Assignment: Create a Confidence Interval
1. A hardware store want to use a sample to find the proportion of their customers are men. A
statistician starts with the null hypothesis that exactly half are men. Create a normal
sampling distribution using StatKey:
http://lock5stat.com/statkey/bootstrap_1_cat/bootstrap_1_cat.html
The store keeps track of the proportion of male customers that enter the store for one week.
The proportion of this sample is .66. Use the bootstrap normal sampling distribution from
StatKey and create a 95% confidence interval about the sample proportion of .66.
Write a short paragraph about what the confidence interval means.
Does the confidence interval contain .5 (the null hypothesis)? What does this mean?
2. A school district wants to know the proportion of students who can correctly name all the
capitals of all fifty states after taking a geography course. They have a standard of wanting
¾ or .75 of those who successfully complete the course to be able to name them all. They
use this as a null hypothesis. Create a normal sampling distribution using StatKey:
http://lock5stat.com/statkey/bootstrap_1_cat/bootstrap_1_cat.html
The district tests a few classes and finds the actual proportion is .6. Use the bootstrap normal
sampling distribution from StatKey and create a 95% confidence interval about the sample
proportion of .6.
Write a short paragraph about what the confidence interval means.
Does the confidence interval contain .75 (the goal proportion)? What does this mean?
Answer Key to:
Assignment – Create a confidence interval Answers in Red
1. A hardware store want to use a sample to find the proportion of their customers are men. A
statistician starts with the null hypothesis that exactly half are men. Create a normal
sampling distribution using StatKey:
http://lock5stat.com/statkey/bootstrap_1_cat/bootstrap_1_cat.html
The store keeps track on the proportion of male customers that enter the store for one week.
The proportion of this sample is .66. Use the bootstrap normal sampling distribution from
StatKey and create a 95% confidence interval about the sample proportion of .66.
Using 5000 simulated samples, the confidence interval is about .66  .08 or .58 to .72
Write a sentence or two about what the confidence interval means.
We are 95% certain that the true proportion of males of all customers who enter the store is
between .58 and .72.
Does the confidence interval contain .5 (the null hypothesis)? What does this mean?
The confidence interval does not contain .5, so we are 95% certain that it is not true that half
the customers entering the store are men.
2. A school district wants to know the proportion of students who can correctly name all the
capitals of all fifty states after taking a geography course. They have a standard of wanting
¾ or .75 of those who successfully complete the course to be able to name them all. They
use this as a null hypothesis. Create a normal sampling distribution using StatKey:
http://lock5stat.com/statkey/bootstrap_1_cat/bootstrap_1_cat.html
The district tests a few classes and finds the actual proportion is .71. Use the bootstrap
normal sampling distribution from StatKey and create a 95% confidence interval about the
sample proportion of .6.
Using 5000 simulated samples, the confidence interval is about .71  .042 or .668 to .752
Write a sentence or two about what the confidence interval means.
We are 95% certain that the true proportion of those who can correctly name all the state
capitals after completing the geography course is between .668 and .752.
Does the confidence interval contain .75 (the goal proportion)? What does this mean?
The confidence interval does contain .75, so it is possible that the true proportion is .7
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Confidence Intervals Assignment