First Published April 1, Introduction PDF download for An Introduction to Human Factors Engineering by Christopher D. Wickens, Sallie, Article. (Introduction to Human Factors Engineering) - Ebook download as PDF File .pdf) , Text File .txt) or read book online. Christopher D. Wickens, John Lee, Yili D. and engineering that were presented in previous editions. The chemistry, and physics courses. In order to Ma Introduction to Human Nutrition 2nd Edition.
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An introduction to human factors engineering I Christopher D. Wickens, Sallie E. Gordon, Yili Liund ed. tvnovellas.info Includes bibliographical references and index. PDF | Whether it is the car you drive or the app on your smartphone, Designing for People: An introduction to human factors engineering. PDF | On Jan 1, , C. D. Wickens and others published An Introduction to Human Factors Engineering.
Human factors specialists usually rely on several sources of information to guide their involvement in the design process, including previous published research, data compendiums, human factors standards, and more general principles and guidelines. Data Compendiums. As the field of human factors has matured, many people have emphasized the need for sources of information to support human factors aspects of system design e. Such information is being developed in several forms. One form consists of condensed and categorized databases, with information such as tables and formulas of human capabilities. Human Factors Design Standards. Another form of information to support de- sign is engineering or human factors design standards.
He has published over peer-reviewed journal papers and 20 books on Human Factors and Ergonomics. He has also acted as an expert witness in accidents. Paul has over a decade of experience in applied Human Factors research in a number of domains, including the military, aviation, and road and rail transport and has co-authored 9 books, over 60 peer review journal articles, and numerous conference articles and book chapters.
Paul was also recently named as one of three finalists in the Scopus Australian young researcher of the year award. Laura began studying for her PhD in before moving to the University of Southampton in to take up the role of Research Fellow and continue studying part time.
Guy Walker is a Lecturer in the School of the Built Environment at Heriot-Watt University, Edinburgh, and his research focuses on human factors issues in infrastructure and transport. His research concerns human interaction with novel technology and ranges from theories of distributed cognition to social network analysis to the design and evaluation of wearable computers.
DCA offers an integrated approach to product development with services covering: applied product research and planning; design strategy; industrial design; interaction design; mechanical engineering; electronic hardware and software engineering; usability and ergonomics; prototyping and production support. Dan started his career as an automotive engineer, graduating in , with an M. Eng Hons in Mechanical Engineering and Design, receiving the 'University Prize' for the highest academic achievement in the school.
During his time in the car industry, Dan developed a great interest in ergonomics and human factors. In , Dan started his own consultancy Sociotechnic Ltd with the aim of developing industrial experience across a wide range of domains. Design and Evaluation Methods T homas Edison was a great inventor but a poor businessman. Yili Liu.
Edison thought phonographs could lead to a paperless office in which dictated letters could be recorded and the cylinders mailed to the recipients without the need for transcrip- tion. Edison pitted his taste and his technology-centered analysis on belief that the difference was not important: He lost. Second Edition. They develop technology-driven products. He is probably correct. The real use of the phonograph. Adapted from Norman.
Being first. In this chapter. Although interface design may be the most visible design element. In a book that every engineer should read. Designers tend to focus pri- marily on the technology and its features without fully considering the use of the product from the human point of view. Norman writes congently. Why do we put up with the frustrations of everyday objects. The mate- rial in this chapter provides an overview of the human factors process.
In addition to conducting basic and applied research to broaden our understanding. Human factors methods and principles are applied in all product design phases: Design and Evaluation Methods The goal of a human factors specialist is to make systems successful by en- hancing performance.
For example. It is best if the designer errs on the con- servative side in making these assumptions. The process of bringing human factors analysis in at the end of the product design phase inherently places everyone involved at odds with one another. Human factors can ultimately save companies time and money. It is not hard to understand why engineers are less than thrilled to receive the results of a human factors analysis.
