Category: Phase 4

Batch manufacturing methods have been found to be the most appropriate, due to the relatively small numbers in disability sports markets.  An economic batch quantity can be calculated once the overhead and set up costs (which are fixed) are added to the unit manufacturing costs (which are variable). A break-even point is achieved when the profit per unit made can repay the fixed and variable costs.

Many assistive technology products are made in very small batch quantities, with high cost associated with delivery of the product.  Delivery costs are not shown in example chart. Normally, this may double the retail cost from the manufacturing costs shown. These costs are often unseen by the purchaser. Those involved in raising funds for charitable support groups are not always aware of reasons behind this cost. It is something a designer and manufacturer have to take time to explain to all stakeholders to ensure they know their funds are being appropriately spent.

Useful links

Torrens, GE (2011) Universal Design: empathy and affinity. In Karwowski, W, Soares, M, M, Stanton, A, N, Eds, (ed) Handbook of Human Factors and Ergonomics in Consumer Products, CRC Press, pp.233-248 Available at: (http://www.crcnetbase.com/doi/abs/10.1201/b10950-19), Accessed: [23/09/015]

An expert review is where those considered being independently qualified about a specific aspect of a product or service can provide advice. An expert in this field may include a consultant surgeon, occupational therapist, physiotherapist, bioengineer, psychologist or ergonomist. They will investigate the specification of a given product design or service. Examples of what points to consider and how to display findings may be seen in consumer survey magazines such as ‘Which’. The magazine, published by the Consumers Association, regularly reviews a range of domestic products.

Taxonomies (look-up tables) of product characteristics can be evaluated quickly with the help of expert opinions. The expert can provide a value or metric against which performance may be measured.

Expert review can be used when a quick answer to a specific question is required in order to progress a new product design development. It may also be used to double-check/validate a new design or specification. The use of experts can speed up a design process and offer an audit trial for the validation of decisions made. This can be helpful if there are safety critical decisions relating to the product or service.

Using qualified experts can be very expensive and should always be considered as only a specific part of an answer within a new product development. (Wilson et al 1995: 423)

Useful links

Cohen, L., L.Mannion, and K.Morrison 2007. Research methods in education. 6th ed. London, New York: Routledge.

Torrens, GE (2011) Universal Design: empathy and affinity. In Karwowski, W, Soares, M, M, Stanton, A, N, Eds, (ed) Handbook of Human Factors and Ergonomics in Consumer Products, CRC Press, pp.233-248 Available at: (https://dspace.lboro.ac.uk/dspace-jspui/handle/2134/15737), Accessed: [7/11/2015]

Wilson, J. R., and E. N. Corlett. 1995. Evaluation of human work: A practical ergonomics methodology. 2nd ed. London: Taylor & Francis.

Eye tracking can be used in two forms within Assistive Technology.

The first, as a control interface for people living with severe physical impairment. There are a number of manufacturers who provide a ‘plug and play’ option of this type of control interface.

The second is research tool to track the ‘jerking’ movements of the eye, called saccades. Human use this form of movement to build up a mental map of the environment. The fixation points or gaze are linked with visual perception and gestalt or gaze theory.

When used as part of a mixed methods approach, the system can provide quantitative evidence to cross-reference or triangulate with qualitative information (from interviews or participant viewer’s comments during the study).

Eye tracking provides quantified information supporting:

• Intent of the participant viewer;
• Effectiveness of usability;
• Effectiveness of control interfaces; and,
• Effectiveness of product semantics.

Modern eye tracking equipment use infrared light reflected from the cornea of the eye to monitor eye movement. Following calibration, the movement is calculated in relation to a screen or proximal task, within a narrow field of view from the eye. A common form uses screen based infrared emitters and sensors, but they can also be mounted onto a set of glasses to wear. The points given are not exact, as there is not an exact point at which the visual axis meets the retina. They can also be used in conjunction with a head tilt monitor to monitor-head-eye position.

Software can calculate and present data from a study in a number of formats:

• Animated representations of a point and pathway of saccadic movement and fixation points;
• Static representations of saccade paths;
• Heat maps, associated with the static representation of frequency of fixation points; and,
• Blind zones, where the participant viewers did not view the areas.

