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The Development of Questionnaire Surveys for theInvestigation of Passenger ComfortBy D. J. OBOKNB a & M. J. CLARKE aa Department of Mechanical Engineering , University College of Swansea , Swansea, WalesPublished online: 24 Oct 2007.

To cite this article: By D. J. OBOKNB & M. J. CLARKE (1973) The Development of Questionnaire Surveys for the Investigationof Passenger Comfort, Ergonomics, 16:6, 855-869, DOI: 10.1080/00140137308924577

To link to this article: http://dx.doi.org/10.1080/00140137308924577

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ERGONOMICS, 1973, VOL. Hi, No.6, 855-869

The Development of Questionnaire Surveys for theInvestigation of Passenger Comfort

By D. J. OBORNE and M. J. CLARKE

Department of Mechanical Engineering,University College of Swansea, Swansea, 'Vales

In the course of this paper the authors have sought to establish the usefulness of thequestionnaire as a tool for obtaining information concerning passenger comfort fromtho passengers themselves. An appropriate questionnaire, developed a,t Swansea,has been used as an illustration. Whereas many pitfalls may exist in the interpreta­tion of the data, it is argued that with careful consideration both of tho questionnaireconstruction and the analysis. useful information may be obtained. Such informa­tion may be used as an indicator for further research and as a valid pointer to thesubjective feelings of tho passenger.

1. IntroductionThe problems facing contemporary transport operators have increased

considerably from those with which their predecessors had to contend. Inpast years, the important questions which faced such men were primarilythose of the safety, maintenance and viability of their transport systems. Pro­viding their vehicles travelled from A to B quickly, safely and economically,they remained satisfied. Little concern was given to the comfort requirementsof the passenger. In the highly competitive business of modern-day passengertransportation, however, it has become apparent that a consideration of theneeds of the user are paramount to the economic survival of the transportsystem itself. For this reason, present day transport operators are becomingmore and more passenger orientated in their outlook. Thus it has become asessential to discover the standards of ' comfort' required by the passenger,as it is to ensure that his journey is both safe and fast. Accordingly, thesituation has become one in which the passenger is being consulted in orderto be able to furnish transport designers with the required information.

The term' comfort' implies that some state of ' well-being' exists withina person, and it is this' state of mind' which is under investigation. Such asubjective condition may be generated by the combined effect of the manyphysical and psychological factors acting upon a person, as well as the physio­logical condition of the man himself.

Whereas the physical factors present in a transport environment fall intofairly. well-defined groups, the psychological and physiological variables of theindividual are far more numerous and less definite. These may range from thepassenger's attitude towards the particular form of transport to his state ofhealth at the time. Due also to the many interactions that occur betweensuch variables, it is clear that such factors are more difficult to elicit andmeasure than are the physical factors. It is for this reason that most previousresearch workers in the field of passenger comfort have undertaken the task ofdiscovering how the physical parameters present in a transport environmentaffect passenger comfort. The usual areas to be investigated are thoseconcerning the noise, vibrational, thermal and postural factors. In the main,however, such inquiries have been carried out in the laboratory, which is an

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856 D. J. Oborne and J1!I. J. Clarke

environment entirely divorced from the transport situation. It is rare to readof experiments carried out in the' field' in which those who use the transport(the passengers) are employed as subjects. An obvious excuse for this state ofaffairs is, of course, that the stimuli in field investigations cannot be as easilycontrolled as in the laboratory, nor may the subjects be as easily manipulated.Such arguments, however, do not excuse the present lack of reported datafrom the field, for such problems may be overcome with the use of appropriateexperimental techniques (e.g, Branton J 972, Branton and Grayson 1967).

