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Fundamental Principles and Priority Setting
for Universal Usability

Gregg Vanderheiden, Ph.D.
Trace Research & Development Center
2107 Engineering Centers Bldg.
1550 Engineering Dr.
Madison, WI  53706 USA
+1 608 263 5788


There are a number of interrelating factors that must be considered and weighed against each other when deciding which features or capabilities should be added to a product to increase its flexibility and usability by a wider range of users.  Not all strategies or approaches are created equal, and designers have limited resources in developing and improving products.  It is, therefore, important that the different dimensions of usability be understood and that priorities be applied appropriately.  This paper attempts to delineate some of the key dimensions of usability and to begin the process of providing a rationale for prioritization between possible changes to a product’s interface.  The paper discusses a multidimensional prioritization approach that is coupled to a vector-based usability evaluation procedure currently being developed.


Universal Usability, Accessibility, Universal Design, Disability


Universal usability probably has as many definitions as there are people talking about it.  The definition used in this paper is:

A focus on designing products so that they are usable by the widest range of people operating in the widest range of situations as is commercially practical.

As one might imagine, there are no universally usable products.  There simply is too great a range of human abilities and too great a range of situations or limitations that an individual may find themselves in.  Thus, universal usability is more a function of keeping all of the people and all of the situations in mind and trying to create a product which is as flexible as commercially practical, so that it can accommodate the different users and situations.  It is important to note that universal usability does not refer to usability by people with disabilities.  Although disability is one type of limitation or variation in human performance which universal usability attempts to address, it is not the only type.  In fact, for every type of disability there are situational constraints which would provide the same requirements.  For example:


There are a number of factors that have led to the recent interest in universal usability.  The two primary driving forces have been disability access and mobile computing.  Recent laws have mandated that some products be made more accessible for people with disabilities.  Section 255 of the Telecommunication Act requires manufacturers of telecommunication products and services to make their products accessible to people with disabilities where it is "readily achievable." Section 508 of the Rehabilitation Act requires the federal government to show preference when purchasing electronic and information technologies toward those that  are accessible to people with disabilities where it is not an "undue burden," thus making accessibility commercially advantageous.

In addition to government action, the rapid increase in numbers of individuals who are older is also starting to provide a market "pull" toward more accessible products.  As can be seen from Figure 1, functional limitations increase sharply as we age.  Figure 2 shows that a large percentage of these limitations deal with vision, hearing and physical abilities, which can directly affect product usability and which can be affected by product design.

Another major force has been the rise of mobile computing, which has resulted in the need to design products that are usable in a very wide range of environments and circumstances.  It is also resulting in information systems that are being accessed  by people using a very wide range of technologies, from audio-only phones to small resolution displays to high speed, high resolution workstations. 

Functional Limitation as a Function of Age. [D]

Figure 1

Prevalence of Selected Impairments within Age Groups [D]

Figure 2


In looking at accessibility/usability features, it is important to prioritize because of the multi-dimensional nature of disability (vision, hearing, physical, cognitive) and the large number of individual design techniques or strategies which might be implemented for each dimension.  We recently analyzed a number of design strategy collections and identified between 200-300 different strategies for making products more accessible to people with disabilities (and this does not include the large number of different strategies documented in general usability literature).  Without a means to prioritize, two behaviors have been observed in our interactions with industry.

First, product designers become overwhelmed with the sheer number of different techniques and strategies.  Just contemplating building over 100 different strategies into a product causes many to walk away or to approach feature selection (focusing of their efforts) in a somewhat random fashion.  Usability tests by themselves are not a solution to the problem of being overwhelmed, since they quickly generate a long list of problems that, in turn, point back to the even longer list of potential solution strategies.

The second behavior observed is a poor prioritization in efforts where features that were first thought of or easiest to implement are chosen rather than strategies which are more important.  The result is a product which has multiple low priority features (which are helpful but not essential for access) while lacking key high priority features which are needed to make the product (or key functions of the product) accessible for the same disability group.  This is equivalent to changing the plush carpet in the entire building to a tighter nap to make it easier for wheelchairs to get around, but leaving the steps at the front door and having no elevators to get off of the ground floor.

The purpose of our efforts in this area is to map out the dimensions of complexity involved and then to develop simplified and straightforward (as possible) techniques and procedures for addressing or accommodating them.  The advice of Albert Einstein is appropriate to remember here.

Everything should be made as simple as possible. But no simpler.
- A. Einstein


In looking at the usability of a product to different people, there is a continuous range that runs all the way from:

Even the features vary in importance to the overall use of the product.  Some features are essential while others are merely convenient..

