1. Chapter 9 Review

2. Step 1: Decide Proportion or Mean
Create Null and alternative hypotheses
H0:
Ha:
Find P-hat
Number of “successes” divided by sample size
Create null and alternative hypotheses
Find X-bar
Find Sx
Find Degrees of freedom
Option 1: “By hand”
Find t
Tcdf to find p-value
Reject or fail to reject null
Option 2: Calculator
T-test
Report t and p-value
Reject or fail to reject null
Option 1: “by hand”
Find Z
Normalcdf to find p-value
Reject or fail to reject null
Option 2: Calculator
1-propZtest
Report Z and p-value
Reject or fail to reject null

3. Remember:
Significance tests are only useful when we don’t know what the true value is in the population
If we already know the population mean/proportion, then we can just say “yes, the null is correct” or “no, the null is wrong—here is what the true value is”
Significance tests only useful when we have sample data and want to draw conclusions about the entire population

4. Example
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When Mr. Wetherbee plays golf, he claims that he drives the ball 250 yards, on average. You don’t believe him, and think that his average drive is different from 250 yards. A sample of 10 of his drives is shown to the right. Is there enough evidence to conclude that he is wrong?

5. Example
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When Mr. Wetherbee plays golf, he claims that he drives the ball 250 yards, on average. You don’t believe him, and think that his average drive is different from 250 yards. A sample of 10 of his drives is shown to the right. Is there enough evidence to conclude that he is wrong?
YES. P-value=.026. Reject Null

6. Example 1
A company claims that 60% of graduate students have bought school supplies online. A consumer group believes that this estimate is too low. A random sample of 80 graduate students shows that 55 of them have bought supplies online. Is there enough evidence, at a .05 significance level, to conclude that the company’s claim is wrong?

7. Example 1
A company claims that 60% of graduate students have bought school supplies online. A consumer group believes that this estimate is too low. A random sample of 80 graduate students shows that 55 of them have bought supplies online. Is there enough evidence, at a .05 significance level, to conclude that the company’s claim is wrong?
NO. P-value=.055. Fail to reject the null

8. Example 3
A high school claims that, on average, each class has 3 people missing per day. Based on your experience, you think that more than 3 people are absent each day. You randomly sample 10 classes over the course of a week. In your sample, you find a mean number of absent students to be 4.1 with a standard deviation of 1.1
At which of the following significance levels would we be able to conclude that the school is wrong (choose all that apply): .1
.05
.01
.005
.001