2Evaluation Techniques tests usability and functionality of systemoccurs in laboratory, field and/or in collaboration with usersevaluates both design and implementationshould be considered at all stages in the design life cycle
3Goals of Evaluation assess extent of system functionality assess effect of interface on useridentify specific problems
5Cognitive Walkthrough Proposed by Polson et al.evaluates design on how well it supports user in learning taskusually performed by expert in cognitive psychologyExpert 'walks through' design to identify potential problems using psychological principlesforms used to guide analysis
6Cognitive Walkthrough (ctd) For each task walkthrough considerswhat impact will interaction have on user?what cognitive processes are required?what learning problems may occur?Analysis focuses on goals and knowledge: does the design lead the user to generate the correct goals?
7Heuristic Evaluation Proposed by Nielsen and Molich. usability criteria (heuristics) are identifieddesign examined by experts to see if these are violatedExample heuristicssystem behaviour is predictablesystem behaviour is consistentfeedback is providedHeuristic evaluation `debugs' design.
8Review-based evaluation Results from the literature used to support or refute parts of design.Care needed to ensure results are transferable to new design.Model-based evaluationCognitive models used to filter design optionse.g. GOMS prediction of user performance.Design rationale can also provide useful evaluation information
10Laboratory studies Advantages: Disadvantages: Appropriate specialist equipment availableuninterrupted environmentDisadvantages:lack of contextdifficult to observe several users cooperatingAppropriateif system location is dangerous or impractical for constrained single user systems to allow controlled manipulation of use
11Field Studies Advantages: Disadvantages: Appropriate natural environmentcontext retained (though observation may alter it)longitudinal studies possibleDisadvantages:distractionsnoiseAppropriatewhere context is crucial for longitudinal studies
12Evaluating Implementations Requires an artefact:simulation, prototype,full implementation
13Experimental evaluation controlled evaluation of specific aspects of interactive behaviourevaluator chooses hypothesis to be testeda number of experimental conditions are considered which differ only in the value of some controlled variable.changes in behavioural measure are attributed to different conditions
14Experimental factors Subjects Variables Hypothesis Experimental design who – representative, sufficient sampleVariablesthings to modify and measureHypothesiswhat you'd like to showExperimental designhow you are going to do it
15Variables independent variable (IV) dependent variable (DV) characteristic changed to produce different conditionse.g. interface style, number of menu itemsdependent variable (DV)characteristics measured in the experimente.g. time taken, number of errors.
16Hypothesis prediction of outcome null hypothesis: framed in terms of IV and DVe.g. “error rate will increase as font size decreases”null hypothesis:states no difference between conditionsaim is to disprove thise.g. null hyp. = “no change with font size”
18Think Aloud user observed performing task user asked to describe what he is doing and why, what he thinks is happening etc.Advantagessimplicity - requires little expertisecan provide useful insightcan show how system is actually useDisadvantagessubjectiveselectiveact of describing may alter task performance
19Cooperative evaluation variation on think alouduser collaborates in evaluationboth user and evaluator can ask each other questions throughoutAdditional advantagesless constrained and easier to useuser is encouraged to criticize systemclarification possible
20Protocol analysis paper and pencil – cheap, limited to writing speed audio – good for think aloud, difficult to match with other protocolsvideo – accurate and realistic, needs special equipment, obtrusivecomputer logging – automatic and unobtrusive, large amounts of data difficult to analyzeuser notebooks – coarse and subjective, useful insights, good for longitudinal studiesMixed use in practice.audio/video transcription difficult and requires skill.Some automatic support tools available
21Automated analysis – EVA Workplace projectPost task walkthroughuser reacts on action after the eventused to fill in intentionAdvantagesanalyst has time to focus on relevant incidentsavoid excessive interruption of taskDisadvantageslack of freshnessmay be post-hoc interpretation of eventSExamplesNoldus Pocket Observer XT (http://www.noldus.com)
22Post-task Walkthroughs Transcript played back to participant for commentimmediately fresh in minddelayed evaluator has time to identify questionsuseful to identify reasons for actions and alternatives considerednecessary in cases where think aloud is not possible
24Interviewsanalyst questions user on one-to-one basis usually based on prepared questionsinformal, subjective and relatively cheapAdvantagescan be varied to suit contextissues can be explored more fullycan elicit user views and identify unanticipated problemsDisadvantagesvery subjectivetime consuming
25Questionnaires Set of fixed questions given to users Advantages quick and reaches large user groupcan be analyzed more rigorouslyDisadvantagesless flexibleless probing
26Questionnaires (ctd) Need careful design Styles of question what information is required?how are answers to be analyzed?Styles of questiongeneralopen-endedscalarmulti-choiceranked
28eye trackinghead or desk mounted equipment tracks the position of the eyeeye movement reflects the amount of cognitive processing a display requiresmeasurements includefixations: eye maintains stable position. Number and duration indicate level of difficulty with displaysaccades: rapid eye movement from one point of interest to anotherscan paths: moving straight to a target with a short fixation at the target is optimal
29physiological measurements emotional response linked to physical changesthese may help determine a user's reaction to an interfacemeasurements include:heart activity, including blood pressure, volume and pulse.activity of sweat glands: Galvanic Skin Response (GSR)electrical activity in muscle: electromyogram (EMG)electrical activity in brain: electroencephalogram (EEG)some difficulty in interpreting these physiological responses - more research needed
30Choosing an Evaluation Method when in process: design vs. implementationstyle of evaluation: laboratory vs. fieldhow objective: subjective vs. objectivetype of measures: qualitative vs. quantitativelevel of information: high level vs. low levellevel of interference: obtrusive vs. unobtrusiveresources available: time, subjects, equipment, expertise