CMSC 838G - Fall 2005
Prof Guimbretière

Advanced Introduction to HCI

Homework #1 (due 10/11/04):
Experiment replication: Fitts' law

The goal of this homework is to replicate part of the experiment presented in MacKenzie's CHI'92 paper on Fitts' law.

What to do

Experimental apparatus

Build an experimental apparatus similar to the one described in the paper. Your program should be able to record how fast a user might click (with the mouse) between two targets on the screen in several conditions. For the purpose of this homework the conditions will be:

• 4 possible value of ID using formula (3)

• For each ID two possible combinations of Length and target Wdth

• Targets will be square

• Targets will stay on the horizontal axis

For each conditions, the participant will repeat the task ten times before the program displays a new condition.

You are asked to use the apparatus you built to measure the performance of at 4 participants (none of them should be a student in this class).  Exceptionally for this homework, you will not be required to provide a consent form, but you will be asked that for each participant, you debrief them about the purpose of the experiment after it was conducted. Note that once the experiment has started, you cannot change the apparatus. Be sure to debug your system thoroughly before starting with participants.

Deliverables

Your are asked to provide a 2-3 pages experiment report including:

• (10 points) An introduction describing in you own words the purpose of your experiment

• (20 points) A description of your apparatus including the ID you picked, and for each ID which Length you picked, a screen shot of your program showing one condition, and how you validated the time measurement of your apparatus. Explain all your choices

• (20 points) A description of the protocol you used to run participants. The protocol should include, how you trained your participants, an explanation of how the apparatus cycle through the different conditions, and how the participants were debriefed after the experiment

• (20 points) A description of the results of the experiment including a plot showing for each ID the average time for this ID, the confidence interval for that ID, the linear regression curve and the r^2 value for these averages (all these values can be computed using Excel functions including: average, confidence, and for the regression by adding a trend line to your graph).

• (10 points) A brief report of comments from users if any, and possible problems you observed during the experiment

• (20 points) A discussion of your results including an explanation of possible discrepancy between your findings and the theory.