This paper presents some of the conflicting advice offered to designers on one particular topic in accessibility: the choice of font size for visually impaired people. This creates practical difficulties for designers when trying to apply the advice. It was delivered as part of the workshop, “Raising designers awarenes of accessibility issues,” at INTERACT ’99, Edinburgh.
Background to the research
I am researching best practice in forms design for the Inland Revenue Forms Unit. The Inland Revenue is actively seeking to comply with both the letter and the spirit of the Disability Discrimination Act. A key issue in forms design is meeting the needs of people with a visual impairment. I had a view that at least one factor to consider is font size, so I set out to find out as much as possible on the topic.
The obvious source was the United Kingdom’ s best known charitable organisation for blind and visually impaired people: the Royal National Institute for the Blind (RNIB). The RNIB publishes a campaigning leaflet ‘ See it Right’ and accompanying guidelines, called ‘ Clear Print’ . These guidelines have many advantages for the designer:
- They are published by a leading organisation, well known in the field and highly reputable.
- They are based on both academic research and consultation with people who have visual impairments.
- They are themselves accessible: clearly written and presented.
- The advice is straightforward and easy to understand.
However, RNIB does not represent just completely blind people, but has to consider a wide variety of visual abilities and impairments. Its guidance reflects their disparate needs:
“For the general reader type sizes between 8 point – 10 point (this means the height of a letter x is around 1mm – 1.5 mm) are frequently used. These print sizes are not legible enough for many readers, including, of course, blind and partially sighted people.
“RNIB’ s own aim is to produce documents for general readers using 12 point (to give an x height of approximately 2mm) and this is the size of print to which we believe others should also aspire. …
“RNIB’ s research has shown that a significant proportion of blind and partially signed people can read large print. RNIB recommends 14 point as the minimum print size for material intended for blind and partially sighted readers. However, RNIB sometimes uses 16 point when producing information for blind and partially sighted readers as, in our experience, many blind and partially sighted people need a typesize larger than 14 point.
It is difficult to be prescriptive in this area, as factors such as typeface and type weight will be relevant to any decision on type size. There appear to be no advantages in enlarging type above about 20 point, though larger sizes may be necessary for headings.” 
For the form designer faced with a form currently in 8.5 point, this leaves many questions unanswered. For example:
- How many people will find 9 point difficult? What about 10 point?
- How many partially sighted people are excluded by 12 point?
- Why does the RNIB not use 14 point itself, if it considers 14 point is the minimum?
- How many blind and partially sighted people need 18 point or higher?
- Why is there no advantage in increasing about 20 point?
- Why is there an advantage in a font over 20 point for headings alone? And if so, how big should the headings be?
The final sentence, and the other factors quoted in the guidelines, alerted me to the importance of considering more than simply the size of type. Also, it was apparent that simply increasing font size introduces other accessibility problems. One form I investigated was originally standard A4 size (29.7mm x 21mm). Enlarging it so that all print was at 18 point or higher meant that the form became A2 size (59.4mm x 42mm) . A form the size of a flip-chart poses insuperable problems for handling.
Different factors listed as important
Faced with the complexity of this guideline, I started to research the factors that affect legibility – apart from size. Even a short survey of some literature showed me that the only factor that is consistently listed as important is size.
- Letter spacing
- Word spacing
- Position of line split
- Width and relationship of columns
- Pictorial material
- Size of response areas in forms
- Letter shapes (e.g. closed/open ‘ a’ )
- Serifs and shape of serifs
- Standard page sizes (A4)
- Method of reproduction
Gregory alerted me to appropriateness to audience. “When designing for large print you should try to avoid making the document look as if it’s aimed at children – the “Janet and John’ design style.” 
Applicability of the research
This plethora of factors also made me wonder about whether the research on which they are based is applicable to forms. Hartley, for example, warns us to be careful in our interpretation of this research: “Taking a critical look at the validity and representativeness of the results, I think there is a good case for believing that they apply to the reading of continuous text but not necessarily to other special reading situations, such as reading signs and labels, maps and diagrams, or using “search” techniques” .
And Love had similar problems to mine: “Unfortunately, much of the research in these areas is not very helpful to designers of instructional materials. This is principally because variables such as type-size, line-length and inter-line space have not been studied in the ‘ real-life’ context of instructional text. Most researchers, for example, have considered issues of type-size in short, simple settings of continuous prose. Furthermore, they have usually used ‘ justified’ text. “
I also discovered that there is no one definition of visual impairment. Nor does the term ‘visual impairment’ tell you how much someone can read. “There are statutory or legal definitions of blindness and partial sight, but the mere statement of visual acuity – which is the basis of most attempts at defining visual handicaps – often gives a misleading idea of the a person’ s functional acuity – that is the amount of eye-sight he actually makes use of.” 
Needs of the designers
Because I had difficulty obtaining a coherent and defensible set of guidelines, I tried a different approach. I looked for models of the reading process, and tried to produce a model that the designers could relate to the choices they have to make. So far, this has not been successful. The designers want something that can be applied quickly and simply. They do not have time to explain the difference between visual and functional acuity if their font decision is challenged by a domain specialist in a meeting.
The straightforward advice in the RNIB’ s guidelines is the first step, as it gives them some immediate rules to follow. What we need next is something that will help us decide what to do when we have to make compromises in the design, for example choosing between font size and paper size.
There is not yet a conclusion, but work in progress. The traditional usability issues of users, task and environment are as important here as in any other usability issue. These issues apply both for choice of font, where we need to understand the needs of the users when considering our choices. But equally, they apply to the guidelines themselves: who will use them, for what task, and under what circumstances?
1. Shaw, A. (1970) Research into print design for the visually handicapped reader, in Print for the visually handicapped reader – conference sponsored by the Library Association and the National Association for the Education of the Partially Sighted
2. Royal National Institute for the Blind, (1996) See It Right, Clear Print Guidelines Factsheet
3. Royal National Institute for the Blind (1993) See it Right: new approaches for information for blind and partially sighted people
4. Love, G. (1987) Now you see it Now they don’t: Printed information, designers and people with eye disorders. Leicester Polytechnic
5. Hartley, J. (1994) Designing Instructional Text, Third Edition, Kogan Page Ltd, London
6. Gregory, W. (1996) The Informability Manual: Making information more accessible in the light of the Disability Discrimination Act, HMSO