1. Department of CSE, KLU 1 Chapter 9 evaluation techniques

2. Department of CSE, KLU 2 9.1 Evaluation Techniques We have already discussed a design process to support the design of usable interactive systems. The role of evaluation is to assess our designs and test our systems to ensure that they actually behave as we expect and meet user requirements. Evaluation should occur throughout the design life cycle, with the results of the evaluation feeding back into modifications to the design. Analytic and informal techniques can and should be used. So that the problems can be ironed out before implementation itself: it is much easier to change a design in the early stages of development than in the later stages. Types of evaluation: evaluation by the designer or by a usability expert, without direct involvement by users-  useful for assessing early designs and prototypes user participation. evaluation that studies actual use of the system-  normally requires a working prototype or implementation. expert analysis

3. Department of CSE, KLU 3 9.2 Goals of Evaluation Evaluation has three main goals: 1.to assess the extent and accessibility of the system’s functionality The design of the system should make the appropriate functionality available within the system, but making it clearly reachable by the user. It also involves matching the use of the system to the user’s expectations of the task. Evaluation at this level may also include measuring the user’s performance with the system. 2.to assess users’ experience of the interaction This includes considering aspects such as how easy the system is to learn, its usability and the user’s satisfaction with it. It may also include his enjoyment and emotional response. It is important to identify areas of the design that overload the user in some way. 3.to identify any specific problems with the system. These may be aspects of the design which, when used in their intended context, cause unexpected results, or confusion amongst users. This is, of course, related to both the functionality and usability of the design. It is specifically concerned with identifying trouble-spots which can then be rectified.

4. Department of CSE, KLU 4 9.3 Evaluation through expert analysis Cognitive Walkthrough Heuristic Evaluation Model based evaluation Using previous studies in evaluation

5. Department of CSE, KLU 5 9.3.1 Cognitive Walkthrough Proposed by Polson et al. –evaluates design on how well it supports user in learning task –usually performed by expert in cognitive psychology –expert ‘walks through’ design to identify potential problems using psychological principles –forms used to guide analysis

6. Department of CSE, KLU 6 Cognitive Walkthrough... To do a walkthrough (cognitive walkthrough), you need four things: 1.A specification or prototype of the system. It doesn’t have to be complete, but it should be fairly detailed. 2.A description of the task the user is to perform on the system. 3.A complete, written list of the actions needed to complete the task with the proposed system. 4.An indication of who the users are and what kind of experience and knowledge the evaluators can assume about them.

7. Department of CSE, KLU 7 Cognitive Walkthrough... The evaluators try to answer the following four questions for each step in the action sequence. 1.Is the effect of the action the same as the user’s goal at that point? 2.Will users see that the action is available? 3.Once users have found the correct action, will they know it is the one they need? 4.After the action is taken, will users understand the feedback they get?

8. Department of CSE, KLU 8 Cognitive Walkthrough... For each task walkthrough considers –what 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?

9. Department of CSE, KLU 9 9.3.2 Heuristic Evaluation Proposed by Jakob Nielsen and Rolf Molich. usability criteria (heuristics) are identified design examined by experts to see if these are violated Example heuristics –system behaviour is predictable –system behaviour is consistent –feedback is provided Heuristic evaluation `debugs' design.

10. Department of CSE, KLU 10 Heuristic Evaluation... Heuristic evaluation, developed by Jakob Nielsen and Rolf Molich, is a method for structuring the critique of a system using a set of relatively simple and general heuristics. Heuristic evaluation can be performed on a design specification so it is useful for evaluating early design. It can also be used on prototypes, storyboards and fully functioning systems. It is a flexible, relatively cheap approach. It is often considered a discount usability technique. The general idea behind heuristic evaluation is that 3 to 5 evaluators independently critique a system to come up with potential usability problems. Each evaluator assesses the system and notes violations of any of the heuristics that would indicate a potential usability problem. The severity of each usability problem is assessed based on four factors: how common is the problem, how easy is it for the user to overcome, will it be a one-off problem or a persistent one, and how seriously will the problem be perceived?

