i213: User Interface Design & Development Marti Hearst March 1, 2007

Today Wireframing Being Formal Usability Studies

Wireframing What is the main idea? –A visual guide to suggest the layout and placement of fundamental design elements –Separate content from layout and display –Allow for development of variatinos of the layout to support consistency –Use elements from graphic design Use the page layout to signal the flow of interaction Group conceptually related items together

Example (By Lisa Hankin)

Wireframing Nielsen: –usability of the layout specified by the template design –usability of the specific content that has been poured into this template on the individual pages Questions to ask: –What does the layout communicate? –Does a page of content becomes more usable because of the layout? –A template (for a home page) should contain what items?

From

Wireframing Study How to test a layout Study conducted by Thomas S. Tullis from Fidelity Investments in 1998 Assessed the usability of five alternative template designs for their intranets. Method: –Show templates with “greeked” text –Draw labeled boxes around each page corresponding to 9 elements –No overlapping allowed –Indicate if something appears not to be there

The Elements 1.Main content selections for this page 2.Page title 3.Person responsible for this page 4.Intranet-wide navigation (e.g., intranet home, search) 5.Last updated date 6.Intranet identifier/logo 7.Site navigation (e.g, major sections of this section of the intranet) 8.Confidentiality/security (e.g, Public, Confidential, etc.) 9.Site news items

From

Wireframing Study Different parts of the designs scored better Best parts were taken from each design and combined Resulted in an overall better score

Results of Study Correct Page Elements Subjective Appeal (-3 to +3) Template 152%+1.3 Template 367%+0.9 Final Design72%+2.1

Formal Usability Studies

Outline Experiment Design –Factoring Variables –Interactions Special considerations when involving human participants

Adapted from slide by James Landay Formal Usability Studies When useful –to determine time requirements for task completion –to compare two designs on measurable aspects time required number of errors effectiveness for achieving very specific tasks Requires Experiment Design

Experiment Design Experiment design involves determining how many experiments to run and which attributes to vary in each experiment Goal: isolate which aspects of the interface really make a difference

Experiment Design Decide on –Response variables the outcome of the experiment usually the system performance aka dependent variable(s) –Factors (aka attributes) aka independent variables –Levels (aka values for attributes) –Replication how often to repeat each combination of choices

Experiment Design Example: –Studying a system (ignoring users) Say we want to determine how to configure the hardware for a personal workstation –Hardware choices which CPU (three types) how much memory (four amounts) how many disk drives (from 1 to 3) –Workload characteristics administration, management, scientific

Experiment Design We want to isolate the effect of each component for the given workload type. How do we do this? –WL1CPU1 Mem1Disk1 –WL1CPU1Mem1Disk2 –WL1CPU1Mem1Disk3 –WL1CPU1Mem2Disk1 –WL1CPU1Mem2Disk2 –…–… There are (3 CPUs)*(4 memory sizes)*(3 disk sizes)*(3 workload types) = 108 combinations!

Experiment Design One strategy to reduce the number of comparisons needed: –pick just one attribute –vary it –hold the rest constant Problems: –inefficient –might miss effects of interactions

Interactions among Attributes A1A2 B135 B268 A1 A2 B135 B2612 A1 B1 A2 A1 B2 A2 B2 A and B do not interactA and B may interact A2 A1 B1B2B1B2

Experiment Design Another strategy: figure out which attributes are important first Do this by just comparing a few major attributes at a time –if an attribute has a strong effect, include it in future studies –otherwise assume it is safe to drop it This strategy also allows you to find interactions between attributes

Experiment Design Common practice: Fractional Factorial Design –Just compare important subsets –Use experiment design to partially vary the combinations of attributes Blocking –Group factors or levels together –Use a Latin Square design to arrange the blocks

Between-Groups Design Wilma and Betty use one interface Dino and Fred use the other

Within-Groups Design Everyone uses both interfaces

Adapted from slide by James Landay Between-Groups vs. Within-Groups Between groups –2 or more groups of test participants –each group uses only 1 of the systems Within groups –one group of test participants –each person uses all systems can’t use the same tasks on different systems

Between Groups Example Comparing TextEdge to Graffiti Wobbrock, J.O., Myers, B.A. and Kembel, J.A. (2003) EdgeWrite: A stylus-based text entry method designed for high accuracy and stability of motion. (UIST '03).

Between Groups Example Comparing TextEdge to Graffiti Wobbrock, J.O., Myers, B.A. and Kembel, J.A. (2003) EdgeWrite: A stylus-based text entry method designed for high accuracy and stability of motion. (UIST '03). –Independent Variables? –Dependent Variables? –Between or Within Subjects?

Between Groups Example Comparing TextEdge to Graffiti –Independent Variables? TextEdge vs Graffiti! –Dependent Variables? Time Errors –Between or Within Subjects? Between, to control for learning effects

Between-Groups vs. Within-Groups Within groups design –Pros: Is more powerful statistically (can compare the same person across different conditions, thus isolating effects of individual differences) Requires fewer participants than between-groups –Cons: Learning effects Fatigue effects

Special Considerations for Formal Studies with Human Participants Studies involving human participants vs. measuring automated systems –people get tired –people get bored –people (may) get upset by some tasks –learning effects people will learn how to do the tasks (or the answers to questions) if repeated people will (usually) learn how to use the system over time

More Special Considerations High variability among people –especially when involved in reading/comprehension tasks –especially when following hyperlinks! (can go all over the place)