The main disadvantage is cost of research version of this technology; however, the control interface cost is becoming lower. This is because the traditional AT market is now augmented by gaming eye tracking control interfaces.

Useful links

Cohen, L., L.Mannion, and K.Morrison 2007. Research methods in education. 6th ed. London, New York: Routledge.

Lidwell, W., Holden, K., Butler, J., 2003. Universal principles of design: 100 ways to enhance usability, influence perception, increase appeal, make better design decisions, and teach through design, Rockport, Gloucester.

Martin, B., Hanington, B., 2012. Universal methods of design: 100 ways to research complex problems, develop innovative ideas, and design effective solutions, Rockport, Beverly.

Torrens, G., Badni, K., Hurn, K., Storer, I.J., 2015. An introduction to the development of a product Brand: an evidence-based template for use with first year undergraduate industrial designers. Engineering Design Graphics Journal, 79(2), pp. 24 -45.Available at: (https://dspace.lboro.ac.uk/dspace-jspui/handle/2134/18574), Accessed: [5/10/2015]

Wilson, J. R., and E. N. Corlett. 1995. Evaluation of human work: A practical ergonomics methodology. 2nd ed. London: Taylor & Francis.

The origins of focus group are within market research. The activity involves a small group of people opinions of whom are used to represent a larger population. The sample group are chosen because of they have a common set of characteristics, such as gender, demographics, or medical condition. Typically a focus group may be made up of six to ten people.

A moderator provides predetermined topics for discussion and acts as a facilitator or chair for the meeting. When organising a focus group some points to consider include:

• Participant recruitment
• Personality of each participant
• Participant seating (to avoid confrontational body language)
• Recording the meeting (including flip charts, video or voice recording)
• Prompts for discussion (similar to interview method)

The meeting moderator must keep the discussion focused on the topics and manage the personalities within the group in real-time to deliver the required evidence from the selected topics within the set duration of the meeting.

In the author’s experience, focus groups are both time and resource consuming; and, difficult to manage for the quality and quantity of data obtained.  Additional factors include the vulnerable nature of the users involved and the increased opportunity for bias due the involvement of carers.

Useful links

Cohen, L., L.Mannion, and K.Morrison 2007. Research methods in education. 6th ed. London, New York: Routledge.

Langford, J., McDonagh, D., 2003. Focus groups supporting effective product development. Taylor & Francis, London.

Morgan, D.L., 1997, Focus groups as qualitative research, second edition, qualitative research methods series 16, Sage, London

Wilson, J. R., and E. N. Corlett. 1995. Evaluation of human work: A practical ergonomics methodology. 2nd ed. London: Taylor & Francis.

A critical decision to be made is whether to buy-in from an original equipment manufacturer or to manufacture the parts in-house. Many mainstream products are made up for specialist made parts from a single or limited number of world suppliers (e.g. automobile wheel bearings).

These parts have many advantages over in-house manufacture. They are made to a high standard, have a ‘data’ sheet supplied that has specifications and standards to which the component has been made, and have specialist advice about their use from the manufacturer. The disadvantage is that in some cases, the standard components available require in-house made components to connect them together, increasing the cost.

Use of original equipment manufacturer (OEM) parts has a number of advantages:

• Complex functions of a new product design may be bought rather than manufactured (e.g. USB connectors, electronic subassemblies, gears boxes, electric motors, switches);
• Safety critical items can be purchased that are to a known manufacturing and performance standard (e.g. switches, sensors, hydraulic cylinders, brakes, bearings); and,
• Prototypes may be constructed cost-effectively that represent the final production version.

An important point to consider when applying this particular heuristic or strategy is that it is employed from the start of a design process. Once a product design specification (PDS) has been produced, the identification of suitable OEM parts should be the first task. Some accommodation of the specification for the OEM part may be needed within the overall design.

Useful links

Burkitt, J., G. Martin, G.H. Kay, G. E. Torrens, C. Chapman, and D. Sandbach, 1996. The development of the port-a-bidet: A portable bidet for people with minimal hand function. Medical Engineering & Physics 18, (6): 515-8.

