9 11
Example 9-1: Hotel Room CostA survey found that the average hotel room rate in New Orleans is $88.42 and the average room rate in Phoenix is $80.61. Assume that the data were obtained from two samples of 50 hotels each and that the standard deviations of the populations are $5.62 and $4.83, respectively. At α = 0.05, can it be concluded that there is a significant difference in the rates?
Step 3: Compute the test value.
Bluman, Chapter 9 12
1 2 1 2
2 21 2
1 2
X Xz
n n
Example 9-1: Hotel Room CostA survey found that the average hotel room rate in New Orleans is $88.42 and the average room rate in Phoenix is $80.61. Assume that the data were obtained from two samples of 50 hotels each and that the standard deviations of the populations are $5.62 and $4.83, respectively. At α = 0.05, can it be concluded that there is a significant difference in the rates?
Step 3: Compute the test value.
Bluman, Chapter 9 13
2 2
88.42 80.61 0
5.62 4.8350 50
z 7.45
Step 4: Make the decision.
Reject the null hypothesis at α = 0.05, since 7.45 > 1.96.
Step 5: Summarize the results.
There is enough evidence to support the claim that the means are not equal. Hence, there is a significant difference in the rates.
Example 9-1: Hotel Room Cost
Bluman, Chapter 9 14
Chapter 9Testing the Difference Between Two Means, Two Proportions, and Two Variances
Section 9-1Example 9-2
Page #475
Bluman, Chapter 9 15
Example 9-2: College Sports OfferingsA researcher hypothesizes that the average number of sports that colleges offer for males is greater than the average number of sports that colleges offer for females. A sample of the number of sports offered by colleges is shown. At α = 0.10, is there enough evidence to support the claim? Assume 1 and 2 = 3.3.
Bluman, Chapter 9 16
Example 9-2: College Sports OfferingsStep 1: State the hypotheses and identify the claim.
H0: μ1 = μ2 and H1: μ1 μ2 (claim)
Step 2: Compute the test value.
Using a calculator, we find
For the males: = 8.6 and 1 = 3.3
For the females: = 7.9 and 2 = 3.3
Substitute in the formula.
Bluman, Chapter 9 17
1 2 1 2
2 21 2
1 2
X Xz
n n
1X
2X
2 2
8.6 7.9 01.06
3.3 3.350 50
Example 9-2: College Sports Offerings
Bluman, Chapter 9 18
Step 3: Find the P-value. For z = 1.06, the area is 0.8554.The P-value is 1.0000 - 0.8554 = 0.1446.
Step 4: Make the decision. Do not reject the null hypothesis.
Step 5: Summarize the results. There is not enough evidence to support the claim that colleges offer more sports for males than they do for females.
Confidence Intervals for the Difference Between Two Means
Formula for the z confidence interval for the difference between two means from independent populations
Bluman, Chapter 9 19
2 21 2
1 2 2 1 21 2
2 21 2
1 2 21 2
X X zn n
X X zn n
Chapter 9Testing the Difference Between Two Means, Two Proportions, and Two Variances
Section 9-1Example 9-3
Page #478
Bluman, Chapter 9 20
Example 9-3: Confidence IntervalsFind the 95% confidence interval for the difference between the means for the data in Example 9–1.
Bluman, Chapter 9 21
2 21 2
1 2 2 1 21 2
2 21 2
1 2 21 2
X X zn n
X X zn n
2 2
1 2
2 2
5.62 4.8388.42 80.61 1.96
50 505.62 4.83
88.42 80.61 1.9650 50
1 27.81 2.05 7.81 2.05
1 25.76 9.86
On your own
Study the examples in section 9.1
Sec 9.1 page 479 #7,13,16 19, 21
Bluman, Chapter 9 22