It was with the aim of obtaining useful information from the transport usersthat a programme of research was instigated at Swansea which provided forquestionnaire surveys to be carried out on different types of transport systoms.The surveys were originally intended to investigate two related fields:(0,) obtaining subjective estimates of the intensity and comfort reducingproperties of the vehicular motion present in the vehicle, and (b) the develop­ment and design of suitable questionnaires to elicit such information. As thesurveys progressed it became increasingly apparent that passengers find greatdifficulty in extracting and considering just one physical parameter (in thiscase vehicular motion) from all the others, and the utility of any informationthat is obtained from the passenger is diminished without additional informa­tion concerning the respondents psychological state at the time. (By thislatter contention, it is suggested that the strength and direction of the passengersattitude to the journey is required, rather than a knowledge of his particularpersonality type). As a result of these two conclusions, the questionnairewas enlargcd both in design and aims to include a consideration of the physicaland psychological factors thought to be important in the determination ofpassenger comfort. Such an enlargement of the questionnaire, however,embodies related problems of analysis and interpretation and these will bediscussed later. It also follows from the above discussion that the surveyswere not merely' one-off' pieces of unrelated work but WHe, in fact, of an, on-going' design in which the findings and failures of one were used tosupplement and alter the design and operation of the next.

2. The Function of Questionnaire SurveysThe usefulfunctions of any questionnaire survey of this type may be divided

into th~ee main (but related) sections-each one of which might be a reasonfor the instigation of such a survey. These three broad functional classifica­tions (which have provided the basis for the surveys carried out at Swansea)could be said to be

to provide indications for future areas of research;to attempt to discover which factors influence a state of comfort, andhow they do so; andto obtain subjective estimates of the intensity, quality and comfortinducing or reducing properties of the factors present in a transportenvironment-from the transport users themselves.

A fourth function which is closely linked to each of the previous three, is thedevelopment of questions which are able to be understood by all members ofthe travelling public (i.e. all social classes, all age groups, etc.), and which wouldprovide repeatable information. Some of these questions will, of necessity,

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Comfort Survey 857

be of a technical nature and the unambiguous wording of such questions is anobvious requisite.

If it is required that broad indications for future areas of research should begained from a questionnaire survey, then an advantage in the design of thequestionnaire is for the questions to be as open-ended as possible. In this waythe respondents are able to give their answers without the constraints encoun­tered with more structured questions. As a result, valuable information isobtained which may then be incorporated in future, more controlled, questions.A major drawback of such open-endedness, however, lies in the lack of controlable to be exorcised over the nature of the response given. Such a problemmay be illustrated with reference to past questions which have asked passengersto describe the noise and vibration which they were experiencing. It washoped to obtain descriptors of a ' one-word' type from these questions, forexample, ' bumpy', 'rattling', but no matter how the question was phrased,and even when one word was specifically asked for, the proportion of one wordresponses to those of phrases and sentences remained low.

A second function of such questionnaire surveys, and one which stemsdirectly from the first, is the attempt to discover which variables-physical,psychological or physiological-affect a passenger's feeling of comfort. Further,it is to discover the manner in which these factors interact. This is an area ofresearch from which most interesting and useful information may be gained,but it is also an area which is complicated by the many different variableswhich influence comfort. Branton (1972), for example, has shown in a surveysampling over 1000 train users that, apart from a wish for less noise and vibra­tion, consideration was also given to the need for coat hooks, rubbish bins, andimproved toilets. Similar requests (and by implication, influences of comfort)have also become apparent from the questionnaire surveys carried out atSwansea (see Figure T). Passengers using the cross-channel hovercraft at

ts

6 OJ. of all comments

nobility to see out due to sprayo cramped .Motion levels too highsets. disc omforthcrafttemperature or ventilat ion

n proceedure

II Seats to

I Vibration'I Speed of craft off

I Noi se level too higI General untidyness ofI Comments concerning

INeed for better embarkatioIHelpfulness of slaffI Poor timetable arrangemen

I Poor drinks service

~,: 'm," 0' petr-olUntidyness of toiletsNot enough non-smoking areas

Not enough sick be gsDislike of piped music before lake-off

1~eed for more emergency exitsNeed for more hand rails

2 4 9 ~ 10 12 14 16 1;

5 10 15 20 25 30 35 40 45 50 Number of comments

Ftgure 1. The relative importance of various factors which influenced passenger comfort duringtho second Dover hovercraft survey.

