Task Analysis and Usability Analysis of a Ticket Machine

Research Paper (undergraduate) 2008 8 Pages




This report examines the car park ticket machine (TM). The Hierarchical Task Analysis (HTA; Sheperd, 2000; cited in Mills, 2007) is used as a framework: Firstly, psychological issues related to using the TM are discussed. Secondly, an usability analysis of the TM is conducted, whereupon principles of usability (Jordan, 1998) are applied. The result is that the design has major issues. Subsequently, an improved design is sketched out - considering identified issues. Finally, an evaluation method for the redesign is introduced.

Hierarchical Task Analysis

Mills (2007, p.501) reported the HTA belongs to “task description methods, focusing on crucial aspects of the task within the context of the overall task”. The overall goal ‘use the ticket machine’ was broken down into five subordinate operations, which are used as a framework for a cognitive walkthrough (cp. Connell, Blandford & Green, 2004).

(1) Read instructions
(2) Enter registration number
(3) Pay
(4) Press green button
(5) Take ticket

Psychological Issues and Usability Analysis

Psychological Issues. Positioning ‘using the TM’ in a psychological context, the following factors are examined to predict pertinent issues.

1. Information processing (Wickens, 1992): perception (top-down cognition), attention (selective / divided), and memory (long-term / short-term).

2. Psychosocial factors: stress[1], frustration[2], and motivation[3].

Usability Analysis. Usability is defined as “the effectiveness, efficiency and satisfaction with which specified users can achieve goals in a particular environment” (ISO9241). Jordan (1998) postulated ten principles of usability[4], which are used to assess the TM.

1. Read instructions

Psychological issues.

- Information processing
- Selective attention / top down cognition required to find information o Short-term memory (STM) capacity is exceeded: there are more than 7+-2 chunks
- Psychosocial factors
- Stressed users (e.g. in a queue) understand instructions less o Frustration: reading a long instruction blocks user from getting the ticket o Motivation drops, because instructions are not straightforward

Usability issues.

- Not compatible with user resources: contains too much information
- No visual clarity: Insufficient and confusing structure.
- No prioritizing: Important information is not accessible, e.g. via headlines.

2. Enter registration number

Psychological issues.

- Information processing
- Top-down cognition / selective attention required to find small number-pad o Long-term memory (LTM). Conceptual model of number-pad is not confirm with present number-pad
- Psychosocial factors
- Stressed users (e.g. time pressure) are expected to have more problems. o Frustration arises / motivation drops, because this subtask costs a lot of time and cognitive resources

Usability issues

- TM does not prevent errors, e.g. wrong number entered
- No user control, e.g. enter registration number again
- Display not compatible with conceptual model, e.g. ‘enter’ cp. PC keyboard
- Does not satisfy user’s resources: number-pad too small
- No cue of function, i.e. show that number-pad is available (e.g. illumination)

3. Pay

Psychological issues.

- Information processing
- Divided attention: user must do many things at the same time (e.g. in his wallet, at display)
- LTM. Errors might result from activation of a general schema, i.e. normally TMs give change
- Psychosocial factors
- Frustration, because user still has not got the ticket
- User might get angry (frustration-aggression theory, cp. Zimbardo & Gerrig, 1999)
- Motivation drops, because getting the ticket is complicated Usability issues
- User resources (memory) not considered: e.g. remind “no change given”
- No cue of function (explicitness), e.g. illuminate ‘coin slot’ if active
- No user control, i.e. go back to ‘enter registration number’

4. Press green button

Psychological issues.

- Information processing
- Top-down cognition necessary to find buttons
- Divided attention, e.g. monitor display and press buttons at the same time o LTM: Errors result from activation of a general schema of a TM. Disturbance, because there are two buttons.
- Psychosocial factors: Frustration, because of confusion (two buttons) blocks user Usability issues
- No user control, i.e. go back to ‘pay’
- Explicitness: does not make options visible: e.g. ‘press green button’
- Compatibility with conceptual model: user would expect only one button, but there are two

5. Take ticket

Psychological issues.

- Information processing: Top-down cognition, e.g. visual search for ticket collection tray Usability issues.
- Compatibility with expectations: ticket collection tray is hardly visible

Summary of main issues

Psychological issues. The TM design exceeds the users’ information procession capacity in terms of perception, attention and memory (Wickens, 1992). Cognitive load (Sweller, 1988) is high, because the cognitive resources must deal with a lot of work. Cognitive characteristics are not considered sufficiently. The major issue is frustration: Users feel blocked from getting the ticket, because there are too many problems / obscurities.

Usability issues. Major issues are the incompatibility of the design with users’ expectations and conceptual models. Furthermore, the TM does not consider user resources, feedback, user control, and does not give enough cues.

Improved ticket machine design

The TM redesign results from four the four principles of layout design: (1) importance, (2) frequency of use, (3) sequence of use, and (4) functionality. Its objective is to match the TM to the user[5].

(1) Importance

The display / menu is the most important control. Therefore, it was placed at face level (perception), which is a convenient location. It enables to follow the state of processing (feedback), gives cues, and redundantises the instructions. Users can actively control the process by going backward/forward with arrow keys (user control).

(2) Frequency of use

The display is also the most frequently used control. It minimises physical movement, workload and visual search.

(3) Sequence of use


[1] Stress is discussed regarding to the Yerkes-Dodson law (Matthews, Davies, Westerman & Stammers, 2000), which establishes a relationship between mental arousal and performance.

[2] Frustration occurs when one is blocked from reaching a goal, i.e. getting the ticket (Zimbardo & Gerrig, 1999).

[3] Motivation is seen in terms of expectancy of success (Matthews et al., 2000): beliefs that a goal is not

attainable decrease motivation.


Consistency, compatibility, user resources, feedback, prevent errors, user control, visual clarity, prioritize, appropriate use of technology, and explicitness.

[5] Examples for the considered usability principles are denoted in brackets.


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University of Derby – Institut für Psychologie
Hierarchical Task Analaysis Usability Analysis Ticket Machine

Title: Task Analysis and Usability Analysis of a Ticket Machine