In our work, we have found it useful to adopt a three-tier system for evaluating the importance of product features, as follows.

Level 1 – features which, if they have not been implemented, will cause a product to be unusable for certain groups or situations.

Level 2 – features which, if not implemented, will make the product very difficult to use for some groups or situations.

Level 3 – features which, if they are implemented, will make the product easier to use but do not make a product usable or unusable (except for individuals who are just on a margin due to other factors and this small amount of usability pushes them over the threshold).


In addition to the accessibility/usability dimension, there is a second dimension that deals with independence versus co-dependence.  All of us depend upon others for some aspects of our lives.  A few of us know how to repair our car and television set.  Some of us don’t know how to change printer cartridges or clear paper jams or reformat our hard drives.  In our daily lives there are some things we need to be able to do independently and some things which we can depend on others for.  In setting usability priorities, this independence/co-dependence can be taken into account to facilitate decisions regarding expenditure of effort. 

For example, it is more important that an individual be able to load their work into the input hopper on a copier and operate the controls to get the required number and type of copies than it is for them to be able to change the toner or clear a paper jam.  In fact, in many offices only people trained in clearing paper jams are allowed to do so.  Loading new reams of blank paper into the copier generally falls somewhere in between.  Similarly, it is more important for an individual to be able to launch and operate programs than it is for them to be able to configure their modem settings.  This importance stems not from the technical difficulty of the two tasks but from the fact that one is an activity which is required continuously as a part of their daily operation, whereas, the other is something which needs to only be done once or which can be planned for and scheduled when there is someone to assist. 

Figure 3 shows a rough hierarchy based on the need for independence versus the ability to deal with co-dependence.  The exact ordering of the items will vary for different types of products and different environments (e.g., the availability of the co-dependent facilitator), but the general ordering can be seen.  This can then be used to set priorities in a resource-constrained or time-constrained product design program. 

  1. Functions/features needed for basic use of the product
  2. Unpredictable, but typically user-serviceable (by "average" user)   maintenance or recovery operations
  3. Unpredictable service, maintenance or recovery, typically corrected by support personnel
  4. Predictable or schedulable  maintenance that can be delegated to others
  5. Unpacking and initial setup
  6. Repair

NOTE:  The location and availability of support personnel (e.g. in a home office) affect this dimension.

Figure 3  Priority based on the need for person to be able to independently accomplish tasks


A third dimension to prioritization deals with the need for efficiency.  If a task is performed only once a day and there is no particular time constraint on its accomplishment (e.g., the person isn’t trying to disarm an alarm before it goes off), then the relative efficiency of operation is not as critical as a function which must be used continuously throughout the day.  For example, if it takes an individual five times longer to operate the “on” switch on their computer than the average worker, it will not have a major impact on their productivity or effectiveness.  In fact, turning the on switch is such a small part of booting a computer that the total time it takes for them to turn the computer on is likely to be only negligibly longer than the time for any one else to boot their computer.  If it takes an individual five times as long to type characters on their computer, however, and they spend the bulk of their day entering information into their computer, the difference in efficiency could be catastrophic.  If it took them five days to get an average day's worth of work done, it would be hard for them to compete in either an educational or work environment.  Thus, for the on/off switch, level 1 accessibility may be all that is required.  However, for data entry level 1, 2, and 3 may all be critical on an individual’s workstation.

A close parallel to efficiency is the urgency issue.  If there are situations where a user must do something within a particular time constraint in order to avoid an adverse situation then, even if it is rarely done, it may be important to strive for level 2 or level 3 usability in order to allow the individual to be able to carry out the activity within the time allowed. 

The importance that is attached to this dimension is the function of at least three factors.

  1. The reversibility of the action.
  2. The severity of the consequence for failure.
  3. The ability of the person to adjust the time span to meet their increased reaction times.

Situations where the result is not reversible or is dire in nature and is also of a type that does not allow for user adjustment or extension (as in some security related situations), would create the highest priority for providing not only an accessible but a highly usable interface for the group or situation. 


