Research about ragged-right over justified alignment

UPDATE: My newer post “Ragged-right or justified alignment?” replaces this post, so please step right this way…

How do you argue for the preference of ragged-right over justified alignment? Searching the web, I soon came across pages which mentioned research, but it was harder to actually find it.

If you know of any other sources, whether they argue for or against ragged-right alignment, please leave a comment.

• The National Center on Educational Outcomes put out the NCEO Technical Report 37 which summarizes several arguments and references on the topic in “Table 3. Characteristics of Legible Type”, see the entry on “Justification”. Among them are:
  • Margaret Gregory’s and E. C. Poulton’s article “Even versus Uneven Right-hand Margins and the Rate of Comprehension in Reading”, Ergonomics, Volume 13, Issue 4, July 1970, pages 427-434. From the abstract: “… made no difference for good readers, but for the poorer readers the justified style resulted in a significantly worse performance.”
  • Steven Muncer, et al’s article “Right is Wrong: an examination of the effect of right justification on reading”, British Journal of Educational Technology, Volume 17, Issue 1, January 1986, pages 5-10. From the abstract: “… with reading material presented in right-justified format and in ‘ragged’ uneven line format, subjects performed significantly worse on right-justified material.”
  • David R. Thompson’s paper “Reading Print Media: The Effects of Justification and Column Rule on Memory”, paper presented at the Southwest Symposium, Southwest Education Council for Journalism and Mass Communication (Corpus Christi, TX, October 6-7, 1991). From the abstract: “… best score for recall was recorded in the flush left/jagged right.”
• The UK government agency RNIB’s “Clear print guidelines” on designing printed information that is accessible to people with sight problems: “… avoid justified text as the uneven word spacing can make reading more difficult.”
• The SEC’s “Plain English Handbook: How to create clear SEC disclosure documents” (PDF), see p. 50: “… spacing between words fluctuates from line to line, causing the eye to stop and constantly readjust.”
• … and a thoughtful blog post by Ken Adams with an argument by Ellen Lupton, curator of contemporary design at Cooper-Hewitt National Design Museum, and author of “Thinking with Type: A Critical Guide for Designers, Writers, Editors, & Students”: “… subtle word-spacing and letter-spacing algorithms are needed to make justified text look ‘good’.”