150 Understanding Rational Decision Making
curved or straight serifs added to the ends of letters (e.g., the word “APPLE” shown here in a serif
typeface) and the more block-like sans serif typefaces (e.g., the word “APPLE” shown here in a sans
serif typeface) are equally preferred by readers.^24
Serif typefaces may be easier to read in continuous text than sans serif typefaces.^25 Inother reading situations serif and sans serif typefaces are likely to be read equally quickly.^26
In a study comparing reader responses to serif and sans serif typefaces, adult readers read an
instruction manual, tax form instructions, a business letter, and a short story all typeset both
in serif and sans serif typefaces. Readers had no significant preference for sans serif versus
serif typefaces overall. However, when readers read the highly segmented prose of the manual,
much like the highly segmented bullet points of slide presentations, they preferred sans serif
typefaces. When readers read the long continuous prose of the short story, they preferred serif
typefaces.^27
One reason readers in the study preferred serif typefaces for the short story may be thatserif typefaces tend to evoke more emotion than sans serif typefaces. Readers asked to read
satirical articles from The New York Times printed in serif typeface Times New Roman found
the articles both funnier and angrier than when they read the same articles printed in sans
serif Arial.^28
No matter which typeface is chosen, consistent use of the same typeface increases readingspeed,^29 as does the use of any standard typeface with letters of uniform proportions.^30
Ten to 12 Words per Line
The number of words on each line affects the overall legibility of a page or a presentation slide. In
documents, 10 to 12 words per line is optimal.^31 For most type sizes, that amounts to about 50 to 70
characters per line. A line length of 50 to 70 characters is also easiest for the eye to scan.^32 Keeping
lines to 50 to 70 characters may mean typing two or more columns to a page. When lines of type
are shorter or longer than 50 to 70 characters, readers decrease their normal rate of reading,^33 which
for most adults is between 150 and 250 words per minute.
For internet articles displayed on computer screens, a medium line length of 55 characters perline supports faster reading than shorter lines and also produces the highest level of comprehen-
sion.^34 On presentation slides with type sizes no smaller than 24 points, bulleted lines of type will
typically contain 55 characters or fewer.
Some Space Between Lines
Reading audiences read faster when text has 1 to 4 points of leading , or space between the lines, than
when the type is set solid —when no space is inserted between the lines.^35 For a 10-point type size,
FIGURE 4.1 A Paragraph in All Caps
BOTH HEADINGS AND TEXT ARE LESS LEGIBLE WHEN TYPED IN ALL UPPER-CASE
LETTERS THAN WHEN TYPED IN BOTH UPPER AND LOWERCASE LETTERS.^17
BECAUSE THE OUTLINE OF A CAPITAL LETTER IS NOT AS DISTINCTIVE AS THE
OUTLINE OF A LOWER-CASE LETTER, READING SPEED IS OPTIMAL WHEN BOTH
UPPER-CASE AND LOWER-CASE LETTERS ARE USED AND THE USE OF ALL CAPS
IS AVOIDED.^18 WORDS AND PHRASES IN ALL CAPITAL LETTERS TAKE ABOUT 12%
LONGER TO READ.^19 HEADLINES IN ALL CAPS TAKE BETWEEN 13% AND 20% LON-
GER TO READ.^20