Applied Ergonomics 1971, 2.4, 207-209

Writing to be understood: why use sentences? Patricia Wright

Medical Research Council, Applied Psychology Unit, Cambridge

Wri t ten in fo rmat ion does not have to be f low ing prose. Recent studies have shown tha t abandoning the prose fo rmat for al ternat ives such as logical trees and tabulated presentat ions can of ten improve comprehension. From our present knowledge, i t seems un l i ke ly that any one style wi l l be universal ly opt imal . Wri t ten in fo rmat ion is used for many d i f fe rent purposes and in a wide var iety of circumstances. This paper discusses some of the factors wh ich need to be taken into account when selecting a par t icu lar way of wr i t ing to be understood.

The difficulties of technical writing frequently stem from the nature of the material. Often the message which the writer is trying to express involves complex relationships between events with a number of alternative outcomes needing to be dealt with. For example:

"Loosen the right hand banjo screw whenever the red light comes on, unless the oil pressure gauge reads over forty pounds per square inch in which case switch o f f the auxilliary dynamo and wait for the green light before proceeding to check the ignition element held by the left hand banjo screw." It is widely agreed that such sentences are not the

easiest to understand; but what options does the technical writer have? The message is inherently complex. How can it be presented more simply?

Alternatives to prose

There are a number of alternatives for dealing with this kind of material. For example, the information could be presented as a 'logical tree' (see Fig 1).

Experimental studies have shown that the logical tree format is more easily understood, being both more accurately and more speedily used, than the alternative prose format (Wason, 1968; Jones, 1968). Other experimental

Proozdunz when red I ~ht com~ on

Is oil pnzssur¢ under ZlOlb?

I I Yes No

I I I R . I I S.itch o, d,no o I

I Is green[ light on ?= 1

I I

Fig 1 "Logical tree 'i or flowchart

Table 1. Two-dimensional table

Red light on Green light on

Oil pressure.

Under 401b Loosen R.H. banjo screw Switch off dynamo Loosen L.H. banjo

screw

Procedure when red l ight comes on

I f oi l pressure under 40 Ib loosen R.H. banjo screw

I f oi l pressure over 40 Ib 1. switch off dynamo 2. wait for green light 3. loosen L,H. banjo screw

Fig 2 List of short sentences

comparisons have been made between people's performance using logical trees and performance when using formats such as those shown in Table 1 and Fig 2 (Wright and Reid).

Table 1 is a two-dimensional table, and Fig 2 is a list of sentences all of which are syntactically simpler than the prose given in italics in the opening paragraph. These experimental comparisons showed that there was not a single optimal way of presenting the information - although the prose version always gave the poorest performance. Various aspects of the situation in which the information was being used determined which type of presentation was best.

If you think of the person using the written information as someone with a problem to which he is trying to fred the answer, then one of two conditions may obtain. Either the user knows what are the critical features of the problem (the oil pressure level, the red/green light, etc), or he is uncertain whether these or some other features are

Applied Ergonomics December 1971 207

important. Performance tests showed that when the user was in no doubt about the relevant features of the problem, then the two-dimensional table (Table 1), was more rapidly used than the alternative formats, and with no greater likelihood of errors being made. However, when there was some uncertainty in the mind of the user as to which aspects of the total problem situation were relevant or irrelevant to its solution, then the logical tree resulted in significantly fewer errors than the other formats. The error rates and correct solution times are shown in Fig 3, where it is evident that prose was always the slowest to use and tended to be most error-prone.

The logical tree would seem to be particularly appropriate for "trouble shooting" problems, where from the very nature of the task it is unlikely that the cause of the trouble is known at the outset. Even where the number of possible faults is known to the operator, the logical tree helps the man to check through each of these possibilities without there being any risk of forgetting some. In some circumstances the logical tree may also help the reader to understand the rationale underlying a series of inter-dependent events and outcomes (Lewis, Horrabin and Gane, 1967).

