Chp.9 Evaluation.pdf

# HUMAN-COMPUTER INTERACTION ## Chapter 9: HCI Evaluation Techniques ### Evaluation - tests usability and functionality of a system - occurs in laboratory, field and/or in collaboration with users - evaluates both design and implementation - should be considered at all stages in the design lifecycl...

# HUMAN-COMPUTER INTERACTION ## Chapter 9: HCI Evaluation Techniques ### Evaluation - tests usability and functionality of a system - occurs in laboratory, field and/or in collaboration with users - evaluates both design and implementation - should be considered at all stages in the design lifecycle - Formative v.s. Summative evaluation ### Goals of evaluation - assess extent of system functionality - assess effect of interface on user - identify specific problems ### 9.3 Evaluating Designs #### 9.3.1. Cognitive Walkthrough - Proposed by Polson et al. - evaluates design on how well (or easy) it supports users in learning tasks - usually performed by an expert in cognitive psychology - expert 'walks through' design to identify potential problems using psychological principles - forms used to guide analysis - **For example,** command line interface v.s. WIMP #### 9.3.2. Heuristic Evaluation - Proposed by Nielsen and 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. #### 9.3.3. Model-based evaluation - Results from the literature used to support or refute parts of design. - Care needed to ensure results are transferable to a new design. - Cognitive models used to filter design options e.g. **GOMS (goals, operators, methods, and selection)** prediction of user performance - Design rationale can also provide useful evaluation information. ### 9.4 Evaluating through user participation #### Laboratory studies - **Advantages:** - specialist equipment available - uninterrupted environment - **Disadvantages:** - lack of content - 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. #### Field Studies - **Advantages:** - natural environment - context retained (though observation may alter it) - **Disadvantages:** - distractions - noise - **Appropriate:** - Where content is crucial, and difficult to implement in a lab. ### 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 ### Experimental factors - **Subjects(participants)** - 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 ### 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, test scores. ### Variables (cont.) - **Identify IVs and DVs for each of the following research titles:** 1. The effect of animated hypermedia interfaces on student achievement of different educational objectives 2. Effects of students' prior knowledge in their ability to profit from hypermedia instruction 3. Effects of varied video gaming strategies on students' attitudes. ### Hypothesis - **Prediction of outcome** - framed in terms of IV and DV - 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" ### 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. ### 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 ### Analysis of data - **What information is required?** - is there a difference? - how big is the difference? - how accurate is the estimate? ### Observational Methods - **Think Aloud** - **Cooperative evaluation** ### 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 used - **Disadvantages:** - subjective - selective - act of describing may alter task performance ### Cooperative evaluation - A 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 systems - clarification possible ### Query techniques - **Interviews** - **Questionnaires** ### Interviews - analyst questions user on a 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 ### 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 ### Questionnaires (cont.) - **Need careful design** - what information is required? - how are answers to be analyzed? - **Styles of question:** - general - open ended - scalar - multi-choice - ranked