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858 D. J. Oborne and M. J. Clarke

Dover were asked to comment on any aspect of the journey, hovercraft orquestionnaire that they wished, and the last page of the questionnaire was leftblank for this purpose. Because many passengers commented on severaldifferent aspects of the journey in the same answer, Figure 1 indicates not thenumber of passengers who responded, but the number of different commentsthat were made.

The third practical application of questionnaire surveys lies in obtainingsubjective estimates of the factors that influence comfort. It is within thisarea that published information is most lacking-both in terms of how passen­gers react to existing levels of noise, vibration etc., and in terms of how suchinformation is obtained.

3. The Questionnaire Developed at SwanseaThere is, at present, little information available to transport engineers

concerning desirable levels of vehicular motion. For this reason, therefore,a principal consideration in the development of the Swansea questionnairehas been the investigation of means by which reliable estimates of vibrationalintensity may be obtained from passengers in the 'field'. A further con­sideration in the design has been an attempt to discover under what conditionsan otherwise comfortable journey becomes uncomfortable. It is hoped that theinformation gained from such surveys, which have encompassed many differentforms of transport, will eventually be of use in the design of new (and perhapsmore comfortable) vehicles.

The questionnaire at present in use has been developed over the course offour main field surveys, but the preliminary interview work and developmentwas carried out using different forms of transport which were readily available,for example a mini-bus, a Land-Rover, anda trawler. Of the surveys completedto date, three were undertaken on Seaspeed hovercraft services-one fromSouthampton and two from Dover-and another sampled passengers on theBEA helicopter service at Penzance. Initially, these vehicles were chosenbecause of the predominantly high levels of noise and vibration in their environ­ment, so ensuring that the questions asked were immediately meaningful to thepassengers. A fifth survey has recently been completed on British Rail trainsbetween Newport and Reading. During a period of 2i weeks over 1500questionnaires were distributed but the analysis, as yet, is incomplete.

3.1. The Development of the Questionnaire Format

The design of a questionnaire format is always highly dependent upon theway in which the questions are to' be presented to the respondent. In the, face to face' interviewer-interviewee situation, for example, close attentionto the layout of the questionnaire is of little importance provided the questionsthemselves are well-designed. In a transport situation, however, in whichupwards of 1000 passengers may be questioned in a single survey, such anapproach is inappropriate.· For this reason, self-administered questionnairesare more useful. By this method, the questionnaires are presented to thepassengers who are then left alone for about half an hour to complete them.The completed questionnaires are then collected sometime towards the endof the journey.

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Comfort Survey 859

When presented in this manner, the questionnaire effectively takes over therole of the interviewer and so, for this reason, in addition to the necessity ofhaving well-worded questions, two further requirements need to be fulfilled.Firstly, the questionnaire should be laid out in such a way as to ensure that thequestions are not only understandable but readable. Further, the absence ofthe interviewer requires that the rapport normally established between inter­viewer and interviewee is maintained by the manner in which the questionsare worded and arranged. Such rapport should also be created by explainingto the passenger, via the questionnaire, the reasons for the survey and by givinghim assurances of complete anonymity.

The format of the questionnaire used at Swansea has changed considerablyover the period of research-s-the alterations being made in order to make thequestionnaire easier to read and complete (see Figures 2a, 2b and 2c). Forthe reasons outlined above each questionnaire has been accompanied by anintroductory letter which, as well as introducing both the research and question­naire to the passenger, provided him with instructions aimed at helping in thecompletion of some of the questions. In addition, the anonymity of the respon­dent has always been assured by enclosing each questionnaire in an envelopeand by pointing out to him that no names or addresses are required.

