For print (Generally)
In his book Cashvertising, Drew Eric Whitman cites a 1986 study of fonts (printed on paper) that found only 12 percent of participants effectively comprehended a paragraph set in sans-serif type versus 67 percent who were given a version set in serif typeface ...
In a test of three different fonts, two serifs (Garamond and Times New Roman) and one sans serif (Helvetica), he found
- 66 percent were able to comprehend Garamond;
- 31.5 percent Times New Roman, and
- 12.5 percent Helvetica
(out of a total of 1,010,000 people surveyed).
On screen (Generally)
Several observations can be made regarding the examined font types. First, no significant differences in reading efficiency were detected between the font types at any size. There were, however, significant differences in reading time. Generally, Times and Arial were read faster than Courier, Schoolbook, and Georgia. Fonts at the 12-point size were read faster than fonts at the 10-point size. In addition, a font type x size interaction was found for the perception of font legibility. In general, however, Arial, Courier, and Georgia were perceived as the most legible.
For font attractiveness, Georgia was perceived as being more attractive than Arial, Courier, and Comic, while Times was perceived as more attractive than Courier. (Bernard, et al. 2002)
But it is not that simple
Dyslexia sufferers can have different requirements. Most of the recommendations come from associations for people with dyslexia and they agree in using sans-serif fonts. The British Dyslexia Association recommends
- Use Arial, Comic Sans or, as alternatives to these, Verdana, Tahoma, Century Gothic, and Trebuchet
- Most users prefer dark print on a pale background but colour preferences vary
- Avoid green and red/pink as these are difficult for colour-blind individuals.
(British Dyslexia Association, 2012).
WebAIM also has articles and resources for those with accessibility in mind
Bernard, M. et al. (2002). A Comparison of Popular Online Fonts: Which Size and Type is Best? [Online]
Available at: Wichita State University Software Usability and Research Laboratory
British Dyslexia Association. (2012). Dyslexia style guide [Online]
Available at: http://www.bdadyslexia.org.uk/common/ckeditor/filemanager/userfiles/About_Us/policies/Dyslexia_Style_Guide.pdf