You don't need Minitab or Statdisk for this question. Go to the statistical demonstrations page and choose the Confidence Interval Simulation from section 6.2.

Read the Harris Poll® #71, September 15, 2005, at http://www.harrisinteractive.com/harris_poll/index.asp?PID=601

- Choose Analysis / Confidence Intervals / Proportion One Sample
- Enter your confidence level as a decimal
- Enter the sample size, n, for the survey that you found for part b.
- Enter the number of successes, x, which represents the number of people who feel that Bush has done a poor job of handling the Katrina Relief. This is NOT the percent of people that you found for part a, but you'll have to take that percent of the total sample size and round it to a whole number to enter here.
- Click Evaluate

The following example assumes that you were assigned "September". You should replace that with whatever month you were given to work with.

- Visit the National Weather Service's archive page at http://www.crh.noaa.gov/ilx/archive.php.
- Choose the Decatur Arpt box and select the month September 2005
- Record the "AVG SPD" for the Wind from column 10 for each of the days in September 2005. While you're at it, you might as well go ahead and collect the "AVG" for the temperature from column 4 because you'll need it for question 4.
- Click the Back button and choose September 2004
- Record the "AVG SPD" for the Wind from column 10 for each of the days in September 2004.
- Click the Back button and choose September 2003
- Record the "AVG SPD" for the Wind from column 10 for each of the days in September 2003.

- Click on the 1 at the top of the first column and label the first column as
**wind** - If you happened to gather the temperature data, then label the second column as
**temp** - Enter the data into the appropriate columns

You can't find the confidence interval directly from the data like you could with Minitab. You need to do descriptive statistics first, write those numbers down, and then go do the confidence interval.

- Choose Data / Descriptive Statistics
- Select column 1 (the wind data)
- Click Evaluate
- Write down the sample size, mean, and st dev. Don't round the values.
- If you gathered the temperature data as suggested, then go ahead and repeat this with column 2 (the temperature data)

- Choose Analysis / Confidence Intervals / Mean-One Sample
- Enter the confidence level as a decimal
- Enter the sample size, sample mean, and sample st dev that you found from the descriptive statistics screen
- Leave the population st dev blank
- Click Evaluate

When Statdisk gives the confidence interval, it will look something like 5.62333 < mean < 7.31215. You should write it as 5.62333 mph < μ < 7.31215 mph.

If you already collected the temperature data for question 3, then you can skip straight to the Confidence Interval section.

The following example assumes that you were assigned "September". You should replace that with whatever month you were given to work with.

- Visit the National Weather Service's archive page at http://www.crh.noaa.gov/ilx/archive.php.
- Choose the Decatur Arpt box and select the month September 2005
- Record the "AVG" for the temperature from column 4.

- Label an empty column as
**temp** - Enter the data into the
**temp**column.

You can't find the confidence interval directly from the data like you could with Minitab. You need to do descriptive statistics first, write those numbers down, and then go do the confidence interval.

- Choose Data / Descriptive Statistics
- Select the column where you stored the temperature data.
- Click Evaluate
- Write down the sample size, mean, and st dev. Don't round the values.

- Choose Analysis / Confidence Intervals / Mean-One Sample
- Enter the confidence level as a decimal
- Enter the sample size, sample mean, and sample st dev that you found from the descriptive statistics screen
- Leave the population st dev blank
- Click Evaluate

When Statdisk gives the confidence interval, it will look something like 74.3824 < mean < 77.6821. You should write it as 74.3824 °F < μ < 77.6821 °F.

Visit the Weatherbase at http://www.weatherbase.com/. Do a search for "Decatur, IL" and find the average temperature for your month.