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Blackmon, Kitajima, & Polson, CHI2005 1/26 Tool for Accurately Predicting Website Navigation Problems, Non-Problems, Problem Severity, and Effectiveness of Repairs Marilyn Hughes Blackmon, U. of Colorado Muneo Kitajima, AIST, Japan Peter Polson, U. of Colorado

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Blackmon, Kitajima, & Polson, CHI2005 2/26 Part One Work supported by NSF Grant 01-37759 to M. H. Blackmon http://autocww.colorado.edu/~brownr/ACWW.php http://autocww.colorado.edu/~blackmon http://autocww.colorado.edu

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Blackmon, Kitajima, & Polson, CHI2005 3/26 Problem that spurred research and development of tool Focus on users building comprehensive knowledge of a topic Browse complex websites (cf. search engine) Pure forward search Learn by exploration Automatically predict what is worth repairing? Need accurate measure of problem severity Need to predict success rate for repairs Web designers using tool must be able to do what unaided designers cannot: predict behavior of users different from themselves – objectively represent user diversity (background knowledge)

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Blackmon, Kitajima, & Polson, CHI2005 4/26 Solution: Incrementally extend Cognitive Walkthrough for the Web (CWW) CHI2002 paper tailored Cognitive Walkthrough (CW) for web navigation Proved CWW would identify usability problems that interfere with web navigation Substituted objective measures of similarity, familiarity, and elaboration of heading/link texts using Latent Semantic Analysis (LSA) CHI2003 paper proved significantly better performance on CWW-repaired webpages vs. original, unrepaired pages

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Blackmon, Kitajima, & Polson, CHI2005 5/26 Percent task failure correlated 0.93 with observed clicks (each task n≥38)

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Blackmon, Kitajima, & Polson, CHI2005 6/26 Research problem, reformulated: What determines mean clicks? Identify & repair factors that increase mean clicks and raise risk of task failure Hypothetical determinants, based on prior results and theory underlying CWW research: Unfamiliar correct link, i.e., insufficient background knowledge to comprehend link Competing headings & their high-scent links Competing links under correct heading Weak scent correct link under correct heading

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Blackmon, Kitajima, & Polson, CHI2005 7/26 First step: Collect enough data for multiple regression analysis Reused 64 tasks from CHI2003 paper and ran additional experiments to get data on 100 new tasks, creating 164- task dataset Developed automatable rules for CWW problem identification Built multiple regression model for 164- task dataset and found 3 independent variables explaining 57% of the variance

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Blackmon, Kitajima, & Polson, CHI2005 8/26 Multiple regression translates into formula to predict problem severity Multiple regression analysis yielded formula for predicting mean clicks on links: + 2.199 (predicted clicks for non-problem) + 1.656 if correct link is unfamiliar + 0.754 times number of competing links nested under any competing heading + 1.464 if correct link has weak-scent + zero clicks for competing links under correct heading Prediction for non-problem task = 2.199 ≥2.5 mean clicks distinguishes problem from non- problem

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Blackmon, Kitajima, & Polson, CHI2005 9/26 Example of task: Find article about Hmong: List of 9 categories > Social Science > Anthropology Scroll A-Z list to find Hmong

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Blackmon, Kitajima, & Polson, CHI2005 10/26

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Blackmon, Kitajima, & Polson, CHI2005 11/26 CWW-identified problems in “Find Hmong” task: Competing headings 0.30 0.08 0.19

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Blackmon, Kitajima, & Polson, CHI2005 12/26 Predicted mean clicks for Find Hmong task on original, unrepaired webpage + 2.199 -- predicted clicks for non-problem + 1.656 -- if correct link is unfamiliar + 1.464 -- if correct link has weak-scent + 3.770 -- (0.754 *5, the number of competing links nested under any competing heading) _________ 9.089 -- predicted mean total clicks

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Blackmon, Kitajima, & Polson, CHI2005 13/26 CWW-guided repairs of navigation usability problems detected by CWW Create alternate high-scent paths to target webpage via all correct and competing headings IF competing heading(s) IF unfamiliar correct link IF weak-scent correct link Substitute or elaborate link text with familiar, higher frequency words IF unfamiliar correct link

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Blackmon, Kitajima, & Polson, CHI2005 14/26 Repair benefits for “Find Hmong,” a problem definitely worth repairing

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Blackmon, Kitajima, & Polson, CHI2005 15/26 All 164 tasks: Predicted vs. observed mean total clicks