The first survey in which questionnaires were distributed made use of theHovercraft service between Southampton and Cowes in December] 969. Thequestions were printed on both sides of small cards which were stapled togetherto form a booklet. The first page was used to provide a brief introduction tothe research (see Figure 2a). Card was chosen in order to provide some degreeof su pport for the passenger who had to write his responses whilst in a vibratingenvironment. A similar questionnaire format was used during the secondsurvey (first Dover hovercraft survey) in April 1970, when nearly 500 question­naires were distributed over a period of four days.

After the second survey, it was decided that the size and arrangement of thequestionnaire itself required that the questions be printed in too crampeda fashion for easy reading-particularly in a vibrating environment. It was

·SUSCEl'rIBILIn OF P.lSSEIlGllIlS TO TliB 1lD'rl01l OP

FUBLIC TRANSPORT VllIlICLBS·

M part of the above Research Project, the l'ollmr1nt carda

contain a aeries of questions related to pBss8l1sera reaction to

tbe Bua as a torm or public ta-e napcr-t , Pl88.a8 will you work:

through them e t your own pace and. ring the &.ppropriate ansiler

to each qU~8t1on. On some of the questions, you will be asked

to ;>ronde a "rating". All this aeeas , is that you should

Assign a number, or mark a point aD a line, equivalent to your

judgement. For oxampl~J on ~ scale froa 0-10, a rating ot 5

'M)uld be a moderate judg6l1lent, and ~ a high judgement etc.

If ./ou rl sh to provide 6f1y t"Urther informa tiQn which you

consider relevant, will you contact Qur intarviewer at some

Figure 2a. Page 1 of the first questionnaire format (Southampton hovercraft, December 1969).

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860 D. J. Oborne and u. J. Clarke

also decided that the need for card was not as great as originally thought.Accordingly, therefore, the questions asked in the third survey (Penzancehelicopter survey) were printed (one side only) on 'A5 ' (15 x 2l cm) size paper,and the pages were again stapled together to form a booklet (see Figure 2b).A longer, more detailed introductory letter was included as a separate sheet.

Despite such enlargcment and clarification of the questionnaire, however,it scemed on analysis of the responses from the helicopter survey that a fairnumber of passengers continued to confuse (and thus answer incorrectly) manyof thc questions. This problem was considerably lessened in the later surveysby dividing off each question, so separating it distinctly from the precedingono, The questionnaire was also altered by arranging it in a vertical orienta­tion (i.e. tho long edge of the questionnaire was vertical), giving an impression(it seems from comments received) of a more' professional '. design (see Figure2c).

3. Apart from this trip, how often have you flown In a Heltcopter ?

NEVER 1 ONCE/TWICE BEFOREI FEW TIMES A MONTH\ EVERY WEEK I MOST DAYS

4. What are your reasons for choosing this Hellcopter Service as your mode oftransport?

(Please tick those which a.To applicable, and ring the most important one).

I.

b) Novelty of the Helicopter travel.

d) Eff1clency of the aervtce ,

NO

OccupationSex

YES

Aqe

a) Short travel time.

c) Df s ltke rreve ntnc by sea,

e) Any other reasons (please specify):

5. How do you occupy most of your time during the f1tght?

READ, WORK, TALK, SLEEP, SIT AND LOOK OUT or THE WINDOW.

2. Have you ever travelled by air before?

1. Pteaae could you supply the [ollowing rntcrmettom

Figure 2b. Pago 1 of the Pcnzuncc.... hclicopter survey quest.ionnn.iro (August lHiO).

3.2. The Type of Questions Asked

Due to the function of the research being undertaken the questionshave generally been directed towards obtaining subjective estimatcs ofthe intensity of the vibration and noise present in the transport environment.For this reason, two main types of questions have been presented to the passen­ger. In the first case, he has been asked to describe the noise and vibration,whilst in the second he was usually asked to provide some sort of mting toshow the extent to which these features were present.. .

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Comfort S1Lrvey

1. At which station did you board this train?

................. . .....

