# Confidence Intervals for the Mean

## Difference between Means

### Questions

Question 1 out of 4.
Select all of the assumptions that you need to make when creating a confidence interval on the difference between means.

At least 2% of the population sampled

Independently sampled values

Homogeneity of variance

Normally distributed populations

Question 2 out of 4.
You are comparing men and women on hours spent watching TV. You pick a sample of 12 men and 14 women and calculate a confidence interval on the difference between means. How many degrees of freedom does your t value have?

Question 3 out of 4.
You are comparing freshmen and seniors at your college on hours spent studying per day. You pick a sample of 11 people from each group. For freshmen, the mean was 3 and the variance was 1.2. For seniors, the mean was 2 and the variance was 1. Calculate a 90% confidence interval on the difference between means (freshmen - seniors). What is the lower limit of this CI?

Question 4 out of 4.
Scores on a test taken by 1st graders and 2nd graders were compared to look at development. The five 1st graders sampled got the following scores: 4, 3, 5, 7, 4. The five 2nd graders sampled got the following scores: 7, 9, 8, 6, 9. Compute the 95% confidence interval for the difference between means (2nd graders - 1st graders). You may use the Analysis Lab. What is the upper limit?

Grade	Score
1	  4
1	  3
1	  5
1	  7
1	  4
2	  7
2	  9
2	  8
2	  6
2	  9