Burkitt, J. A., G.E.Torrens, G.H. Kay, D. Sandbach and I.A. Sutherland, 1995. The development of the Autosip: A hygienic, self-operated, drinking device for people with minimal sucking ability and/or minimal arm strength. Journal of Rehabilitation Sciences. 8, (4): 115. Torrens, G.E., Marshall, R., Burkitt, J. and Kay, G., 1996. Using modularity to produce more competitive assistive technology products, Proceedings of the 13th Irish Manufacturing Committee , Limerick, Ireland, pp 797-804 Available at: (https://dspace.lboro.ac.uk/dspace-jspui/handle/2134/15775) , Accessed:[23/09/2015] 

Paired comparisons, sometimes called pairwise comparisons, is a hierarchical ranking scale assessment method or test instrument which enables design practitioners to gauge the success of their design solutions against other similar products within the target market.  The technique presents each participant with every possible pair of similar components taken from a set of design solutions and then requires them to state a preference for one item in each pair.  This measurement method or instrument was first proposed by Thurstone. [5]

Böckenholt [6] highlights three benefits of using this test method/instrument:

• It imposes minimal constraints on the judge (participant), especially when differences between items are small, and is less prone to the influence of context;
• Internal consistency checks are available that identify judges (participants) who discriminate (choose) poorly; and,
• It provides rich data about the effects of individual differences and perceived similarity relationships among items.

Böckenholt also highlights that there are drawbacks in using this method to test products.  When multiple paired comparisons are undertaken by each judge (participant) the data may contain not only variations between each participant, but also variations at each moment during the test of all the items.

Variation or variability is a common issue within quantitative (non-parametric) testing; unidirectional variability arising from a confounding variable is called bias.  Greer and Mulhern [7] define four generic causes of variability that may be found in the application of the paired comparison method/instrument:

• Sample variation
• Individual variation
• Situation variation
• Measurement variation

The structure of a paired comparison should include:

• Participant information sheet, why the survey is being done, what will happen to the information given, contact details if further questions are asked or complaints made.
• Screening protocol (to ensure correct participants are being surveyed)
• Consent form for the participant, or their advocate, to sign;
• Keep samples out of sight of the participant, unless being compared (to avoid bias);
• ‘round robin’ comparison sheet to ensure each two samples are shown in the correct order, until all samples have been compared with each other;
• Rotate the order of the samples presented to the next participant to avoid bias (Torrens and Smith, 2013);
• Ask each participant: ‘taking first impressions only..’ choose one of the two samples.
• Comments made as the participant chooses can be recorded for cross-referencing of results;

Take advice from a statistician about which non-parametric method to use to process your data (which will be transferred from surveys or inputted directly into an electronic spreadsheet;

Get a statistician to review and help you interpret the results.

The outcomes of a paired comparison can provide a priority order of samples. When combined with qualitative comments about the reasons behind their choice, the approach can provide strong evidence for the effectiveness of a particular new AT product with clinicians and healthcare professionals.

Disadvantages are that a larger sample, (a minimum of fifty participants), are needed and to ensure reliable results, a statistician is required.

Useful links

Böckenholt U. 2002. A Thurstonian analysis of preference change. Journal of Mathematical Psychology; 46, pp300–314

Creswell JW., 2009. Research design. Qualitative, quantitative, and mixed methods approaches. 3rd ed. Sage, London.

Greer B, Mulhern G. 2002. Making sense of data and statistics in psychology. Palgrave, Baskingstoke.

Siegel S, Castellan NJ. 1988. Nonparametric statistics. McGraw-Hill, London, pp 174-183.

Sinclair, M. 1999. Subjective assessment. In: J.R. Wilson & E.N. Corlett (eds). Evaluation of human work, a practical ergonomics methodology. 2nd ed. London: Taylor & Francis, pp78-83.

Thurstone, Thurstone LL. 1927. A law of comparative judgment. Psychological Review; 34, pp273–286.

