## Directions for Comparing Variability

In your study of statistics, you have calculated the mean and the standard deviation of many different samples of data. You have learned that the more the data entries are “spread out”, the greater is the standard deviation.

As a comparative measure of variation, however, the standard deviation has the disadvantage of being dependent upon units of measure. This makes the comparison of measurements from different populations very difficult. The Coefficient of Variation (or CV) defines the standard deviation as a percent of the mean. Since the CV has no units, direct comparison of the variability of different populations may be made.

You will be accessing the United States Department of Labor Bureau of Labor Statistics website http://data.bls.gov and collecting data from the Consumer Price Index (or CPI). Your work will be done on the accompanying worksheet.

Getting Started (Fill in the worksheet as you go.)

1. Access the website and scroll down to CPI - Average Price Data under the heading Prices & Living Conditions. Click onto Most Requested Statistics. From the list, select any two (2) items of interest to you. Retrieve the data.

From the charts, select the most recent year for which all twelve (12) months of prices are complete. It will be more convenient if you print out the data.

2. Access Excel. Find both the mean (AVERAGE) and the standard deviation (STDEV) for each set of data that you have chosen. Print out this work.

3. For each item, calculate the Coefficient of Variation using the formula

CV = (stddev / mean)*100%