In setting priorities for implementation of usability features in products, a factor that is often used to select features is the ease with which they can be implemented in the product.  In this context, “ease” may have many different characteristics, including cost in dollars, cost in time, ease in getting clearance from supervisors, minimized impact on other features, minimized impact on testing, minimal impact on documentation, etc.  Often referred to as “low hanging fruit,” such features are often very tempting when compared to features which are much more difficult to implement.  Although it is always good to look at this dimension, there is great danger here as well.  Often this strategy leads one to believe that five low hanging fruit features must be better than one that is more difficult to achieve.  This can lead to the implementation of multiple Level 3 features instead of key Level 1 features.  Often this occurs with features intended to benefit the same disability group so that a product may have usability features for a disability group that cannot, in fact, use the product.

Within Level 1 accessibility features, however, one will also often find either a low hanging fruit or features which would have such mass-market appeal that their “costs” are offset by their market benefit.


A number of different schemes have tried to capture the different dimensions of universal usability for different product types.  The Telecommunication Access Advisory Committee, Access Board, and FCC came up with 23 guidelines.  The Electronic and Information Technology Access Advisory Committee came up with over 90.  The Access Board in its Section 508 proposed rulemaking reduced these to just under 70.

In each of these cases the guidelines are a combination of general performance-based guidelines and specific design-based guidelines.

In order to provide a more generic approach, we have been experimenting with a collapsing of the guidelines into their essential components.  This collapsing takes the form of identifying the key objectives or requirements for providing more flexible universally usable interfaces and then identifying key strategies for meeting these objectives.

The current working draft is provided in Figure 4.

This approach breaks the requirements into five major objectives.

  1. Ensuring that all information presented by or through the device can be perceived (even if all sensory channels are not available to the individual). 
  2. Ensuring that the device is operableby the user (even if they are operating under constraints).
  3. Facilitating the abilityof the individual to navigate through the information and controls (even if they are operating with constraints).
  4. Facilitatingtheir ability to understand the content.

If it is not possible to achieve the above four objectives directly, then the goal is to make the product compatible with the common tools that users may have with them in order to maximally achieve the above four objectives.

From the wording of the four objectives it can be seen that the first two tend to be Level 1-like objectives, in that they are talking about providing the basic ability to perceive and operate.  Objectives 2 and 3 are more Level 2 / Level 3 oriented in that they facilitate.  (Compatibility overlaps all four of the above).

Despite the Level 1 / Level 2 appearance of the four basic objectives, elements of Level 1, 2, and 3 usability can be seen in all four objectives. 


In looking at the dimensions it is important to note that the cognitive dimension is unique from the other dimensions, whereas, it is possible to make most products usable to individuals with no vision or no hearing and even with essentially no physical ability.  There are very few products, if any, that are usable by individuals with no cognitive abilities.  This is due to the fact that it is possible to translate most types of information between sensory modalities and most types of activities between physical interface techniques, but we do not have any mechanism for transferring cognitive processing into another domain.  While it is true that there are some activities and some types of information that we do not have good strategies for providing access to by individuals with severe or total visual limitation, severe or total hearing limitations, or severe or total physical limitations, the number of devices and activities that are excluded are much smaller than for severe or total cognitive limitations.  For this reason, strategies for “enabling access” for people with cognitive disabilities basically look like techniques to “facilitate” with each technique which “facilitates” pushing a few more people over the threshold into the category of individuals who “can use” a product.

It is also important to note that there are a number of dimensions which are often lumped in with cognitive disabilities, where products can be made accessible.  For example, there are strategies which can allow individuals who are completely unable to read to be able to effectively use a very wide variety of products.  In this case, the difficulty is not in general cognitive processing or memory but rather in a specific skill, which is reading.


Matched with each of the basic objectives is a list of generic strategies for addressing the objective.  These are shown along side the basic access principles in Figure 4. 

Each of these generic strategies would take a different form in different technology families.  In some cases, such as the area of web technologies, some of the strategies would be implemented on the web content pages while others would be implemented in the user agents or browsers.  The goal of Figure 4 and the access principle and strategy consolidation effort that it represents is to try to boil the overall universe of requirements and strategies down to their essence so that

it is easier to get one’s mind around the whole set.  In doing

so, a certain amount of simplification is necessary.  As a result, a condensed set of requirements and strategies such as this needs to be elaborated within each of the different technology families with which it is intended to be applied.  We are currently in the process of continuing to flesh out and make complete this simplified view (or simplified views like this), as well as to provide details on how these might be elaborated and applied within various technology areas. 

To track our continuing work in this area, the reader is referred to our website at


I would like to acknowledge the assistance of Kitch Barnicle Ph.D. in reviewing and commenting on this paper during its preparation.

