Design is by far the cheapest and most effective way for a system to benefit from paying attention to human factors. If a system delivers exactly the results required of it by an organisation; this represents a happy convergence of user requirements, designers’ intentions and practical implementation.
Benefits of a user-centred design approach
A user-centred design approach should be adopted for the following reasons:
- Both individual users and the organisation as a whole will perform better if users are involved in the design of their equipment, tools and working environments.
- Involving users in evaluating the design product at an early stage in the design process will help to ensure that the product is best suited to its purpose. It will also minimise the time, effort and costs associated with making subsequent design changes.
- Once a system is being used, correcting a problem can cost an estimated 10 times more than fixing it during design (can cost 100 times more).
For design to be both user-centred and sound, the design team must ensure that:
- The end users (those who will use the product) take part in the design process.
- Data on the needs of all types of user (all stakeholders) is collected and analysed.
Impact of Poor User-Centred Design
The Three Mile Island Unit 2 reactor, near Middletown, Pennsylvania, partially melted down on March 28, 1979. This was the most serious accident in U.S. commercial nuclear power plant operating history, although its small radioactive releases had no detectable health effects on plant workers or the public. Its aftermath brought about sweeping changes involving emergency response planning, reactor operator training, human factors engineering, radiation protection, and many other areas of nuclear power plant operations. It also caused the Nuclear Regulatory Commission (NRC) to tighten and heighten its regulatory oversight. All of these changes significantly enhanced U.S. reactor safety.
One of the key causes to the accident was a poorly designed control room, specifically:
- Controls positioned too far from the instrument displays that showed the system’s condition.
- Cumbersome and inconsistent instruments that often looked identical and were placed side-by-side, even though they controlled very different functions.
- Instrument readings that were difficult to read, obscured by glare or poor lighting.
- Inconsistencies in the meaning of lights and the operation of levers or knobs. Pushing a lever up may have closed one valve, while pulling another lever down may have closed another one.
Figure 1. Three Mile Island nuclear accident
Design and User Requirements
Designers need to distinguish between three different types of user requirements.
- The first type is to do with user aims. Designers must understand what users need the product for, and how these needs fit with their general workflow and that of the organisation as a whole.
- The second is to do with user characteristics. This means that designers must understand what the human performance capabilities, limitations and expectations of the users are, including: extent and regularity of system use; experience with similar equipment; user stereotypes and expectations of what the product is for and how it works; and expected maintenance schedules and required levels of maintainer expertise.
- The third type of user requirement is to do with user values. If a new piece of technology is to be successfully adopted, it must take account of what motivates users and what can just as easily turn them off.
Techniques for usability testing
In practice it is exceedingly difficult for designers to know or imagine all the usability criteria that are important to users. Therefore it is so important to collect feedback from users as part of an ongoing process to improve the operability and maintainability of the product. Among many techniques for usability testing are:
- Think-aloud techniques – the user is asked to describe all the steps they take in carrying out a task.
- Videotaping – so that designers can review what users do, and see where the problems are in their designs.
- Interviews and usability questionnaires – this enables designers to evaluate what users like and dislike about the design and increase their understanding of any problems.
- Testing and data logging – where the tests require typical users to perform standardised tasks in a typical task environment so that the data can be collected on issues such as speed of task performance, type and rate of errors, subjective user satisfaction and the time taken for users to learn a specific function.
- Walk-throughs – in which a group of users step through tasks, and problems are noted for discussion.
- Focus groups – to discuss aspects of the product both before and after it is in use.
What are the principles for effective equipment design?
Any equipment interface design must connect the user’s purposes, needs, capabilities and limitations for the task’s demands. The fundamental principles of effective equipment design are shown in the table below.
Table 1. Checklist for effective equipment design
|Checklist for Effective Equipment Design|
|Visibility – are the controls positioned where the user can easily see them, with adequate lighting for doing so?||Constraints – is the equipment designed so that it limits how it can be used to reduce handling errors? (e.g. USB sticks can only be inserted in the correct way).|
|Feedback – does the system provide positive user input feedback? (e.g. such as illuminated lights on a control panel).||Conventions – does the design incorporate known conventions that work well to avoid user confusion and frustration? (e.g. the use of handles that are pulled to open objects).|
|Natural mapping – is the relationship between the controls and their effect clearly mapped? (e.g. train control signal panels are laid out to mimic the track and signal layout)||Environment – have environmental (température, noise, vibration etc) and location factors being considered for the equipment? (e.g. placing switches in positions where it won’t be easy to activate them by mistake)|
|Affordances – has the design incorporated logical shape and other intuitive characteristics of an object to suggest how it can be used? (e.g. buttons ‘afford’ pushing and pulling; knobs and switches ‘afford’ turning; ‘slots’ afford the insertion of suitable objects).||Workflow - has the pace and frequency of specific tasks being considered with the equipment? (e.g. displays and controls necessary for more frequent and more critical tasks such as emergency shutdown are readily available).|
|Workload – has the physical and mental capabilities/limitations of the users with the design interface been considered? (e.g. excess mental workload can occur with multiple alarms. Excess physical workload will occur if equipment is designed without proper regard to the way muscles and joints work).|
There are several well-established equipment control features that makes that equipment much easier to operate. While some of these items may seem obvious, it is worth remembering that long or monotonous work can cause boredom and fatigue which, in turn, lead to reduced alertness, fatigue and errors. It’s important to have a logical layout of controls and displays that assumes people will fall back on long-established habits. These desirable equipment control features are shown in the table below.
Table 2. Desirable equipment control features
|Equipment Control Feature||Description|
|Ease of Identification||Shape, texture, size, colour, location, activation method and labels all help with distinguishing between different control types. Identical labels should be placed above both the control and its corresponding display.|
|Direction of control movement||When a control is moved or turned to the right, it should mean ‘more’ or ‘on’ and its display pointer must move right over a round or horizontal display.|
|Control/Response (C/R) ratio||The relationship between the movement of a control device by the operator and the movement of the system in response, which should be fed back to the operator via a system display. Low C/R ratio control devices are ‘sensitive’ in nature, in that a very small movement of the control results in a marked change (as in the case of helicopter pilot controls). This can lead to operators ‘overshooting’ the precise location required. Conversely, high C/R ratio devices are ‘insensitive’, requiring larger operator movements.|
|Control resistance||The degree to which elastic, spring-loaded or electro-mechanical controls provide resistance.|
|Dead space||The amount of control movement around the home or neutral position that does not make the controlled system device move. In some control devices, significant amounts of dead space may affect performance adversely.|
|Location and arrangement of components||As far as possible, displays should be placed close to the controls that affect them. Components should be grouped by function and those that are important and/or frequently used should be in a prominent location. Components should be positioned to reflect commonly used sequences, and sequences should be arranged logically such as from left to right.|
Summarised from Sanders & McCormick (1993)
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