Poor design is common. A human factors expert may be asked to somehow justify his or her involvement in a proj- ect and explicitly demonstrate a need for the extra expense. In most instances. In this case. But to max- imize the benefits achieved by applying human factors methods. Design and Evaluation Methods washing machines and dryers that have become too confusing to use. Mayhew provides a simple example of such an analysis. Table 1 shows a hypothet- ical example of the costs of conducting a usability study for a software proto- type.
Some types of benefits are more common for one type of manufacturer or customer than another. Even when designers attempt to consider human factors.
They have invested in the design. This expert is then placed in the unenviable position of having to come back with criticisms of a design that a person or design team has probably spent months and many thousands of dollars to develop. Mayhew gives an example for a human factors software Other quantifiable benefits are health or safety related Alexander.
Englewood Cliffs. Adapted by permission. Estimating the dollar value of averting such catastrophic failures can be quite difficult.
These numbers are multiplied by the number of times the tasks are performed and by the number of people performing the task e. The difference is then calculated. Prentice Hall. The same variables are then estimated. The estimated benefit is the total cost savings between the two.
The total benefit of the effort is determined by first estimating values for the relevant variables without human factors intervention. Principles and guidelines in software user interface design. Mayhew lists nine benefits that might be applicable and that can be estimated quantita- tively: The same values are estimated for performance if a human factors effort is conducted. It is easy to see that even small cost savings per task can add up over the course of a year.
Product design models are all relatively similar and include stages reflecting pre- design or front-end analysis activities. There are numerous systematic design models. Human Factors in the Product Design Lifecycle One major goal in human factors is to support the design of products in a cost- effective and timely fashion. Mantei and Teorey Table 2 shows the estimated benefits..
Karat reports a case where human factors was performed for development of software used by Product lifecycle models also add product implementa- tion. Marcotte et al. As noted earlier. Dix et al. Design and Evaluation Methods analysis that would be expected to decrease the throughput time for fill-in screens by three seconds per screen. Refer to Alexander Bias and Mayhew Manufacturing plants can like- wise make gains by reducing costs associated with product assembly and main- tenance e.
As we will describe in the following pages. The most effective way to involve human factors in product design is to have multidisciplinary design team members working together from the beginning. User-Centered Design All of the specific human factors methods and techniques that we will review shortly are ways to carry out the overriding methodological principle in the field of human factors: For a human factors specialist.
Team members often include personnel from marketing. Design and Evaluation Methods below. Usability engineering has been most rigorously developed for software design e. User-centered design does not mean that the user designs the product or has control of the design process. Before describing these six stages in detail. Wiklund How do we put this princi- ple into practice?
Primarily by adequately determining user needs and by involv- ing the user at all stages of the design process. For large-scale projects. Data Compendiums. This standard provides detailed requirements for areas such as controls. It is important to point out that many guidelines are just that: One form consists of condensed and categorized databases. The designer must look to more abstract principles and guidelines for this information. Existing standards do not provide so- lutions for all design problems.
Human Factors Design Standards. Department of Defense. Human Factors Principles and Guidelines. Human factors principles and guidelines cover a wide range of topics. Standards are precise rec- ommendations that relate to very specific areas or topics.
Donald Norman gives princi- ples for designing products that are easy to use Norman. Such information is being developed in several forms. Campbell et al. Both contain two types of specifications: Some guidelines pertain to the design of physical facilities e. An example is the four- volume publication by Boff and Lincoln Other guidelines focus on information systems in cars Campbell et al. Engineering Data Compendium: Human Perception and Performance..
Another form of information to support de- sign is engineering or human factors design standards. Most guidelines require careful consideration and ap- plication by designers. Boff et al. As the field of human factors has matured. Design and Evaluation Methods Sources for Design Work Human factors specialists usually rely on several sources of information to guide their involvement in the design process.
On the very general end. A persona is a hypothetical person developed through interviews and observations of real people. After identifying characteristics of the user popu- lation. This includes not only users in the traditional sense.
This usually includes characteristics such as age. It is important to create a complete description of the potential user popu- lation.
This is not an appropriate analysis if the goal is to attract. What tasks must be performed? De- signing for an elastic user may create a product that fails to satisfy any real user.
