1. 1 Human-Computer Interaction Usability Specifications

2. 2 Lecture Overview Definition and purposeDefinition and purpose Usability factorsUsability factors Measuring instrumentsMeasuring instruments Usability specification processUsability specification process Setting usability levelsSetting usability levels Advantages and disadvantagesAdvantages and disadvantages

3. 3 ISO 9241 Usability Definition (1990) ‘‘The effectiveness, efficiency and satisfaction with which specified users can achieve specified goals in a particular environment.”

4. 4 Functional and Usability Specifications Functional specifications are central to ensuring system functionalityFunctional specifications are central to ensuring system functionality Usability specifications are central to ensuring system usabilityUsability specifications are central to ensuring system usability

5. 5 Purpose of Setting Usability Specifications Establish when an interface is ‘good enough’Establish when an interface is ‘good enough’ When to stop iterationWhen to stop iteration

6. 6 Common Usability Factors Speed of operationSpeed of operation Completion rateCompletion rate Error free rateError free rate Satisfaction ratingSatisfaction rating LearnabilityLearnability RetainabilityRetainability Advanced feature usageAdvanced feature usage Main software usability measures identified by IBM

7. 7 Time Dimension for Usability Factors Initial performanceInitial performance Long-term performanceLong-term performance First impressionFirst impression Long-term user satisfactionLong-term user satisfaction

8. 8 Measuring Instrument Method for providing values for a particular usability factorMethod for providing values for a particular usability factor Always quantitative (i.e. numerically measured)Always quantitative (i.e. numerically measured) ObjectiveObjective Observable user performanceObservable user performance Often associated with a benchmark test - involves typical (normally simple and frequent) task a user will performOften associated with a benchmark test - involves typical (normally simple and frequent) task a user will perform SubjectiveSubjective User opinionUser opinion Usually associated with a user questionnaireUsually associated with a user questionnaire Objective and subjective measures are equally importantObjective and subjective measures are equally important

9. 9 Usability Specification Process Defining usability through metricsDefining usability through metrics Setting and agreeing planned levels of metricsSetting and agreeing planned levels of metrics Analysing impact of design solutionsAnalysing impact of design solutions Incorporating user-derived feedbackIncorporating user-derived feedback Iterating until planned levels are achievedIterating until planned levels are achieved

10. 10 Usability Specification Process Usability levels become part, first of the requirements document, then of the system specification Defining usability through metricsDefining usability through metrics Setting and agreeing planned levels of metricsSetting and agreeing planned levels of metrics Analysing impact of design solutionsAnalysing impact of design solutions Incorporating user-derived feedbackIncorporating user-derived feedback Iterating until planned levels are achievedIterating until planned levels are achieved

11. 11 Sample Rows from a Usability Specification Table for DTP Package TaskIssueValue to be Measured Current Level Worst Acceptable Level Planned Target Level Best Possible Level InstallationInstallation task per benchmark number 1 Length of time to successfully install Many can’t install 25 mins15 mins10 mins Initial Performance Set a tabNumber of errors 3 errors 2 errors0 errors Initial Performance Delete a tabLength of time on first trial 6 secs 4 secs2 secs First Impression QuestionnaireAverage score (range 1-5) ??34.25

12. 12 Electronic Mail: Example Benchmark Tasks Set up parameters for two terminals (ADM3/VT100)Set up parameters for two terminals (ADM3/VT100) Set up auto-dial and auto-loginSet up auto-dial and auto-login Initiate dial-up and loginInitiate dial-up and login Start on-line usageStart on-line usage Send and receive a fileSend and receive a file Set slave printer on/offSet slave printer on/off Set up present unattended dial up/login/file transferSet up present unattended dial up/login/file transfer Read received fileRead received file Leave the systemLeave the system Note: Each task would be specified in precise detail to ensure all participants attempt exactly the same task

13. 13 Setting Levels for Usability Restrict to major / critical issuesRestrict to major / critical issues Method: guesses agreed by a teamMethod: guesses agreed by a team e.g. user interaction designer, user interface software developer, marketing person, project managere.g. user interaction designer, user interface software developer, marketing person, project manager Generates team commitment to usability targetsGenerates team commitment to usability targets Initial performance and first impression are almost always appropriateInitial performance and first impression are almost always appropriate

14. 14 Current and Worst Acceptable Levels Current LevelCurrent Level Present level of value to be measuredPresent level of value to be measured Possible even from manual system or initial prototypePossible even from manual system or initial prototype May be related to a competitive systemMay be related to a competitive system Worst Acceptable LevelWorst Acceptable Level Worst acceptable, NOT worst possibleWorst acceptable, NOT worst possible Eventually, if any observed value on any attribute does not meet this level, the system is formally unacceptableEventually, if any observed value on any attribute does not meet this level, the system is formally unacceptable Level should equal or better current level (except for initial performance - slower and error prone - make an educated guess)Level should equal or better current level (except for initial performance - slower and error prone - make an educated guess)

15. 15 Planned Target and Best Possible Levels Planned Target LevelPlanned Target Level The ‘what you would like’ levelThe ‘what you would like’ level Attributes not yet at this level focus development effortAttributes not yet at this level focus development effort Set higher than current level (if known)Set higher than current level (if known) Match or exceed competitor’s productMatch or exceed competitor’s product Best Possible LevelBest Possible Level Realistic state-of-the-art upper limitRealistic state-of-the-art upper limit Indicates room for future improvementIndicates room for future improvement Assumes expert user, best design, best available technologyAssumes expert user, best design, best available technology

16. 16 Advantages of Usability Specifications Part of the management and control mechanisms for the iterative refinement processPart of the management and control mechanisms for the iterative refinement process Define a quantitative end to the (potentially endless) iterative refinement processDefine a quantitative end to the (potentially endless) iterative refinement process Allows clear assessment of usability during iterative prototyping cyclesAllows clear assessment of usability during iterative prototyping cycles Identifies data to be collected, avoids gathering unusable or irrelevant dataIdentifies data to be collected, avoids gathering unusable or irrelevant data Objectively identifies interface weaknesses which need further design effortObjectively identifies interface weaknesses which need further design effort

17. 17 Disadvantages of Usability Specifications Measures of specific user actions in specific situationsMeasures of specific user actions in specific situations No reliable technique for setting usability specificationsNo reliable technique for setting usability specifications Different tasks and user groups may need different usability specificationsDifferent tasks and user groups may need different usability specifications

18. 18 Lecture Review Definition and purposeDefinition and purpose Usability factorsUsability factors Measuring instrumentsMeasuring instruments Usability specification processUsability specification process Setting usability levelsSetting usability levels Advantages and disadvantagesAdvantages and disadvantages