9.1 Testing Differences in Two Means Day II (Large Samples)

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Presentation transcript:

9.1 Testing Differences in Two Means Day II (Large Samples) By the end of class you will be able to construct confidence intervals for the difference between two means.

Last Lesson: A researcher wants to see if there is a difference in cholesterol levels of two groups of men. A random sample of 30 men between the ages of 25 and 40 had an average cholesterol of 223. A second sample of 25 men between the ages of 41 and 56 had an average of 229. The population standard deviation for both groups is 6. At the .01 level of significance is there a cholesterol difference between the two groups? NOW: Construct the corresponding confidence interval for the difference between the two groups.

Confidence Intervals: Two Samples If the number 0 is in the confidence interval, there is no difference between the groups (____________________) If the number 0 is NOT in the confidence interval, there is a difference between the two groups (_________________) The confidence interval predicts the difference

Last Lesson: Do boys do less housework than girls Last Lesson: Do boys do less housework than girls? In a study of 30 boys and 30 girls, boys were found to do 4.4 hours of chores a week while girls were found to do 5.7 hours of chores a week. Both populations have a standard deviation of .9. Test the claim that boys do less work at a significance level of .05. Now: Construct the corresponding confidence interval for the difference between girls and boys.

Last Lesson: Do employees perform better at work with music playing Last Lesson: Do employees perform better at work with music playing? The music was turned on during the working hours of a business with 45 employees. There productivity level averaged 5.2 with a standard deviation of 2.4. On a different day the music was turned off and there were 40 workers. The workers' productivity level averaged 4.8 with a standard deviation of 1.2. What can we conclude at the .05 level? Now: Construct the corresponding confidence interval for the difference between the groups.

Is there a difference in the number of male and female sports offered at high schools at the .05 level?

The Most Important Thing The most important thing to remember about confidence intervals for two samples is…….. It is also important to remember….. But, the most important thing to remember about confidence intervals for two samples is….