2. Are you occupying a window seat?

SUI

Yes 0 No 03. Are you in a smoking compartment?

Yes 04. Would you mind supplying the following information:

Your age Sex Occupation

S. ~oughly how many ~INGLE journeys have you made by trainIn the past fortnight? (NB. A return journey wouldconstitute ~ single journeys).

Nil 1-) 4-6 7-9 10-12 13-15

OOOOCO16-18 19+

DO6. What is your main reason for making this journey by train

rather than by any other means of transport?

PLEASE TICK ONE REASON ONLY.

a) Eif i c i ency Cb) Comfort CJc) Only means of transport available CJd) Economy c::::::::Je) Speed 0f) Any other reasons?

- 1 -

Figure 2c. The first page of t.hc latest. questionnaire format (B.B-. t.rain survey. February 1072).

Questions req·niring a description

The reason behind the inclusion of descriptive questions in the questionnairohas been to gain some knowledge of a common' language' which may be usedwhen discussing vibration with non-scientific members of the travelling public.The lack of generally applicable words is a major drawback in the constructionof meaningful questions about vibration effects. To illustrate this point: in theaudiometric field the term' loudness ' is widely understood by all sectioru of thecommunity, as is the term' brightness' when discussing levels of illumina­tion. However, no such general term exists to describe either the intensityor the quality of a vibrational stimulus. From the descriptions obtained itseems, for example, that hovercraft passengers tended to describe the pre­dominant motion as ' bumpy' whereas the vibration in a helicopter was usually

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862 D. J. Oborne and Jl1. J. Clarke

described as a' judder' (see Table 1). It seems therefore, that the descriptionsof vibrational intensity are greatly influenced by the type of vibration experi­enced. (A predominantly high amplitude, low frequency motion wasexperienced in the hovercraft, as opposed to a low amplitude high frequencymotion in the helicopter). This situation is somewhat different to thatexperienced by workers in the audiometric field where any noise-regardlessof pitch--or waveform may still be reliably described on a scale of loudness.

Table 1. Descriptors of the motion given by hovercraft and helicopter passengers

Hovercraft % Helicopter %Description in terms ofa situational experience 51·2 Shake 3i·0Bumpy 22·i Juddcr 28·0Rolling 4·8 Bouncy 0·2, Up/down l motion 4·1 Bumpy (i·GVibration 3·5 Rough 5·3Pitching 3·1 Lurch 2·1Bouncy 2·8 Plunge 1·8Choppy 2·4 Heave 1·0Jerky 2'4Nauseating 2·4'Others 2·8

It must be noted that the questions, although asking for descriptions of the motion, werephrased differently in each caso. The hovercraft question was ofan open-ended type which merelyasked tho passengers to describe the motion they wore experiencing. The helicopter passengers,however, were given a list of descriptors and were asked to tick the one which was most appropriate.

Questions requiring a rating

In all of the surveys so far conducted at Swansea, questions requrrmgpassengers to provide numerical estimates of certain features of the environmenthave usually taken the form of an open rating line] 0 cm long bearing twoscale ends (e.g, Important-Not Important; Plcasanb-Unpleasant.). By thismethod, the passenger is asked to rate the factor under consideration (by puttinga cross on the line) in terms of the scale ends provided. Obvious precautionsneed to be taken to offset the tendency to rate towards the' good' or the' bad'end of the scale every time, and to ensure that the scale itself is unidimensional(i.e. to ensure ~hflt the scale is defining one attribute only-e.g. the scale c VeryComfortable-Y,ery Unpleasant' is not unidimensional as the passenger is beingasked to rate in terms of comfort and pleasantness). The subsequent analysisof this type of question is usually carried out by dividing the line into equalsections and calculating the proportion of passengers who rated in each section.Thus a frequency distribution is formed from which ' average' ratings findtheir respective dispersions may be computed.

