1. SIMS 213: User Interface Design & Development Marti Hearst Thurs, March 13, 2003

2. Experiment Design Example: Marking Menus Pie marking menus can reveal –the available options –the relationship between mark and command 1. User presses down with stylus 2. Menu appears 3. User marks the choice, an ink trail follows

3. What do we want to know? Are marking menus better than pie menus? –Do users have to see the menu? –Does leaving an “ink trail” make a difference? –Do people improve on these new menus as they practice? Related questions: –What, if any, are the effects of different input devices? –What, if any, are the effects of different size menus?

4. Experiment Factors Isolate the following factors (independent variables): –Menu condition exposed, hidden, hidden w/marks (E,H,M) –Input device mouse, stylus, track ball (M,S,T) –Number of items in menu 4,5,7,8,11,12 (note: both odd and even) Response variables (dependent variables): –Response Time –Number of Errors

5. Experiment Hypotheses Note these are stated in terms of the factors (independent variables) –Exposed menus will yield faster response times and lower error rates, but not when menu size is small –Response variables will monotonically increase with menu size for exposed menus –Response time will be sensitive to number of menu choices for hidden menus (familiar ones will be easier, e.g., 8 and 12) –Stylus better than Mouse better than Track ball

6. Experiment Hypotheses Device performance is independent of menu type Performance on hidden menus (both marking and hidden) will improve steadily across trials. Performance on exposed menus will remain constant.

7. Experiment Design One between-subjects factor –Menu Type Three levels: E, H, or M Two within-subjects factors –Device Type Three levels: M, T, or S –Number of Menu Items Six levels: 4, 5, 7, 8, 11, 12 How should we arrange these?

8. Experiment Design M T S T S M S M T EHM 511 128 74 Block by size then randomize the blocks. (Note: the order of each set of blocks will differ for each participant in each square)

9. Experiment Overall Results So exposing menus is faster … or is it? Let’s factor things out more.

10. A Learning Effect When we graph over the number of trials, we find a difference between exposed and hidden menus. This suggests that participants may eventually become faster using marking menus (was hypothesized). A later study verified this.

11. Factoring to Expose Interactions Increasing menu size increases selection time and number of errors (was hypothesized). No differences across menu groups in terms of response time. That is, until we factor by menu size AND group –Then we see that menu size has effects on hidden groups not seen on exposed group –This was hypothesized (12 easier than 11)

12. Factoring to Expose Interactions Stylus and mouse outperformed trackball (hypothesized) Stylus and mouse the same (not hypothesized) Initially, effect of input device did not interact with menu type –this is when comparing globally –BUT... More detailed analysis: –Compare both by menu type and device type –Stylus significantly faster with Marking group –Trackball significantly slower with Exposed group –Not hypothesized!

13. Average response time and errors as a function of device, menu size, and menu type. Potential explanations: Markings provide feedback for when stylus is pressed properly. Ink trail is consistent with the metaphor of using a pen.

14. Experiment Design M T S T S M S M T EHM How can we tell if order in which the device appears has an effect on the final outcome? Some evidence: There is no significant difference among devices in the Hidden group. Trackball was slowest and most error prone in all three cases. Still, there may be some hidden interactions, but unlikely to be strong given the previous graph.

15. Statistical Tests Need to test for statistical significance –This is a big area –Assuming a normal distribution: Students t-test to compare two variables ANOVA to compare more than two variables

16. Adapted from slide by James Landay Analyzing the Numbers Example: trying to get task time <=30 min. –test gives: 20, 15, 40, 90, 10, 5 –mean (average) = 30 –median (middle) = 17.5 –looks good! –wrong answer, not certain of anything Factors contributing to our uncertainty –small number of test users (n = 6) –results are very variable (standard deviation = 32) std. dev. measures dispersal from the mean

17. Adapted from slide by James Landay Analyzing the Numbers (cont.) This is what statistics is for Crank through the procedures and you find –95% certain that typical value is between 5 & 55 Usability test data is quite variable –need lots to get good estimates of typical values –4 times as many tests will only narrow range by 2x

18. Followup Work Hierarchical Markup Menu study

19. Followup Work Results of use of marking menus over an extended period of time –two person extended study –participants became much faster using gestures without viewing the menus

20. Followup Work Results of use of marking menus over an extended period of time –participants temporarily returned to “novice” mode when they had been away from the system for a while

21. Summary Formal studies can reveal detailed information but take extensive time/effort Human participants entail special requirements Experiment design involves –Factors, levels, participants, tasks, hypotheses –Important to consider which factors are likely to have real effects on the results, and isolate these Analysis –Often need to involve a statistician to do it right –Need to determine statistical significance –Important to make plots and explore the data

22. References Kurtenbach, Sellen, and Buxton, Some Articulartory and Cognitive Aspects of “Marking Menus”, Graphics Interface ‘94, http://reality.sgi.com/gordo_tor/papers Kurtenbach and Buxton, User Learning and Performance with Marking Menus, Graphics Interface ‘94, http://reality.sgi.com/gordo_tor/papers Jain, The art of computer systems performance analysis, Wiley, 1991 http://www.statsoft.com/textbook/stanman.html Gonick and Smith, The Cartoon Guide to Statistics, HarperPerennial, 1993 Dix et al. textbook