This is a publication of the Trace Research & Development Center which is funded, in part, by the National Institute on Disability and Rehabilitation Research of the Department of Education under grant numbers H133E980008, H133E990006 and H133A60030.  The opinions contained in this publication are those of the grantee and do not necessarily reflect those of the Department of Education.


1. Bureau of the Census, Series P-70, #8.  Survey:  SIPP, 1984.

2. LaPlante, M.P.  Data on disability from the National Health Interview Survey, 1983-85: An InfoUse Report. Washington, DC: National Institute on Disability and Rehabilitation Research, US Department of Education, 1988.

[NOTE: work is continuing on this topic in connection with Section 508 implementation teams.  The presentation of this paper will reflect the latest developments.]

Linear version of access table

Basic Access Principle Why How –General

Make all information perceivable  (including key & control -status & labels)

  • Without vision
  • Without hearing
  • Without reading (low vision or cognition)
  • Without color perception
  • Without causing seizure

Information which is presented in a form that is only perceivable with a single sense (e.g., only vision or only hearing) is not accessible to people without that sense.  [Also not accessible by anyone using a mobile technology that does not present all modalities such as a phone – or automobile audio-only browser.]

Make all information available either in a) presentation independent form (e.g., electronic text) which can be presented in any sensory form, 


b) sensory parallel form  where forms suitable for presentation in different sensory modalities are all provided  in synchronized form (e.g., a captioned and described movie),


Provide a mechanism for presenting information in visual, enlarged visual, auditory, enhanced auditory (louder and if possible better signal to noise ratio) and, where possible, tactile form.


- To meet these requirements, text formatting must be electronically readable and presentable without vision.

Provide as least one mode for all product features that is operable:

  • Without pointing
  • Without vision
  • Without requirement to respond quickly
  • Without fine motor movement
  • Without simultaneous action
  • Without speech
  • Without requiring presence or use of biological parts (touch, fingerprint, iris, etc.)

Interfaces which are technology or technique specific cannot be operated by individuals who cannot use that technique (e.g., a person who is blind cannot point to a point in an image map; some people cannot use pointers accurately).  [Also not accessible to mobile users who are using voice to navigate for example]

a)  Make all interfaces controllable via ASCII/UNICODE input and output,  AND

b) Have all text output voiced or compatible with device that will voice it,  AND

c) Make all input and displayed information non-timed, or allow user to freeze timer or set it to very long time ( 5 –10  seconds to do single action,   2-4 seconds  to stop action),  AND

d) Have at least one mode for achieving each and every function of the product that meets the following conditions:

  • No simultaneous activations
  • No twisting motions
  • No fine motor control required
  • No biological contact required
  • No user speech required;   AND

e) If biological techniques are used for security,  have at least two alternatives and preferably a non-biological alternative unless required.

Facilitate Navigation

  • Without sight
  • Without pointing ability
  • Without find motor contro
  • Without prior understanding of the content
  • Without the ability to hear

Many individuals will not be able to use alternate access techniques if their layout is too difficult to understand.

Many individuals will not be able to operate products, such as workstations, with sufficient efficiency to be competitive if navigation is not easy. 

a) Make overall organization understandable (e.g. provide overview, table of contents, site maps, etc.).

b) Don’t mislead/confuse.  (Be consistent in use of icons or metaphors. Don’t ignore or misuse conventions.)

c) Allow users to jump over blocks of undesired information (e.g., repetitive info) , especially if browsing auditorially.

Facilitate Understanding of Content

  • Without skill in language used on product
  • Without good memory
  • Without background

People with cognitive difficulties may not be able to access and use complex devices or products with language.

Many others may find that they are unable to master alternate access techniques if layered on top of complex interfaces or content.

a) Use the simplest, easiest to understand language as is appropriate for the material/site/situation.

b) If unexpected languages are used – be sure the language used is identified to allow translation.

Compatible with Assistive Technologies commonly used by people

  • With low vision
  • Without vision
  • Who are hard of hearing
  • Who are deaf
  • Without physical reach and manipulation
  • Who have cognitive or language disabilities

In many cases, a person coming to a task includes the assistive technologies they have with them.  If they cannot use products directly, it is important that the products be designed to allow them to use the tools they carry with them to access and use the products.   This also applies to mobile users, people with glasses, gloves or other extensions to themselves.

a) Support standard points for connection of

  • audio amplification devices
  • alternate input and output devices (or software)

b) Do not interfere with use of assistive technologies

  • hearing aids
  • system based technologies

Webmaster's note: An updated version of the information in the above table can be found on the Basic Principles and Strategies for Access to Electronic Products and Documents page.