Readability
Miles Tinker, for his landmark work, Legibility of Print, performed scientific studies on the legibility and readability of all-capital print. His findings were as follows:
All-capital print greatly retards speed of reading in comparison with lower-case type. Also, most readers judge all capitals to be less legible. Faster reading of the lower-case print is due to the characteristic word forms furnished by this type. This permits reading by word units, while all capitals tend to be read letter by letter. Furthermore, since all-capital printing takes at least one-third more space than lower case, more fixation pauses are required for reading the same amount of material. The use of all capitals should be dispensed with in every printing situation.
According to Tinker, “As early as 1914, Starch reported that material set in Roman lower case was read somewhat faster than similar material printed in all capitals.” Another study in 1928 showed that “all-capital text was read 11.8 per cent slower than lower case, or approximately 38 words per minute slower,” and that “nine tenths of adult readers consider lower case more legible than all capitals.”
A 1955 study by Miles Tinker showed that “all-capital text retarded speed of reading from 9.5 to 19.0 per cent for the 5 and 10 minute time limits, and 13.9 per cent for the whole 20 minute period.” Tinker concluded that, “Obviously, all-capital printing slows reading to a marked degree in comparison with Roman lower case.”
Tinker provides the following explanations for why all capital printing is more difficult to read:
Text in all capitals covers about 35 per cent more printing surface than the same material set in lower case. This would tend to increase the reading time. When this is combined with the difficulty in reading words in all-capital letters as units, the hindrance to rapid reading becomes marked. In the eye-movement study by Tinker and Patterson, the principal difference in oculomotor patterns between lower case and all capitals was the very large increase in number of fixation pauses for reading the all-capital print.
All caps text should be eliminated from most forms of composition, according to Tinker: “Considering the evidence that all-capital printing retards speed of reading to a striking degree in comparison with lower case and is not liked by readers, it would seem wise to eliminate such printing whenever rapid reading and consumer (reader) views are of importance. Examples of this would include any continuous reading material, posters, bus cards, billboards, magazine advertising copy, headings in books, business forms and records, titles of articles, books and book chapters, and newspaper headlines.”
Colin Wheildon stated that there is an "apparent consensus" that lower-case text is more legible, but that some editors continue to use all caps in text regardless. In his studies of all caps in headlines, he states that, "Editors who favor capitals claim that they give greater emphasis. Those who prefer lower case claim their preferences gives greater legibility." Wheildon, who informs us that "When a person reads a line of type, the eye recognizes letters by the shapes of their upper halves," asserts that recognizing words in all caps "becomes a task instead of a natural process." His conclusions, based on scientific testing in 1982–1990, are: "Headlines set in capital letters are significantly less legible than those set in lower case."
John Ryder, in the Case for Legibility, stated that "Printing with capital letters can be done sufficiently well to arouse interest and, with short lines, reading at a slowed speed is possible – but in principle too many factors of low legibility are involved."
Other critics are of the opinion that all caps letters in text are often "too tightly packed against each other".
Read more about this topic: Allcaps