Even if user characteristics are identified. Not all of the activities are carried out in de- tail for every project. For situations where products or systems already exist. User Analysis Before any other analysis is conducted. These questions are answered by performing various analyses. What are the major functions to be performed by the system. No- tice. Personas Cooper developed the concept of personas to represent the user charac- teristics in a concrete and understandable manner.
The personas exist to define the goals that the system must support and describe the capabilities and limits of users in concrete terms.
Task analysis is one of the most important tools for understand- ing the user and can vary substantially in its level of detail.
Task Analysis.. For most applications. Depending on the nature of the system being designed. Activi- ties or basic tasks that are identified in the task analysis should be described with respect to the specific environment in which the activities are performed Wixon et al.
Separate personas may be needed to describe people with other roles in the system. The persona should be specific to the point of having a name. The functional de- scription lists the general categories of functions served by the system.
The description of the persona includes not only physical characteristics and abilities. Environment Analysis In most cases. The preliminary task analysis traditionally specifies the jobs. Once the population of potential users has been identified. The environment analysis can be performed concurrently with the user and task analysis. Function Analysis.
Functions represent general transformations of information and system state that help people achieve their goals but do not specify particular tasks. Design and Evaluation Methods are not real people. Personas enable programmers and other members of the design team to think about specific user characteristics and prevent the nat- ural tendency to assume users are like themselves.
The tasks should be specific enough to include the types of cuts. A goal is an end condition or reason for performing the tasks. How to Perform a Task Analysis Most generally. A more detailed task list would describe the subtasks involved in opening the letter. Goals do not de- pend on technology. Design and Evaluation Methods the saw. In general. As a simple example. Often it is difficult to discriminate the function list from the preliminary task list because the preliminary task list does not provide a detailed description of what the person actually does.
It is not unusual for ergonomists to spend several months performing this analysis for a product or system. A task analysis for a digital camera might first specify the different types of photos reg- ularly taken by people—group snapshots.
The analysis would result in an information base that includes user goals. The following steps describe the basic elements of a task analysis: Functions represent the general transformations needed to achieve the goal. The short list of a preliminary task analysis is often adequate at the beginning of the design process.
Both the purpose and the type of the task will influence the information gathered. Describing the hierarchical rela- tionships between functions. Define Purpose and Required Data. The first step of task analysis is to define what design considerations the task analysis is to address. Design and Evaluation Methods Kirwan and Ainsworth provide an exhaustive description of task analysis techniques. Typical reasons for performing a task analysis include defining training requirements.
A second important type of information in describing tasks is information flow. A particularly im- portant type of information collected in many task analyses is the hierarchical relationships.
In this situation. While many methods are currently being developed specifically for cognitive task analysis. For some systems. Hierarchical grouping of functions. With the camera example. In other systems. Because an increasing number of jobs have a large proportion of cog- nitive subtasks. Because a task analysis can be quite time consuming. Tasks can be physical tasks. The physical space can also have a surprisingly large effect on computer-based work.
Location of equipment can greatly influence the effectiveness of people in production-line settings. Task sequence information can be particularly useful in determining how long a set of tasks will take to complete or in estimating the number of people required to complete them. One of the best resources is Kirwan and Ainsworth A third type of information describing tasks is the task sequence.
In the camera example. Schraagen et al describe several Most im- portantly. Specific task sequence informa- tion includes the goal or intent of task. After the purpose of the task analysis is defined and relevant data identified. A Guidebook to Task Analysis. A fourth type of information describing tasks is the location and environ- mental conditions. Performed in a different order. These four categories describe tasks from a different perspective and are all required for a comprehensive task analysis.
Many methods exist to support these steps. Design and Evaluation Methods uals and their roles can identify important design considerations regarding the flow of information and resources that might otherwise go unnoticed. Other useful information can be in- cluded in these four categories. This is not always possible. One of the most useful data collection methods is to observe users using existing versions of the product or system if such systems exist Niel- son.
