Re: IDENTIFIERS in Upper Case

[mheaney@ni.net (Matthew Heaney)]

In Guidelines for Enterprise-Wide GUI Design, authors Susan Weinschenk and
Sarah C. Yeo state that "Sentances in all capital letters are 20 percent
more difficult to read than sentences with upper- and lower-case letters. 
Avoid using all caps for large blocks of text." [p. 101]  They later state,
when discussing online help, that one should "Never use all caps, except
for acronyms and initializations.  Words in all caps are harder to read."
[p. 144]

In Usability Engineering, author Jakob Nielsen states that "On alphanumeric
terminals, UPPERCASE TEXT CASE CAN ALSO BE USED TO GET THE USERS'
ATTENTION, but upper case should be used sparingly as it is about 10%
slower to read than mixed-case text." [p. 118-9]

In Principles and Guidelines in Software User Interface Design, author
Deborah J. Mayhew states "Avoid heavy use of all-uppercase letters.  Text
in all uppercase is more difficult to read than text in mixed case.  Tullis
(1988) reviews literature suggesting that people read mixed case text about
13% faster than uppercase.  This is because lowercase letters look more
different from one another than do uppercase letters, making it easier to
determine a word in part by its overall shape." [p. 469]

The Tullis reference is

Screen Design
Thomas S. Tullis
Handbook of Human-Computer Interaction
Martin Helander, ed (Amsterdam: North-Holland, 1988), p. 377-411

Jakob Nielsen writes a regular Interface column for IEEE Software.  He can
be reached at <mailto:jakob.nielsen@sun.com>.

Hope that helps,
Matt

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Matthew Heaney
Software Development Consultant
<mailto:matthew_heaney@acm.org>
(818) 985-1271