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that sentences don't have to be of a uniform length.
They advise you to adopt the standard of average
sentence length. That is, some sentences will be very
long, some short; but on the average they should be
short.
Rudolf Flesch in THE ART OF PLAIN TALK and
Kenneth Houp and Thomas Pearsall in REPORTING
TECHNICAL INFORMATION are quite specific in
relating number of sentence words to ease of understanding. Here is Flesch's correlation of number and
difficulty:
Number of Words
Reading Ease
8 words or less
11
Very Easy
Easy
Fairly Easy
Standard
Fairly Difficult
Difficult
Very Difficult
14
17
21
25
29 words or more
To summarize Flesch's findings, he says that an average
length of 17 words makes for good readability. Houp
and Pearsall, on the other hand, suggest a 21-word
average as a good target to aim for.
Reducing sentence length doesn't mean you'll confine
your presentation to simple sentences. No, you'll still
balance and mix simple sentences with compound and
complex, though the proportion of simple sentences will
doubtless increase. What you will do, however, is reduce
the number of subordinate clauses, phrases, and other
modifiers in each sentence.
To illustrate how our documentation would shape up
against the Flesch and Houp-Pearsall measures, let's
analyze some passages chosen at random. Here are the
paragraphs; the analyses follow.
1.
"These procedures might include, but are
not limited to, relationships between transactions and data bases, and responsibilities
of the users and data base personnel. In
order to fully accomplish all the tasks
6-7