Collect Task Data A task analysis is conducted by interacting extensively with multiple users Dia- per. Think-Aloud Verbal Protocol.
It is often difficult for users to imagine and de- scribe how they would perform a given task or activity. Verbal protocols are usually one of three types: System users are asked to perform the activities under a variety of typical scenarios. It is important to identify different methods for accomplishing a goal rather than identifying only the one typically used by a person. Task analysis tends to be characterized by periods of data collection. In addi- tion. Many researchers and designers conduct task analyses by having users think out loud as they perform various tasks.
This yields insight into underlying goals. The following methods can be used in any combination during this itera- tive process. There are a wide range of methods currently in use. As Wixon and colleagues note. This is particularly true with primarily cognitive tasks that may gener- ate little observable activity.
Wixon et al. Observation can be performed in the field where the person normally accomplishes the task. We review only the most commonly used methods..
Observations can often be much more valuable than interviews or focus groups because what people say does not always match what they do. The verbalizations regarding task performance are termed verbal protocols. The particular data collection ap- proach depends on the information required for the analysis.
Design and Evaluation Methods cognitive task analyses methods. For analysis of a camera. What kinds of things do you do. A variation on the collection of the verbal protocol is to ask users to perform the tasks while answering questions. Graesser et al. Task Performance with Questioning. Gordon and Gill have suggested the use of question probes.
The facilitator should be neutral If the task takes place quickly or requires concentration. For this reason. Hierarchical network notation graphs works especially well because interviews can be structured with questions about the hierarchical relation- ships between functions. Unstructured interviews tend to revolve around questions or statements such as Tell me about.
Design and Evaluation Methods memory or videotape review. The disadvan- tage is that it can be disruptive. It is necessary for the analyst to ask about not only how the users go about the activities but also their preferences and strategies. Unstructured and Structured Interviews. The advantage of this method over standard verbal protocols is that it may cue users to verbalize their underlying goals or strategies more frequently.
It is common to begin with relatively short unstructured interviews with users. Concurrent protocols are sometimes difficult to obtain. Bowers and Snyder note that concurrent protocols tend to yield procedural information.? Structured interviews include types of questions or methods that make the interview process more efficient and complete Creasy.
Users can be asked to provide think-aloud verbalizations. Analysts should also note points where users fail to achieve their goals. In an unstructured interview. This functions like a structured interview with the added memory prompt of watching task performance. Users are often interviewed. Retro- spective protocols can thus be easier on the user.
Focus groups are groups of between six and ten users led by a facilitator familiar with the task and system Caplan. How do you. Some- times small groups of users are gathered for the interviewing process..
It is critical to analyze the task data to identify new design concepts that help people achieve their goals rather than to design to fit the current tasks.
The questionnaires are used to affirm the accuracy of the in- formation. Surveys and questionnaires are usually written and distributed after designers have obtained preliminary descriptions of activi- ties or basic tasks. Surveys and Questionnaires. After the hierarchical outlines are relatively complete. The only exception is the case where a new mock-up or prototype is used for analyzing user activities because they cannot be sufficiently performed on any existing system.
As Roth and Woods pointed out. Focus groups are advantageous because they are more cost effective than individual interviews less time for the analyst. Task analysis usually starts with a set of lists and then breaks the tasks down further into subtasks. Design and Evaluation Methods with respect to the outcome of the discussion. Summarize Task Data Once task-related information has been gathered. An example is shown in Table 3.
These data help designers prioritize different design functions or features. In a nuclear power plant. One way to go beyond describing existing tasks is to evaluate the underlying characteristics of the environment and the control requirements of the system Vicente.
Such a matrix typically has a row for each task. For all of these methods to collect task data. Identify a good view of an interesting subject A. Pick subject B. Change position to avoid obstacles C. Adjust angle relative to the sun Step 2. Prepare camera A. Remove lens cap B. Turn on camera C. Select proper mode for taking pictures Step 3. Take picture A. Frame picture i. Select proper mode e. Adjust camera orientation iii. Adjust zoom B. Focus C.
