task analysis 1 © Copyright De Montfort University 1998 All Rights Reserved Task Analysis Preece et al Chapter 7

task analysis 2 © Copyright De Montfort University 1998 All Rights Reserved User interfaces are designed for.. a new system to replace an existing manual system e.g. library information system an existing computer system being redesigned –functionality remains the same –functionality is extended or changed in some way. a completely new system with no manual equivalent (generally rare) There is usually some situation with existing users and usage that can be studied and analysed.

task analysis 3 © Copyright De Montfort University 1998 All Rights Reserved Task Analysis provides an essential basis for –early stages of interface design –evaluation of design at early and late stages –structuring training in system use –structuring and design of documentation

task analysis 4 © Copyright De Montfort University 1998 All Rights Reserved Task Analysis Techniques HTA – This and other related techniques focus on what actually happens, rather than what should happen –Eg Obtaining a balance from an ATM Cognitive task analysis. This technique aims to describe some of the cognitive characteristics of users tasks. –Eg The time to recognise interpret and respond to an on-screen instruction

task analysis 5 © Copyright De Montfort University 1998 All Rights Reserved Levels of Task Analysis relate to existing situation or new system. General Analysis of User Characteristics Detailed Analysis of tasks in present job(s) Subset of tasks to be included in new system Analysis of Actions and Objects in new system

task analysis 6 © Copyright De Montfort University 1998 All Rights Reserved General Analysis level who are the users –classify the users into one or more groups –define characteristics of the group what are the main task components of the users’ present job –what proportion of time is spent in different tasks –what causes variations in this where are the tasks carried out what equipment (other than the computer system) are used what communication is there between the user and other people

task analysis 7 © Copyright De Montfort University 1998 All Rights Reserved Detailed analysis of tasks in present job what is the hierarchical structure of main tasks, and subtasks within these main tasks how do users see the structure of their job in terms of tasks for each task identified –what information is required –what actions arise or result from decisions –what feedback is provided on effect of actions –what affects successful performance –what are the possible errors and what factors cause these

task analysis 8 © Copyright De Montfort University 1998 All Rights Reserved Detailed analysis of tasks in present job what are the good features of the existing system which should be retained in the subsequent redesign what are the bad features of the existing system that should be designed out what skills are required for each task how are the required skills trained initially and how are these retained

task analysis 9 © Copyright De Montfort University 1998 All Rights Reserved Objectives of task analysis to support interface design identify a hierarchy of user goals, tasks and subtasks together with a plan describing how and when these are done represent lowest level task as a set of procedures –include statements of information requirements and exception conditions identify set of actions and associated objects

task analysis 10 © Copyright De Montfort University 1998 All Rights Reserved Requirements for a task analysis method a structure to represent goals, subtasks, procedures, objects and actions a means of collecting data from experts in the task domain a means of representing the analysis to –check validity of the analysis back with experts –communicate with others in design team guidance for mapping the analysis to the design

task analysis 11 © Copyright De Montfort University 1998 All Rights Reserved Hierarchical task analysis (HTA) Structural components goal - statement of a desired state to be achieved –e.g. obtain a bank account balance operation - things done in order to achieve goals –e.g. produce a paper copy showing current balance sub-operations- subordinate operations to attain main operation plan - specifies when the conditions when each sub- operation will be carried out

task analysis 12 © Copyright De Montfort University 1998 All Rights Reserved Hierarchical task analysis (HTA) Originally devised to define training requirements in process industry - method needs additionally –descriptions of information requirements for lowest level sub-operations –dictionary of objects and associated actions Representation –tree diagram or tabular format Advantages of HTA –simple, informal notation –but still requires considerable skills on part of analyst.

task analysis 13 © Copyright De Montfort University 1998 All Rights Reserved Relating the model to interface requirements Errors in performance can result from: some information –not available when required –available but not sufficiently accurate –available and accurate, but not correctly perceived user’s knowledge of task goal incomplete insufficient or delayed feedback user’s ability to formulate correct decision is inadequate delay in being able to communicate decision to rest of system

task analysis 14 © Copyright De Montfort University 1998 All Rights Reserved Implications for interface design when a task has to be performed ensure that the necessary information is available –so for each task supported by the interface, what information is required? user decisions need to be communicated quickly to the system –so for each task, how will the user input decisions? feedback on task performance should be available –so for each task, how will feedback information be presented and what form should this take?

task analysis 15 © Copyright De Montfort University 1998 All Rights Reserved Means of collecting task analysis data interviews with potential users observations of users performing tasks by trained observers activity sampling activity logging (by observer) activity logging (by user) - 'diary of activities‘

task analysis 16 © Copyright De Montfort University 1998 All Rights Reserved Further Reading