11. Department of CSE, KLU 11 Heuristic Evaluation... Nielsen’s ten heuristics are: 1.Visibility of system status 2.Match between system and the real world 3.User control and freedom 4.Consistency and standards 5.Error prevention 6.Recognition rather than recall 7.Flexibility and efficiency of use 8.Aesthetic and minimalist design 9.Help users recognize, diagnose and recover from errors 10.Help and documentation

12. Department of CSE, KLU 12 9.3.3. Model-based evaluation A third expert-based approach is the use of models. Certain cognitive and design models provide a means of combining design specification and evaluation into the same framework. For example, the GOMS (goals, operators, methods and selection) model predicts user performance with a particular interface and can be used to filter particular design options. Similarly, lower- level modeling techniques such as the keystroke-level model provide predictions of the time users will take to perform low-level physical tasks. Design methodologies, such as design rationale, also have a role to play in evaluation at the design stage. Dialog models can also be used to evaluate dialog sequences for problems, such as unreachable states, circular dialogs and complexity.

13. Department of CSE, KLU 13 9.3.4. Using previous studies in evaluation A final approach to expert evaluation exploits inheritance, using previous results as evidence to support (or refute) aspects of the design. It is expensive to repeat experiments continually and an expert review of relevant literature can avoid the need to do so. The experimental results cannot be expected to hold arbitrarily across contexts. The reviewer must select evidence carefully, noting the experimental design chosen, the population of participants used, the analyses performed and the assumptions made. The review should take account of both the similarities and the differences between the experimental context and the design under consideration. This is why this is an expert review: expertise in the area is required to ensure that correct assumptions are made.

14. Department of CSE, KLU 14 Testing with actual users include empirical or experimental methods, observational methods, query techniques, and methods that use physiological monitoring, such as eye tracking and measures of heart rate and skin conductance. User participation in evaluation tends to occur when there is at least a working prototype of the system in place. Styles of evaluation Two distinct evaluation styles: those performed under laboratory conditions and those conducted in the work environment or ‘in the field’. 9.4 Evaluation through user Participation

15. Department of CSE, KLU 15 Laboratory studies. Advantages: –specialist equipment available –uninterrupted environment Disadvantages: –lack of context –difficult to observe several users cooperating Appropriate –if system location is dangerous or impractical for constrained single user systems to allow controlled manipulation of use 9.4 Evaluation through user Participation

16. Department of CSE, KLU 16 Field Studies It takes the designer or evaluator out into the user’s work environment in order to observe the system in action. Advantages: –natural environment –context retained (though observation may alter it) –longitudinal studies possible Disadvantages: –distractions –noise Appropriate –where context is crucial for longitudinal studies

17. Department of CSE, KLU 17 Evaluating Implementations Requires an artefact: simulation, prototype, full implementation

18. Department of CSE, KLU 18 Experimental evaluation controlled evaluation of specific aspects of interactive behaviour evaluator chooses hypothesis to be tested a 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

19. Department of CSE, KLU 19 Experimental factors Subjects –who – representative, sufficient sample Variables –things to modify and measure Hypothesis –what you’d like to show Experimental design –how you are going to do it

20. Department of CSE, KLU 20 Variables independent variable (IV) characteristic changed to produce different conditions e.g. interface style, number of menu items dependent variable (DV) characteristics measured in the experiment e.g. time taken, number of errors.

21. Department of CSE, KLU 21 Hypothesis prediction of outcome –framed in terms of I.V. and D.V. e.g. “error rate will increase as font size decreases” null hypothesis: –states no difference between conditions –aim is to disprove this e.g. null hyp. = “no change with font size”

22. Department of CSE, KLU 22 Experimental design within groups design –each subject performs experiment under each condition. –transfer of learning possible –less costly and less likely to suffer from user variation. between groups design –each subject performs under only one condition –no transfer of learning –more users required –variation can bias results.

23. Department of CSE, KLU 23 Analysis of data Before you start to do any statistics: –look at data –save original data Choice of statistical technique depends on –type of data –information required Type of data –discrete - finite number of values –continuous - any value

24. Department of CSE, KLU 24 Analysis - types of test parametric –assume normal distribution –robust –powerful non-parametric –do not assume normal distribution –less powerful –more reliable contingency table –classify data by discrete attributes –count number of data items in each group

25. Department of CSE, KLU 25 Analysis of data... What information is required? –is there a difference? –how big is the difference? –how accurate is the estimate? Parametric and non-parametric tests mainly address first of these

26. Department of CSE, KLU 26 Experimental studies on groups More difficult than single-user experiments Problems with: –subject groups –choice of task –data gathering –analysis