Press shutter button. The disadvantage of using outlines or tables is that tasks tend to have a complex hierarchical organization, and this is easiest to represent and an- alyze if the data is graphically depicted. This can be done by using either hierar- chical charts or hierarchical networks. An example of a hierarchical chart is the frequently used method known as hierarchical task analysis HTA e. This is a versatile graphical notation method that organizes tasks as sets of actions used to accomplish higher level goals.
As an illustration, consider the HTA shown in Figure 1 for conducting an accident investigation. The tasks are organized into plans, clusters of tasks that define the preferred order of tasks, and conditions that must be met to perform the tasks. Another type of hierarchical graph is the representational format known as GOMS, short for goals, operators, methods, and selection rules Card et al.
The GOMS model is mostly used to analyze tasks per- formed when using a particular software interface e. Flow Charts, Timelines, and Maps. Another graphical notation system fre- quently used for task analysis is a flow-chart format.
Flow charts capture the chronological sequence of subtasks as they are normally performed and depict the decision points for taking alternate pathways. Conduct accident investigation. Plan 0: On instruction from supervisor do 1; when all evidence is collected do 2 through 5. Collect 2. Analyze 3. Integrate facts 4. Validate 5. Make evidence facts and draw conclusions conclusions recommendations.
Plan 1: First do 1 and 2, then 3 and 4, then 5; repeat 3 and 4 if necessary. Walk the 2. Identify and 3. Identify 4. Interview 5. Review accident site preserve evidence witnesses witnesses records. Plan 1. Do 1, 2, 3; do 4 if insufficient data from 3; then do 5; repeat 3 and 4 to meet conditions of 5.
Establish 2. State purpose 3. Let witness 4. Ask open-ended 5. Ensure that what, meeting room of interview describe what questions where, when, who, happened how, why are covered. McCallister, D. Used with permission. They show the interac- tion among individuals and task equipment. Timelines are useful when the focus is the timing of tasks, and maps are useful when the focus is the physical location of activities.
All of these methods have advantages and disadvantages, and choosing the most appropriate method depends on the type of activity being analyzed. If the tasks are basically linear and usually done in a particular order, as is changing a flat tire, for example, it is appropriate to use an outline or flow chart. If there are more cognitive elements and many conditions for choosing among actions, hi- erarchical formats are more appropriate.
There is one major disadvantage to flow charts that is often not readily apparent. There is evidence that people mentally represent goals and tasks in clusters and hierarchies. The design of con- trols and displays should map onto these clusters and hierarchies. However, when describing or performing a task, the actions will appear as a linear se-.
Receive comments Collect information. Compile bibliography 8 Proofread. Driver decision Stored information e. The basic tasks of report writing begin with identifying a topic and involve several iterative steps that result in a polished product. The double square indicates how the bibliography might be compiled using specialized software. This OSD does not include the consequences of procrastination that often dramatically alter the writing process.
This makes it harder for the designer to match the interface with the mental model of the user. To develop efficient inter- faces, designers must consider the hierarchal structure and the linear sequence of tasks.
Analyze Task Data The analysis of these data can include intuitive inspection, such as examining a flow-chart diagram to identify redundant tasks. Frequently, simply inspecting graphics or summary tables cannot make sense of complex systems. More so- phisticated analysis approaches are needed.
One simple analysis is to use a spreadsheet to calculate the mean and standard deviation of individual task times or sort the tasks to identify tasks that require certain skills or that people find difficult. The spreadsheet can also be used to combine the frequency of oc- currence and duration to determine the total time devoted to particular tasks. More sophisticated approaches use computer simulations that combine task data to predict system performance under a variety of conditions Brown et al.
These quantitative techniques provide a way of going beyond the intu- itive analysis of a diagram. Network analysis. Matrix manipulations can be used to examine information flows in a network. Figure 3 shows a matrix representation of information flows between functions. Adding across the rows and down the columns identi- fies central functions. This simple calculation shows that function 2 is central in providing input to other functions and that function 3 is central in receiving input from other functions.
