IT 223: Data Analysis
Winter 2006

Assignment 3

Due Friday January 27 before 11:30pm by DL Web Submission

Overview

For this assignment, you will be studying the relationship between the position of a hyptertext link in a list and the time needed to click on that link.

Plotting the data

Several years ago, I conducted a Web navigation study where I asked participants to find various retail goods in a Web site. They searched for items like coffee grinders, electric mixers and chopsticks. One item was a birdbath. When they reached the page with this item, they had to scan a list of 11 links. The link labeled "Birdbath" was randomly positioned among the 11 links. I recorded its link position (numbered 1 through 11) and the time it took for them to select this link. The file for this data is menu.xls. Each row represents one navigation result. The first column is the position in the list where the desired link ("Birdbath") was located. The second column is the time in milliseconds needed to scan the links and click on the desired link. Assuming that people scan lists from top to bottom, a low target position should have a faster click time.

Using Excel plot the data set. Have the link position be the independent variable (x-axis) and the time be the dependent variable (y-axis). To make your calculations easier, use Excel to report the average and standard deviation for both variables.

You do not need to turn in your entire Excel spreadsheet.

Calculations and analysis

  1. Report the average (mean) and standard deviation (sample version) of both variables.
  2. Report standard scores for both variables, their products and the correlation coefficient. Note that this is the general process for calculating the correlation coefficient.
  3. Use Excel to draw the regression line and report the equation of the regression line. Paste the scatterplot in your report.
  4. What is the slope of the regression line?
  5. What is the y-intercept of the regression line?
  6. Name the one point that is intersected by both the standard deviation line and the regression line.
  7. What is the slope of the standard deviation line?
  8. Using the equation for the regression line, how much time it would take a user to scan the menu and click on the fourth item?
  9. Using your equation for the regression line, how much time does an average user require to scan each link? That is, how much time does it take to consider one link before moving on to consider the next link (Hint: think about the task and what would be reasonable)
  10. Using your equation for the regression line, how much time does it take an average user to click on a link (after the user has scanned and found the needed link)?
  11. To what extent did these participants scan the list from top to bottom? Discuss (approximately 1 paragraph).

Submission

Turn in a softcopy (contained in one document) of your answers and graph using the dlweb site.