Torrens G, McDonagh-Philp D, Newman A. 2001. Getting a grip, Ergonomics in Design: The quarterly of Human Factors Applications; 9, (2). pp7-13

Torrens, G.E. and Smith, N.C.S., 2013. Evaluation of an assistive technology product design using a paired comparisons method within a mixed methods approach: A case study evaluating preferences for four types of cutlery with 34 upper limb impaired participants. Disability and Rehabilitation: Assistive Technology, 8 (4), pp 340 – 347. Available at: (https://hdl.handle.net/2134/14862), Accessed: [21/01/2021]

A prototype is a product or service sample that made for the purpose of testing or validating a concept or process. A prototype can be used for a number of reasons in Assistive Technology product development:

• The end user or stakeholders can’t fully comprehend 2D sketches or perspective drawings, requiring a 3D model.
• Prototypes can be held, sat on or be placed against or near to a user or stakeholders to provide an interaction beyond visualisation.
• Prototypes can embody physical characteristics that are difficult to present as 2D illustrations, such as weight, centre of gravity, sound, vibration, smell, or movement.
• Prototypes can be used effectively to undertake participatory design or co-design with people who have visual impairment or difficulties with depth perception.
• The fidelity or refinement of a prototype is dependent on its purpose and resources available.
• Human Computer Interaction and Apps design can be prototyped using simple line drawings of computer screens or free graphics packages used alongside basic ‘hypertext mark-up language’ (HTML) webpages to replicate control interactions.

Useful links

Martin, B., Hanington, B., 2012. Universal methods of design: 100 ways to research complex problems, develop innovative ideas, and design effective solutions, Rockport, Beverly.

Lidwell, W., Holden, K., Butler, J., 2003. Universal principles of design: 100 ways to enhance usability, influence perception, increase appeal, make better design decisions, and teach through design, Rockport, Gloucester.

Torrens, GE and Black, K (2011) Equipment design in inclusive physical activity and disability sport. In Riobas, AC, Stamatakis, E, Black, K (ed) Design for Sport, Gower, pp.153-178, Available at: (https://dspace.lboro.ac.uk/dspace-jspui/handle/2134/9025), Accessed: [23/09/2015]

Torrens, GE (2011) Universal Design: empathy and affinity. In Karwowski, W, Soares, M, M, Stanton, A, N, Eds, (ed) Handbook of Human Factors and Ergonomics in Consumer Products, CRC Press, pp.233-248 Available at: (http://www.crcnetbase.com/doi/abs/10.1201/b10950-19), Accessed: [23/09/015]

Customised interfaces and rapid manufacturing (RM) are a recent addition to the options available to a product designer. Previously used for rapid prototyping, the industry has evolved to such a level that rapid manufacturing in polymers and sintered metals are already used to tailor high-end products to a customer’s preference. They can also be used to tailor garments to individuals.  Examples include:

• Switch or control interfaces
• Orthotic supports and grips.

High-end refers to the high cost and high value of the product. RM components can cost-effectively provide customised physical interfaces for more severely physically impaired individuals that link with standardised components within the product assembly. Examples include seating through to a geared drive train or a wheelchair chassis.

Useful links

Diegel, O., Nordin, A. and Motte, D., 2019. A Practical Guide to Design for Additive Manufacturing. Springer Singapore.

Value analysis is the comparison of a function or value against cost. Application within an AT-ID process may vary from comparing a particular value in the form of a product, system or service against a defined set of metrics, such as financial cost, a performance attribute or social value. It is used as a production engineering or business management heuristic to help decision-making.

A taxonomy or matrix of values against function may also be used to reduce costs within components or a service. In production engineering value analysis is used to reduce the number of parts whilst maintaining functionality. This purpose is closely aligned with standardisation and modularity (Torrens et al 1998)

The analysis may be used as a heuristic to provide a quick answer to a design decision or as a research method relating to user requirements or through expert review.

This technique is often used in product or service reviews for consumers.

Place a list of values, (components, products, systems or systems), in a row with a column of metrics or function against which the values will be measured. Define a common rating system for the individual function against which it may be used to assess each value. The rows may be discrete from each other or of a common metric, such as cost.

Useful links

Torrens, G.E., Marshall, R., Burkitt, J. and Kay, G., Using modularity to produce more competitive assistive technology products, Proceedings of the 13th Irish Manufacturing Committee , Limerick, Ireland, 1996, pp 797-804 Available at: (https://dspace.lboro.ac.uk/dspace-jspui/handle/2134/15775) , Accessed: [23/052015]

Ulrich, Karl T., and Steven D. Eppinger. 1995. Product Design and Development. New York, New York, McGraw-Hill, United States.