Workload Analysis. The product or system being designed may be complex enough to evaluate whether it is going to place excessive mental workloads on the user, either alone or in conjunction with other tasks. When this is the case, the human factors specialist performs an analysis to predict the workloads that will be placed on the user during various points of task performance.
Sometimes this can be done using the results of the task analysis if the information is suffi- ciently detailed. Simulation and Modeling. Pew and Mavor, , Elkind et al, Safety Analysis. Any time a product or system has implications for human safety, analyses should be conducted to identify potential hazards or the likeli- hood of human error. There are several standard methods for performing such analyses.
Scenario Specification. Scenarios describe a situation and a specific set of tasks that represent an important use of the system or prod- uct. Scenarios are a first step in creating the sequence of screens in software de- velopment, and they also define the tasks users might be asked to complete in usability tests.
Those associated with the specific charac- teristics of the old technology are discarded. Two types of scenarios are useful for focusing scenario specification on the design. The first is daily use scenarios, which describe the common sets of tasks that occur daily. In the camera exam- ple, this might be the sequence of activities associated with taking a picture in- doors using a flashbulb. The second is necessary use scenarios, which describe infrequent but critical sets of tasks that must be performed.
In the camera exam- ple, this might be the sequence of activities associated with taking a picture using a sepia setting to create the feel of an old photograph.
Scenarios can be thought of as the script that the personas follow in using the system Cooper, Identify User Preferences and Requirements Identifying user preferences and requirements is a logical extension of the task analysis. Human factors analysts attempt to determine key needs and preferences that correspond to the major user activities or goals already identified. As an example, for designing a camera, we might ask users via interview or questionnaire for information regarding the extent to which water resistance is important, the importance of different features, whether camera size compact- ness is more important than picture quality and so on.
It is easy to see that user preference and requirements analysis can be quite extensive. Much of this type of analysis is closely related to market analysis, and the marketing expert on the design team should be a partner in this phase. Fi- nally, if there are extensive needs or preferences for product characteristics, some attempt should be made to weight or prioritize them. This understanding must then be consolidated and used to identify initial system specifications and create initial prototypes.
As initial prototypes are developed, the designer or design team begins to charac- terize the product in more detail. The human factors specialist usually works with the designer and one or more users to support the human factors aspects of the design. Much of this work revolves around analyzing the way in which users must perform the functions that have been allocated to the human. More specifically, the human factors specialist evaluates the functions to make sure that they require physical and cognitive actions that fall within the human ca- pability limits.
In other words, can humans perform the functions safely and easily? The initial evaluation is based on the task analysis and is followed by other activities, such as heuristic design evaluation, tradeoff studies, prototyping, and usability testing.
The evaluation studies provide feedback for making modifica- tions to the design or prototype. Frequently, early prototypes for software devel- opment are created by drawing potential screens to create a paper prototype. Because paper prototypes can be redrawn with little cost, they are very effective at the beginning of the development process because they make it possible to try out many design alternatives. This redesign and evaluation continues for many iterations, sometimes as many as 10 or The questions answered during this stage of the design process include.
Do the identified features and functions match user preferences and meet user requirements? Are there any existing constraints with respect to design of the system?
What are the human factors criteria for design solutions? Which design alternatives best accommodate human limits? Providing Input for System Specifications Once information has been gathered, with respect to user characteristics, basic tasks or activities, the environment s , and user requirements, the design team writes a set of system specifications and conceptual design solutions.
These start out as relatively vague and become progressively more specific. Design solutions are often based on previous products or systems. As the design team generates alternative solutions, the human factors specialist focuses on whether the design will meet system specifications for operator performance, satisfaction, and safety, bringing to bear the expertise gained from the sources of knowledge for design work discussed earlier in the chapter.
System specifications usually include 1 the overall objectives the system supports, 2 performance requirements and features, and 3 design constraints. The challenge is to generate system specifications that select possible features and engineering performance requirements that best satisfy user objectives and goals. The objectives are global and are written in terms to avoid premature design decisions.