For the reliable analysis of a rating line, however, one must have somenotion of the sensation being perceived by the passenger. Merely becauseoaoh pflssenger is rating the same external stimulus, one cannot assume thateach passenger is perceiving the same stimulus. For example, a passengermay be partially deaf, in which case his perceived stimulus may differ to thatof a passenger with normal hearing. In this case he will be rating a different

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Comfort Snrvey 863

perceived stimulus intensity to other passengers with the result that his ratingsmay adversely bias the final analysis. For this reason therefore, the ratinglines have been accompanied by a corresponding question asking the extentto which the factor under consideration is being perceived. For examplepassengers have been asked to state how loud they considered the noise to bein the carriage-' very loud', 'quite loud', 'moderate', 'fairly quiet', or, very quiet'. Such extra questions ensure that the analysis of the rating linesis effected in a meaningful manner.

A second pitfall in the use of rating lines lies in the choice of scale ends used,for different people may have a different conception of what they represent.To some people, for example, the scale end' pleasant' may connote a state ofrest only attainable in the most luxurious of cars; to others however, whomight have recently experienced an uncomfortable journey, the same termmight imply anything better than the previous journey. Such ambiguity indescriptive scale ends, therefore may lead to some passengers rating on anintrinsically different scale to that used by others, with a resultant high spreadin the combined ratings.

One means by which this problem has been reduced has been to replace theadjectival scale ends with short phrases denoting situational experiences­either those which the passenger might have himself experienced, or thosewhich he is well able to imagine. It could be argued of course, that by leavingthe scale definition to the imagination of the passenger, one creates the sameproblem as before. Such an argument, however, would be countered with theclaim that one is better able to imagine the experience of ' sitting in a sound­proofed room' than the abstract concept of 'pleasantness', and that thedifferences in interpretation would be less with the former than with the latterseale end.

A further extension of the subjective rating methods has lately been accom­plished by the use of a ' magnitude estimation' type of rating (see Figure 3).In this case, passengers were provided with two situations-' sitting in a sound­proofed room' and' standing next to a heavy lorry going uphill', and were toldthat the noise levels experienced in these situations were fixed at 0 and 100 unitsrespectively. They were then asked to ascribe a number (in terms of this scale)to the level of noise that they were experiencing at the time. Noise wasinitially chosen as the factor to be rated because it was also possible to measurethe noise level in the transport environment. The two scale ends were chosenafter a short study in which 10 subjects were asked to rank the followingsituai.ions in order of loudness.

(A) Standing next to a heavy lorry going uphill.(B) Standing next to a pneumatic drill in operation.(e) Being in a tube train.

(A) was consistently judged to be the loudest of the three.

To compare the two types of rating scale, half of the passengers on the secondDover hovercraft survey received the' magnitude estimation' question whilstthe other half (randomly interspersed) were asked to rate the noise level on [1

10 em line bearing the same scale ends (see Figure 3 and 4). The two distribu­tions obtained are shown in Figure 5 and the similarity between them is imme­diately observable.

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804 D. J. Oborne and J1I. J. Otarke

If on a scale of noise, the noise level encountered in

a sound-proofed room was 0, and that of standing next

to a heavy Lor-r-y going uphill was 100, what number

...-oul.d you give to the present level of noise experienced

in a moving hovercraft?

~.ll. You may go beyond 100 if you wish.

L--- - _

Figuf'O :l. The' magnitude estimation I type of question.

Below is a scale of noise levels encountered in

different situations, ranging from being in a sound-

proofed room (0) to standing next to a heavy lorry

going uphill (100). Please put, a cross on til", line

corresponding to "..here you would put the present

noise level that you arc now experiencing L;c , the

nc.ise in this moving hovercraft.

~.B. You may go beyond the end of the line if rou wish.