27. Department of CSE, KLU 27 Subject groups larger number of subjects  more expensive longer time to `settle down’ … even more variation! difficult to timetable so … often only three or four groups

28. Department of CSE, KLU 28 The task must encourage cooperation perhaps involve multiple channels options: –creative task e.g. ‘write a short report on …’ –decision games e.g. desert survival task –control task e.g. ARKola bottling plant

29. Department of CSE, KLU 29 Data gathering several video cameras + direct logging of application problems: –synchronisation –sheer volume! one solution: –record from each perspective

30. Department of CSE, KLU 30 Analysis N.B. vast variation between groups solutions: –within groups experiments –micro-analysis (e.g., gaps in speech) –anecdotal and qualitative analysis look at interactions between group and media controlled experiments may `waste' resources!

31. Department of CSE, KLU 31 Field studies Experiments dominated by group formation Field studies more realistic: distributed cognition  work studied in context real action is situated action physical and social environment both crucial Contrast: psychology – controlled experiment sociology and anthropology – open study and rich data

32. Department of CSE, KLU 32 9.4.3 Observational Methods Think Aloud and Cooperative evaluation Protocol analysis Automated analysis Post-task walkthroughs

33. Department of CSE, KLU 33 Think Aloud user observed performing task user asked to describe what he is doing and why, what he thinks is happening etc. Advantages –simplicity - requires little expertise –can provide useful insight –can show how system is actually use Disadvantages –subjective –selective –act of describing may alter task performance

34. Department of CSE, KLU 34 Cooperative evaluation variation on think aloud user collaborates in evaluation both user and evaluator can ask each other questions throughout Additional advantages –less constrained and easier to use –user is encouraged to criticize system –clarification possible

35. Department of CSE, KLU 35 Protocol analysis paper and pencil – cheap, limited to writing speed audio – good for think aloud, difficult to match with other protocols video – accurate and realistic, needs special equipment, obtrusive computer logging – automatic and unobtrusive, large amounts of data difficult to analyze user notebooks – coarse and subjective, useful insights, good for longitudinal studies Mixed use in practice. audio/video transcription difficult and requires skill. Some automatic support tools available

36. Department of CSE, KLU 36 automated analysis EVA Experimental Video Annotator Workplace project Post task walkthrough –user reacts on action after the event –used to fill in intention Advantages –analyst has time to focus on relevant incidents –avoid excessive interruption of task Disadvantages –lack of freshness –may be post-hoc interpretation of events

37. Department of CSE, KLU 37 post-task walkthroughs transcript played back to participant for comment –immediately  fresh in mind –delayed  evaluator has time to identify questions useful to identify reasons for actions and alternatives considered necessary in cases where think aloud is not possible

38. Department of CSE, KLU 38 9.4.4 Query Techniques Interviews Questionnaires

39. Department of CSE, KLU 39 Interviews analyst questions user on one-to -one basis usually based on prepared questions informal, subjective and relatively cheap Advantages –can be varied to suit context –issues can be explored more fully –can elicit user views and identify unanticipated problems Disadvantages –very subjective –time consuming

40. Department of CSE, KLU 40 Questionnaires Set of fixed questions given to users Advantages –quick and reaches large user group –can be analyzed more rigorously Disadvantages –less flexible –less probing

41. Department of CSE, KLU 41 Questionnaires... Need careful design –what information is required? –how are answers to be analyzed? Styles of question –general –open-ended –scalar –multi-choice –ranked

42. Department of CSE, KLU 42 9.4.5 Physiological methods Eye tracking Physiological measurement

43. Department of CSE, KLU 43 eye tracking head or desk mounted equipment tracks the position of the eye eye movement reflects the amount of cognitive processing a display requires measurements include –fixations: eye maintains stable position. Number and duration indicate level of difficulty with display –saccades: rapid eye movement from one point of interest to another –scan paths: moving straight to a target with a short fixation at the target is optimal

44. Department of CSE, KLU 44 physiological measurements emotional response linked to physical changes these may help determine a user’s reaction to an interface measurements 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

45. Department of CSE, KLU 45 9.5 Choosing an Evaluation Method when in process:design vs. implementation style of evaluation:laboratory vs. field how objective:subjective vs. objective type of measures:qualitative vs. quantitative level of information:high level vs. low level level of interference:obtrusive vs. unobtrusive resources available:time, subjects, equipment, expertise