As an example, the objectives for a digital camera targeted at novice to intermediate photographers might include the fol- lowing partial list:. The objectives do not specify any particular product configuration and should not state specifically how the user will accomplish goals or perform tasks. These are termed per- formance requirements and features. The features state what the system will be able to do and under what conditions.
Examples for the camera design might in- clude items such as tripod mount, flash and fill-in flash for distances up to 15 feet, zoom lens, automatic focus and shutter timing capability, at least 16 MB of memory and LCD display. The performance requirements and system features provide a design space in which the design team develops various solutions.
Finally, in addition to the objectives and system features, the specifications document lists various design constraints, such as weight, speed, cost, abilities of users, and so forth. More gen- erally, design constraints include cost, manufacturing, development time, and environmental considerations.
The constraints limit possible design alternatives. Translating the user needs and goals into system specifications requires the human factors specialist to take a systems design approach, analyzing the entire. The focus should not be on the technology or the person, but on the person— technology system as a unit. The systems design approach draws upon several tools and analyses, discussed as follows.
Quality Function Deployment. What is the role of the human factors specialist as the system specifications are written? This ensures that the design specifications meet the needs of users and do not add a great number of technical features that people do not necessarily want.
This tool uses a decision matrix to relate objectives to system features, allowing designers to see the degree to which the proposed features will satisfy customer needs. The matrix also supports analysis of potential conflicts between objectives and the system features. Figure 4 shows a simplified house of quality for the digital camera design.
The rows represent the objectives. The columns represent the performance re- quirements and system features. The task analysis and user preferences identify the importance or weighting of each requirement, which is shown in the column to the right of the objectives. These weightings are often determined by asking people to assign numbers to the importance of the objectives, 9 for very impor- tant, 3 for somewhat important, and 1 for marginally important objectives.
The rating in each cell in the matrix represents how well each system feature satisfies. Weightings reflect Ratings that reflect how the importance of well each feature serves the objectives each objective Product Features F1 F2 F3 F4 F5 01 1 3 3 9 3 1 User Goals 02 3 3 3 3 3 3 and System Objectives 03 1 9 1 3 1 9 04 9 1 3 9 9 9.
Sum of weighting For this example: The importance of any feature can then be calculated by multiplying the ratings of each feature by the weighting of each objective and adding the result.
This analysis clearly separates technology-centered features from user-centered features and keeps system development focused on supporting the objectives. The features, or variables, on which the design alternatives differ are listed as rows on the left side of a matrix, and the different design alternatives are listed as columns across the top.
Example features for the camera include the tripod mount and LCD display. Each feature or variable is given a weight representing importance of the fea- ture—the result of the QFD analysis. For the features in Figure 4 this would be the total importance shown in the bottom row of the decision matrix.
Then, each design alternative is assigned a rating representing how well it addresses the feature. This rating is multiplied by the weighting of each feature and added to determine the total benefit for a design. Tradeoff Analysis.
Sometimes a design feature, such as a particular display, can be implemented in more than one way. The human factors analyst might not have data or guidelines to direct a decision between alternatives. Many times, a small-scale study is conducted to determine which design alternative results in the best performance e.
These studies are referred to as trade studies. Sometimes, the analysis can be done by the designer without actually running studies, using methods such as modeling or performance esti- mates. If multiple factors are considered, the design tradeoffs might revolve around the design with the greatest number of advantages and the smallest number of disadvantages.
The matrix would as- sess how well features, represented as rows in the matrix, are served by the differ- ent means of implementation, represented as columns. Although the decision matrix analyses can be very useful, they all share the tendency of considering a product in terms of independent features. Focusing on individual features may fail to consider global issues concerning how they in- teract as a group. People use a product, not a set of features—a product is more than the sum of its features.
Because of this, matrix analyses should be comple- mented with other approaches, such as scenario specification, so that the. Human Factors Criteria Identification. Another role for the human factors spe- cialist is adding human factors criteria to the list of system requirements. This is especially common for software usability engineering Dix et al. Human factors criteria, sometimes termed usability requirements, specify characteristics that the system should include that pertain directly to human performance and safety.
