Aims of this chapter Describe the important concepts associated with inspection methods Show how heuristic evaluation can be adapted to evaluate different types of interactive products Explain what is involved in doing heuristic evaluation and various kinds of walkthrough Describe how to perform two types of predictive techniques, GOMS and Fitts Law, and when to use them Discuss the advantages and disadvantages of using analytical evaluation Summary Inspections: Heuristic Evaluations Heuristic evaluation is a usability technique in which experts guided by a set of usability principles known as heuristics evaluate whether user interface elements such as dialog boxes, menus, conform to the principles. Some of the usability principles included
Visibility of system status Match between system and the real world User control and freedom Consistency and standards Error prevention Recognition rather than recall Flexibility and efficiency of use Aesthetic and minimalist design Help users recognize, diagnose, and recover from errors Help and documentation Doing heuristic evaluation has three stages
Briefing session Evaluation period Debriefing session Inspection: Walkthroughs Cognitive Walkthroughs
Cognitive walkthroughs involve simulating a user’s problem-solving process at each step in the human-computer dialog.
They focus on evaluating designs for ease of learning. The steps involved in cognitive walkthroughs are…
1) The characteristics of typical users are identified and documented and sample tasks are developed that focus on the aspect of the design that will be evaluated.
2) A designer or one or more evaluators come together to do the walkthrough
3) The evaluators walk through the action sequences for each task with a focus on the following..
- Will the correct action be sufficiently evident to the user
- Will the user notice that the correct action is available
-
Will the user associate and interpret the response from the action correctly 4) As the walkthrough is being done a record of critical information is compiled in which
- The assumptions about what would cause problems are recorded
- Notes about side issues and design changes are made
- A summary of results is compiled 5) The design is then revised to fix the problem presented
Pluralistic walkthroughs
Pluralistic walkthroughs are a type of walkthrough in which users, developers and usability experts work together to step through a task scenario, discussing usability issues associated with dialog elements involved in the scenario steps. Each group of experts is asked to assume the role of a user. The walkthroughs are then done following a series of steps…
Scenarios are developed in the form of a series of hardcopy screens representing a single path through the interface. The scenarios are presented to the panel of evaluators and the panellists are asked to write down the sequence of actions they would take to move from one screen to another. They do this individually without conferring. When everyone has written down their actions, the panellists discuss the actions that they suggested for that round of review Then the panel moves on to the next round of screen. This process continues until all the scenarios have been evaluated. Some benefits include…
Strong focus on users tasks at a detailed level Lends well to participatory design practices Limitations include…
expensive having to get a group of experts together slow rate of progress major time constraints Predictive models The GOMS model
Acronym stands for Goals, operators, methods and selection rules Description of each section below…
Goals – particular state the user wants to achieve Operators – cognitive process and physical actions that need to be performed in order to attain those goals Methods – learned procedures for accomplishing the goals Selection rules – determine which method to select when there is more than one available for a given stage of a task Benefits of GOMS
Allows comparative analyses to be performed for different interfaces, prototypes, or specifications Limitations of GOMS
Has a highly limited scope Intended to be used only to predict expert performance does not allow for errors to be modelled can only make predictions about predictable behaviour The keystroke level model
The keystroke level model differs from GOMS model in that it provides actual numerical predictions of user performance. Tasks can be compared in terms of the time it takes to perform them when using different strategies. The main benefit of making these kinds of quantitative predictions is that different features of systems and applications can be easily compared to see which might be the most effective performing specific kinds of tasks.
The predicted time it takes to execute a given task is calculated by describing the sequence of actions involved and then summiung together the approximate times that each one will take.
Fitt’s Law
Fitt’s law predicts the time it takes to reach a target using a pointing device. In ID it is used to describe the time it takes to point at a target based on the size of the object and the distance to the object.
In a nutshell the bigger the target the easier and quicker it is to reach it.
Fitt’s law also predicts that the most quickly accessed targets on any computer display are the four corners of the screen.
