1. 1http://img.cs.man.ac.uk/stevens Evaluation CS2391 Lecture n+1: Robert Stevens

2. 2http://img.cs.man.ac.uk/stevens Introduction You’ve gathered requirements, designed your system, built the artefact, …But does it fulfil the user‘s requirements? Basic usability Basic evaluation Evaluation styles Design evaluation Implementation evaluation

3. 3http://img.cs.man.ac.uk/stevens Usability Basics Allowing users to achieve a goal with efficiency, effectiveness and satisfaction Utility is the functionality of a system Utility without usability, but not vice versa Worthy, but unhelpful Have paradigms of good usability, e.g. GUI Also need theory to know why something is usable Really want principles to guide developers – engineering not craft

4. 4http://img.cs.man.ac.uk/stevens Execution and Evaluation SystemUser Input Output presentation performance observation articulation

5. 5http://img.cs.man.ac.uk/stevens Execution & Evaluation (2) Presentation: How the system renders state and allows the user to evaluate state and alteration to the state Observation: What the user notices of the presentation; Can he/she see what they need to? Articulation: Expression of a user’s execution plan Performance: the system’s execution of a plan, the results of which are presented to the user

6. 6http://img.cs.man.ac.uk/stevens Usability Principles a.Visibility of system status System should always keep users informed b.Match between system and the real world System should speak the user's language c.System functions chosen by mistake need a clear 'emergency exit' d.Consistency and standards Avoid ambiguity e.Error prevention f.Recognition rather than recall g.Flexibility and efficiency of use h.Aesthetic and minimalist design i.recognize, diagnose and recover from errors j.Help and documentation

7. 7http://img.cs.man.ac.uk/stevens What is Evaluation? Do the design and implementation behave as we expect and fulfil the user’s requirements? Not just an add on at the end! Assess the design at various times during the life cycle Assess implementation prototypes, alpha and beta versions Evaluation saves time and money Many types of evaluation and the trick is to choose the appropriate one Purpose is to uncover usability problems

8. 8http://img.cs.man.ac.uk/stevens Usability Thoughts Recall and recognition Making a system easier to use makes it more powerful Humans can switch topics fast – think of more than one thing at once Computer system should be able to do the same Complex syntax often hides the task – need directness of interaction

9. 9http://img.cs.man.ac.uk/stevens Styles of Evaluation Evaluation Design Evaluation Cognitive walkthrough Heuristic evaluation Review-based evaluation The use of models Implementation Evaluation Empirical Observational Query

10. 10http://img.cs.man.ac.uk/stevens Evaluation Styles (2) Cheaper to evaluate design, before the expense of implementation Tends not to involve the end-users, except as consultants Evaluation of an implementation does involve end-users Design evaluation techniques can be used to evaluate implementation The former are often paper based and involve experts The latter are time consuming, difficult and expensive and can involve numbers of end-users

11. 11http://img.cs.man.ac.uk/stevens Types of User Not all users are Computer Scientists Different users have different needs Remember: Managers, system administrators and trainers Use end-users where possible and appropriate Important to have evaluatees that are representative of end- users Balance between under use and over use: Users need a reward for their time

12. 12http://img.cs.man.ac.uk/stevens Hawthorn Effect Users like to please the evaluator People respond well to having someone interested in them Simply by evaluating an artefact, experience of that artefact improves Investigation of light levels in factories showed the investigation itself was the most important factor Not much to be done about it – be aware

13. 13http://img.cs.man.ac.uk/stevens Goals of Evaluation Does the system have the correct functionality? Does it match the users task? A clerk used to searching by post-code, should be able to search by post-code Can the functionality be used: What is the effect on the user? What are the problems with the system? The last is part of the other two, but negative aspects drawn out

14. 14http://img.cs.man.ac.uk/stevens Laboratory Techniques A usability lab: One way mirror; Video and audio recorders Logging of system Lacks context; unnatural for end-users and natural collaborative work difficult Does allow close study, particularly of specialist task or particular UI notion Good for single user tasks