For software usability engineering, human factors requirements might in- clude items such as error recovery, or supporting user interaction pertaining to more than one task at a time.
As another example, for an ergonomic keyboard design, McAlindon specified that the new keyboard must eliminate excessive wrist deviation, elimi- nate excessive key forces, and reduce finger movement.
Functional Allocation. Many functions can be accomplished by either a person or technology, and the human factors specialist must identify an appropriate function for each. He or she then determines whether each function is to be performed by the system auto- matic , the person manual , or some combination. This process is termed functional allocation and is an important, sometimes critical, step in human fac- tors engineering Price, An example of functional allocation can be given for our camera analysis.
We may have determined from the predesign analysis that users prefer a camera that will always automatically determine the best aperture and shutter speed when the camera is held up and focused. Given that the technology exists and that there are no strong reasons against doing so, these functions would then be allocated to the camera. However, functional allocation is sometimes not so simple. There are nu- merous complex reasons for allocating functions to either machine or person.
In , Paul Fitts provided a list of those functions performed more capably by humans and those performed more capably by machines Fitts, Given this traditional view, where function is simply allocated to the most capable system component either human or machine , we might ultimately see a world where the functional allocation resembles that de- picted in Figure 5. This figure demonstrates the functional allocation strategy now known as the leftover approach. As machines have become more capable, human factors.
Cheney, New Yorker Magazine, Inc. There are other important factors, including whether the human would simply rather perform the function. Most importantly, functions should be shared between the person and the automation so that the person is left with a coherent set of tasks that he or she can under- stand and respond to when the inherent flexibility of the person is needed. Functional allocation is closely related to the question of automation.
Support Materials Development. Frequently, these materials are developed only after the system design is complete. This is unfortu- nate. The design of the support materials should begin as part of the system specifications that begin with the front-end analyses.
A large responsibility for the human factors member of the design team is to make sure that these materials are compatible with the characteristics and limitations of the human user. This information is critical and must be presented in a way that maximizes the likelihood that the user will read it, understand it, and comply with it.
The recommendations included Training: Thirty-six employees were taught basic ergonomic principles. After evaluating these facets. Other equipment. An ergonomic analysis was carried out. These recommendations go beyond interface and interaction design for individual pieces of equipment.
Design and Evaluation Methods Organization Design Some of the work performed by ergonomists concerns programmatic design and analysis that address interface.
download of step stools: The download of step stools eliminated overhead reaching that had occurred with certain tasks. An example is given by Eckbreth Equipment redesign or replacement: Some equipment. Organi- zation design concerns the training. This company had experienced a variety of employee injuries and illness among cable formers in its shops.
Changes to existing equipment: Repairs were made to a piece of equipment. For exam- ple. The team assessed injury and accident records and employee complaints. A team consisting of process engineer. This analysis would consider a wide range of fac- tors. Design and Evaluation Methods Antifatigue mats: Floor mats to reduce fatigue and cumulative trauma disor- der were downloadd. An increasing number of human factors specialists are realizing that often an entire reengineering of the organization.
Prototypes frequently have more of the look and feel of the final product but do not yet have full functionality.
In designing computer interfaces. Bailey studied the effective- This global approach to system re- design. Job rotation: Job rotation was recommended but could not be implemented because it was the only level-2 union job in the company. Mock-ups are very crude approximations of the final product. Paper proto- types of software systems are useful because screen designs can be sketched on paper. Ergonomists should design program evaluation studies carefully in order to avoid drawing conclusions that are unfounded see Cook et al.
After the recommended changes are instituted. It is clear that human factors concerns more than just the characteristics or interface of a single product or piece of equipment.
The use of prototypes during the design process has a number of advantages: Prototypes To support interface and interaction design. New technology often changes roles of the users considerably. Because the design is not a true experiment.
This example shows that a workstation or plant analysis frequently results in a wide variety of ergonomic recommendations.