Sitting in a sound­proofed room

Standing next to aheavy lorry goinguphill

Figure 4. The' line rating ~ type of quest.ion

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"l'('spon~"

3()-39

Comfort Stu'vey

0----0 Line

I1agnitudeEs t Imat Ion

11.1 11 12 13 1-1 I';

110_Jl~ 130-13~1 150-1.)1)

Rating

8(jfi

Line

~l.lg'litude

LstllnJti,'1LCa tcgor-y

Eigufo fi. Comparison of ratings obtained from marking on a line and magnitude estimationquestions.

Questions designed to determine the type 0/ population sampled

Apart from the development of methods for obtaining numerical estimates,no questionnaire survey would be complete without discovering details of thetype of passengers sampled. For this reason, therefore, questions asking forthe respondents age, sex, occupation, reasons for travel, et c., are asked at thebeginning of the questionnaire. A further function of these questions (whichalways oecupy the first page) is to introduce the passenger to the questionnaireand thus to establish the rapport normally necessary between interviewer andrespondent. In spite of the personal nature of the questions and despitepredictions to the contrary by experts of questionnaire design (e.g. Oppenheim1966), however, the response rate to questions asking for such personal detailshas consistently remained very high. Overall, approximately 99% of thepassengers who completed the questionnaire stated their age and sex, and over90% furnished their oecupation. Such a high response rate is thought to beduo to the impersonal nature in which the questionnaire is distributed (i.e. it isleft with the respondent and collected later) and also to the fact that the anony­mity of the respondent was assured.

4. The Conclusions Drawn from the Surveys Conducted at SwanseaThe main conclusions to be drawn from the surveys conducted so far are

two-fold: Firstly, these studies have demonstrated the success of thequestionnaire as 101 tool for obtaining quite scientific information from a cross­section of the travelling public. This very fact alone signifies the usefulness ofthe technique for research in which information is required from a large numberof different persons. The questions, as presently worded, have been under­stood by most people of all age groups (the range so far sampled has been from

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Soo D. J. Oborne and M. J. Clarke

7 to 8(; years), and from all social classes. Furthermore, it has been the generalimpression thH,t thoro is a willingness on the part of the members of the publicto co-operate, and many passengers have expressed appreciation of the factthat they had been invited to comment on the environment within the vehicleconcerned. This indicates a further advantage of such questionnaire studies­that of establishing a favourable 'public relations' impression between thetransport operators and their customers.

Merely obtaining a high response rate and demonstrating the ability toadequately sample all members of society, however, is not proof enough of theefficacy of the questionnaire. Before its acceptance, the questions must beshown to provide reliable and valid results. The term reliability is generallytaken to indicate the degree of trustworthiness or stability of the questionitself, whereas the term validity indicates the uccuracu of the question inmeasuring what. it is intended to measure. As an example, the noise levelin a vehicle may be measured with almost perfect reliability in that it may bemeasured again and again and similar measurements be obtained. It haslittle validity, however, as an indication of the speed of the vehicle, and onlymoderate validity as an indication of its overall comfort.

A typical measure of the reliability of any test is to compare the scoresderived from the first half of the test with those derived from the second half(slllit-half reliability)-the assumption being that a reliable test would producesimilar scores in each half. To test the reliability of the rating line, therefore,an analysis was affected of the ratings obtained from the passengers on thesecond Dover hovercraft survey. These passengers had been asked to rate theextent to which they considered each of the environmental factors present inthe vehicle (the noise, temperature, seat comfort, cabin vibration and wavemotion) influcnced their feeling of comfort. They were asked to put a cross ona 10 em linc, which defined a scale ranging from' Not Influence' to ' GreatlyInfl uence '. I~ight hundred passengers had successfully answered this question,and thus the ratings obtained from the first 400 were compared with those ob­tained from the second set of 400 passengers. Because the first half of thesurvey period was effectively being compared with the second half, it was im­portant in the analysis to use only those factors whose intensity did not changeappreciably over the period of the whole survey. The only relevant factorwhich complied with this maxim, however, was that of noise and thus the twodistributions for this factor are shown in Figure 6. A Kolmogorov-Smirnovcomparison of the distributions (which effectively compares their cumulativefrequency distributions) indicates no statistical difference between the two.This observation indicates the high reliability of the rating line.