15. 15http://img.cs.man.ac.uk/stevens Field Techniques See the user in context Allows a user to interact with all people, objects and actions involved in a task Collaborative work can take place Noisy, difficult to record, etc Can lack detail possible in laboratory

16. 16http://img.cs.man.ac.uk/stevens Cognitive Walk Through Bring psycology theory into informal and subjective walk through 1.Need a design: not necessarily complete, but location and wording helpful 2.A description of the task: Should be representative 3.A list of actions the user makes to perform the task 4.A description of the users and the experience expected of them given to experts, who step through actions and make an assessment of usability 1.Are the users performing the task described by the action? 2.Can the users see the object of interaction (button etc)? 3.Can the user tell that it is the right action? 4.Once performed, does the user get appropriate feedback? End of execution & evaluation cycle

17. 17http://img.cs.man.ac.uk/stevens Heuristic Evaluation A set of heuristics (rules of thumb) developed by Jakob Nielsen and Rolf Molich Each heuristic used to critique an interface A set of independent experts use the heuristics Problems found following a Poisson distribution – 5 experts find about 75% of problems Usability questions used to guide and stimulate Essentially a check list

18. 18http://img.cs.man.ac.uk/stevens Review Based Evaluation Principles from experimental psychology and HCI literature used to provide evaluation criteria E.g., menu design, naming items, icon design and language design and memory attributes Cheaper than performing the experiment, but beware of context in which a study was performed Like all expert based methods, it is all about stimulating basic questions to be asked Try and ensure independence of experts Performance, using scales and comment fields should be used

19. 19http://img.cs.man.ac.uk/stevens Empirical Evaluation Evaluating the implementation (can also use Design Evaluation methods here) Empirical studies concentrate on end-users, rather than experts The controlled experiment technique Measure some attribute, while controlling other attributes of system Various experimental conditions, which differ only in the value of some variable Independent (manipulated) and dependent (measured) variable Difference in behaviour attributed to different values of independent variable that provide the different conditions (interface style, pointing device, wording, etc.) Dependent variable must be measurable in some way – speed, mouse clicks, satisfaction etc. Use both subjective and objective Measures

20. 20http://img.cs.man.ac.uk/stevens Empirical Techniques (2) A hypothesis is framed in terms of the variables A change in the independent variable causes a change in the dependent The experiment attempts to prove this relationship Achieved by disproving null hypothesis; that is, no relationship of variables Use statistics to show that any differences seen could not have happened by chance Experimental design: Between groups and within groups Between Groups: Subjects assigned to experimental and control groups; latter ensures it is the independent variable that counts Each subject only does one condition, so avoiding learning effects; but prone to variation Within Groups: Subject performs in all conditions; Vary condition order to avoid learning

21. 21http://img.cs.man.ac.uk/stevens Empirical Evaluation (3) Good for evaluation of individual design decisions: Colour, dialogue, wording, etc. Less good for overall usability – systems and humans too complex for controlled experiment Difficult to design Expensive in time, money and users

22. 22http://img.cs.man.ac.uk/stevens Observational Techniques Think aloud & Co-operative evaluation Observing the user’s actions in work context – the whole task Usually pre-determined, representative tasks and users explain what they are doing (think aloud) Experimenter interacts with participant (subject) to elicit more information Everything recorded (notes, system log, audio, video) Protocols analysed Post-experiment walk through

23. 23http://img.cs.man.ac.uk/stevens Query Based Techniques Ask the user can be very informative Simple, but highly subjective Interviews and questionnaires (see earlier lectures) Good for large numbers and high-level Good for exploring alternative strategies, particularly in context Less systematic, more subjective

24. 24http://img.cs.man.ac.uk/stevens Summary Need to test appropriateness of functionality Also that functionality can be used Efficiency, effectiveness and satisfaction Evaluation of design and its implementation Choose your users with care HCI: Dix, Findlay, Abowd & Beale; Chapter 11