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Blackmon, Kitajima, & Polson, CHI2005 16/26 Psychological validity measures for 164-task dataset For 46 tasks predicted to have serious problems (i.e., predicted clicks ≥ 5.0) 100% hit rate, 0% false alarms 93% success rate for repairs (statistically significant difference repaired vs. not) For all 75 tasks predicted to be problems 92% hit rate, 8% false alarms 83% success rate for repairs, significant different repaired vs. unrepaired, p<.0001

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Blackmon, Kitajima, & Polson, CHI2005 17/26 Cross-validation study: Replicate the model on new dataset? Ran another large experiment to test whether multiple regression formula replicated with new set of tasks 2 groups Each group did 32 new tasks, 64 total tasks Used prediction formula to identify problems vs. non-problems All tasks have just one correct link

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Blackmon, Kitajima, & Polson, CHI2005 18/26 Multiple regression analysis produced full cross validation Multiple regression of 64-task dataset gave same 3 determinants found for 164- task original dataset & similar coefficients Hit rate for predicted problems = 90%, false alarms = 10% Correct rejection for predicted non- problems = 69%, 31% misses, but 2/3 of misses had observed clicks 2.5-3.5, other 1/3 of misses >3.5 but <5.0

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Blackmon, Kitajima, & Polson, CHI2005 19/26 Predicted vs. observed clicks for 64 tasks in cross-validation experiment

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Blackmon, Kitajima, & Polson, CHI2005 20/26 Part Two

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Blackmon, Kitajima, & Polson, CHI2005 21/26 Theory matters: CWW is theory-based usability evaluation method CoLiDeS cognitive model (Kitajima, Blackmon, & Polson, 2000, 2005) Construction-Integration cognitive architecture (Kintsch, 1998), a comprehensive model of human cognitive processes Latent Semantic Analysis (LSA)

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Blackmon, Kitajima, & Polson, CHI2005 22/26 The Key Idea Core process underlying Web navigation is skilled reading comprehension Comprehension processes build mental representations of goals and webpage objects (subregions, hyperlinks, images, and other targets for action) Action planning compares goal with potential targets for action and selects target with highest activation level

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Blackmon, Kitajima, & Polson, CHI2005 23/26 Consensus: Web navigation is equivalent to following scent trail Scent or residue (Furnas, 1997) SNIF-ACT based on Information Foraging (Pirolli & Card, 1999) Bloodhound Project: Web User Flow by Information Scent (WUFIS) => InfoScent Simulator (Chi, et al., 2001, 2003) CWW activation level

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Blackmon, Kitajima, & Polson, CHI2005 24/26 CoLiDeS activation level: Scent is MORE than just similarity Adequate background knowledge to comprehend headings and links? Select semantic space that best matches user group Warning bell for low word frequency Warning bell for low term vector Before computing similarity, simulate human elaboration of link texts during comprehension, using LSA Near neighbors, finding terms simultaneously familiar and similar in meaning Compute goal-heading and goal-link similarity with LSA cosines, defining weak scent as a cosine <0.10, moderate scent as cosine ≥0.30

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Blackmon, Kitajima, & Polson, CHI2005 25/26 Conclusions: Extending CWW successful for research and development of tool We CAN now predict severity of navigation usability problems and success rate for repairs of these problems, so we invest time to repair only what is worth repairing: tasks predicted ≥5.0 clicks Web designers using tool CAN do what unaided designers cannot: predict behavior of users different from themselves – objectively represent user diversity in education level, culture, language, and field of expertise (background knowledge)

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Blackmon, Kitajima, & Polson, CHI2005 26/26 Conclusions, continued Scales up to large websites Reliable (LSA measures vs. human judgments) Psychologically valid (228-task dataset, large n gives stable mean for each task), based on cognitive model Theory matters Drives experimental design High accuracy and psychological validity of tool Practitioners and researchers can now put the tool to use with trust

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Blackmon, Kitajima, & Polson, CHI2005 27/26

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Blackmon, Kitajima, & Polson, CHI2005 28/26 Non-problem task Find Fern approaches asymptote of pure forward search One-click minimum path for both problems AND non-problems 1.1 mean total clicks on links 90% pure forward search (minimum path solution) 97% of first clicks were on link under correct heading 100% success rate -- everyone finished task in 1 or 2 clicks 9 seconds = mean solution time

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