Remembering messages

Sometimes the kinds of complex messages already discussed are kept available for constant reference when needed. On other occasions such messages are intended as revised operating instructions which, once read, are to be remembered for future use. But is a format which can be used most easily when the information is available, also the format which can be most easily remembered?

The study of Wright and Reid suggested this was not so. When people tried to remember the table and a logical tree, it seemed as if they were attempting to visualise the information on the page. As they solved more and more problems from memory, so this visual image became increasingly blurred and distorted, and consequently

5 0 '

4C

30

L.

~ 2 0 -

I 0 -

0 2

ss p

" ~ t , S d, S S "~

S ~

T

1 I L I I 4 6 B IO 12

Median time in sees.for correct solutions

P s t

s s S

14

Fig 3 Performance when using each of the four presentation formats to solve problems (T-table; SS - list of short sentences; LT - Logical tree; P - prose). The broken line shows performance when there was no uncertain:ty about which aspects of the problem were important (see text). The solid line shows performance when some uncertainty existed.

208 Applied Ergonomics December 1971

performance deteriorated. With a list of short sentences however, performance from memory showed a slight tendency to improve with successive problems. This "list" format would seem to be easier to remember than the other versions.

S h o r t sentences

The difference in people's performance, when using the list of short sentences and when using the prose, supports the wellknown fact that it is better to use two short sentences rather than one long one. But although it is generally true that shorter sentences are more easily understood than longer sentences (Flesch, 1948), there is undoubtedly a point at which this ceases to be the case.

Consider an instruction such as "Before you release the gland nut on the aeration control check that the bundy pipe is at forty five degrees to the aluminium housing of the ignition element" This sentence is 29 words long. It can be reduced to 16 words as follows: "Checking bundy pipe forty five degrees to ignition element aluminium housing release aeration control gland nut'" Some of the changes made in this second version are probably helpful; others are not. One change that has been made which is likely to increase people's understanding is the resequencing of the clauses. As a result of this change the operation specified in the first clause is carried out before that mentioned in the second. It would probably have b e e n

a further improvement for the first clause also to be the main rather than the subordinate clause (Clark and Clark, 1968; Smith and McMahon, 1970) eg "Check bundy pipe... before releasing... ""

However, the other alterations to the first version were probably much less helpful. The reordering of terms to form compound nouns eg "ignition element aluminium housing", is far more likely to reduce comprehension than improve it. It is true that these changes have shortened the sentence, but sentence length alone is not enough to specify how difficult readers will find the material. Most "readability" formulae involve, among other things, a ratio of the number of syllables to the number of words in each sentence. The lower this ratio the easier the material is to understand. Forming compound nouns from adjectival phrases only serves to increase the syllable to word ratio. In the above two versions of the same sentence, the ratio for the first sentence is 1-6 and for the second sentence is 2.1 - this is a 30% increase in the index of difficulty.

There exists further evidence that shorter does not mean better. Experimental studies have shown that omitting relative pronouns (which, that, who) from sentences, increases the difficulty of the sentences (Hakes and Foss, 1970). Short but not telegraphic would seem to be the rule for making sentences easily understood.

Jargon

One other aspect of technical writing which sometimes impairs understanding is the use of technical terms and jargon. The need to keep specialised terms to a minimum has been stressed by Chapanis (1965) and Houghton (1968). These authors cite several examples of the way in which such terms are often unnecessarily used. What advantage is there in referring to 'circular orifices' if you mean 'round holes'?

Probably the ideal way of rninimising jargon in many kinds of instructions is to abandon the conventional prose

format. Instead, diagrams and photographs can be used to illustrate the instructions. For example Fig 4 suggests an alternative way of describing the "gland nut" adjustment previously discussed. No technical terms are needed, since the components themselves are shown. For this reason it is dearly much less likely that the operator will make a mistake in identifying components.

