Confidence Interval Activity

**Purpose:** To better understand what a confidence interval is.

1. Using the data from the survey, determine the proportion of students at USMA who indicated that they might like to attend a single sex school. This is a small sample of the students at USMA. What can you say about the beliefs of the entire student body at USMA? Calculate a 95% confidence interval for this data. Explain your results.

2. Run the following applet.

You need to enter a value for Q , theta, (population proportion), n (sample size), the number of intervals and the confidence level. Then, you click the recalculate button.

- Explain what a confidence interval is using the green and red lines as part of your explanation.
- Choose a variable from the survey that interests you. For each of the schools, calculate a 95% Confidence Interval for that variable.
- Plot the confidence intervals on the same horizontal axis. What conclusions can you draw?

**Purpose:** To better understand when to use a z-test or a t-test.

1. Review z-tests and t-tests