To Activities

LSP 121 -- Activity 3

The Standard Deviation and z-scores

 

  1. Use calculate the mean and SD+ of the following list by hand:

    Then compute the z-scores by hand. Use SPSS to check your answer.

  2. Open the Excel file Downtime.xls on the QRC website qrc.depaul.edu. The file relates to a manufacturer of computer systems which is interested in improving its customer support services. As a first step, its marketing department has been charged with the responsibility of summarizing the extent of customer problems in terms of system downtime. The most recent 40 customers were surveyed to determine the amount of downtime (in hours) they had experienced during the previous month. The file contains the customer client number and their down time hours.

    Using SPSS, calculate average, max, min, and standard deviation. Create a new column for the z-scores. Were there any customers who had an exceedingly high number of hours of downtime the previous month (z-score greater than 2.0)? In a short paragraph, tell what you would do as a result of this analysis if you were a member of the customer support department and were trying to improve customer relations?

  3. Find the outliers for hours using the boxplot. Are they different than the customers that have z-scores larger than 2.0?