Choices within alternatives

From the discussion of formats such as logical trees and tables, it may have been thought that there were no variations of any significance within these formats. But this is not the case. For example Wright (1968; see also Wright and Fox, 1970) reported that two-dimensional tables, which were being used for currency conversions, were more difficult to use than other types of tablulation scheme. Consequently, since the study by Wright and Reid used these more difficult bidimensional tables, the data shown in Fig 3 may underestimate the advantages to be gained from using a tabulated format.

Similarly it is often possible to draw up a variety of logical trees for the same basic information. At the moment almost nothing is known about the factors which determine the optimal design of these types of presentation. Usually they are designed to minimise the number of choice points that a user must encounter. But in some circumstances it may be more appropriate to try to minimise the effects of errors. This might be done by arranging the choice points such that those decisions which the user was most likely to make correctly were encountered before those with higher probabilities of error.

At present we do not know whether detailed changes of parameters within the formats would greatly alter the pattern of performance shown in Fig 3. Certainly the only changes of interest would be those which gave an even greater improvement in performance as compared with prose presentation. There can be no doubt that all three of the alternatives considered by Wright and Reid (table, list of short sentences and logical tree) are much more easily understood than the 'bureaucratic' style prose which is still in common use.

Conclusion

As the title indicated, this paper has taken as its starting point the assumption that the chief aim of putting words on paper is that they should be understood by the reader. Of course this assumption is not always valid. Contracts, advertisements, catalogues, etc, are all written to meet other criteria. Again, the economics of saving space, the pressures for retaining a traditional format can weigh against the adoption of a particular style of presentation. But where the assumption is justified, where ease of comprehension is of major importance, then the writer might do well to consider whether his objective can best be served by choosing some format other than prose. The choice of format would be guided by knowledge of the circumstances in which the information is to be used. When the information is available to be read as needed:

Use tables if the reader will know what to look up. Use logical trees if the reader needs help in finding the

relevant part of the information. Use illustrations wherever possible to avoid technical

jargon.

( ~ Check this angle is 45 °

Release this nut

Fig 4 The use of illustration to eliminate technical terms.

When the information must be remembered: Use lists of simple sentences, with appropriate subheadings.

Whenever the information must be easily understood: Avoid the use of prose written in a 'bureaucratic' style.

References

Chapanis, A. 1965 Human Factors, 7, 1-17. Words, words, words. Clark, H.H. and Clark, E.V. 1968 Quarterly Journal of Experimental Psychology, 20,

129-138. Semantic distinctions and memory for complex sentences.

Fleseh, R.F. 1948 Journal of Applied Psychology, 32, 221-233. A new

readability yardstick. Hakes, D.T. and Fuss, D.J. 1970 Perception and Psychophysics, 8,413--416. Decision

processes during sentence comprehension: effects of surface structure reconsidered.

Houghton, J. 1968 'Round holes not circular orifices'. London: The

London and Southern Junior Gas Association.

Jones, S. 1968 "Design of Instruction". London: HMSO Lewis, B.N., Horabin, I.S. and Gane, C_P. 1967 "Flow charts, logical trees and algorithms for rules

and regulations". London: HMSO Smith, K.H. and McMahon, L.E. 1970 Understanding order information in sentences: some

recent work at Bell Laboratories. In Flores D'arcais, G.B. and Lewelt W.J.M. (Ed) Advances in Psycholinguistics, North Holland Publishing Co.

Wason. P. 1968 The New Law Journal, 118, 5341,548-549. The

drafting of rules. Wright, P. 1968 Ergonomics, 11,331-343. Using tabulated information. Wright, P. and Fox, K. 1970 Applied Ergonomics, 1 .4 ,234-242 . Presenting

information in tables. Wright, P. and Reid, F.

(paper submitted for publication). Written information; some altematives to prose for expressing the outcomes of complex contingencies.

OPatricia Wright 1971

Applied Ergonomics December 1971 209