The validity of the rating line question, however, may only be shown bythe extent to which it is able to predict accurately, or correlate with, a corres­ponding external criterion-in this case the physical (objective) measure of thefactor. It is the difficulty in obtaining the objective measure of the factorunder consideration, however, which handicaps attempts at establishing suchvalidity. Ideally, the factor should be one which will alter in intensity overthe period of the survey in order that the ratings may be validated for the wholecontinuum. The only factor which has fulfilled this requirement in the pasthowever, has been that of the vehicular motion-a factor which until recentlyhas been difficult to measure effectively because of equipment malfunctioning.

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°/0 response

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oNotInfluence

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Figure 6. Ratings of the influence of noise on comfort, obtained. from the first. and second sets of400 passengers.

All of the other factors that have been studied (the noise, temperature, humidityete.) have remained relatively constant in intensity on the forms of transportso far investigated. In spite of the above, however, an indication of the validityof the technique may be obtained by comparing, in the second Dover hover­craft survey, ratings of the journey comfort (Very Comfortable-Very Un­comfortable), with the hovercraft captain's assessment of the sea height. Theincrease in the comfort rating (i.e. a decrease in subjective comfort) with seaheight may be seen in Figure 7 where, apart from a slight drop in the ratingaround a sea height of 4-5 ft, an obvious decrease in the perceived comfort maybe seen as the assessed sea height increases. Although such indicationsregarding the reliability and validity of the rating line technique are not meantin any way to be conclusive evidence of the usefulness of the techniques, it issuggested that they do provide grounds for future research and investigation.

Whereas the theme of this paper has been to argue for the usefulness ofsampling a great number of subjects by means of a questionnaire, it must beremembered that in doing so information (sometimes important information)may be lost or not obtained. This problem may be illustrated by reference toFigure 7. A drop in the comfort rating may be observed at sea height 4-5 ft,and this may have been due to a more experienced pilot taking the helm of thehovercraft. Such information, however, would be difficult to obtain and theconclusion would be even harder to substantiate.

The problem of ' averaging' might be cited as a further example of the lossof information which may occur in the analysis of the questionnaire surveys.

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Rfi8 D. J. Oborne and 11l. J. Clarke

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Mean comfortrat ing in ems.

Assessed Sea Height in feet.

Figure 7. The mean rnt.ing of comfort. versus the assessed sea height.

As an illustration, it is assumed that tile survey had been instigated because ofthe need for obtaining a large number of responses. For the quantificationof the data, therefore, one would assume that, initially at least, averagingtechniques (and their associated measures of dispersion) would be needed togive an indication of what thc ' average ' passenger is feeling. Such an analysis,however, docs not take into account other factors which may affect a passenger'srating. For exampie, in thc hovercraft it was well known that passengers whosat towards the front of the cmft were more exposed to the motion effects thanthose who were seated towards the rear. It was also obvious that different seaconditions affected the general 'ride' of the craft. :1<'01' a proper analysis,therefore, the passengers' responses should be subdivided into those who satforward and those who sat aft, and into those who experienced different weatherconditions. With further thought, it can be seen that further subdivisionsnceded to be made into the original sample size, with the result that the finalanalyses were carried out on much smaller (and thus less reliable) sample sizes.To a certain extent, of course, this problem may be alleviated by sampling amuch larger population but such a survcy would, of necessity, cover a longerperiod of timc and perhaps result in still further subdivisions.

The authors gratefully acknowledge the financial ussiatenee for this research from the ScienceResearch Council of Great Britain. Grateful thanks are also extended to Mrs Susan Oborne forassistance ill the analysis of questionnaire responses, and to D.E.A. Helicopters Ltd; BritishHail; and Sccepeed Ltd for allowing the surveys to take place on their vehicles.

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Comfort S7uvey S(iH

Los auteurs de oct ert.icle onf tcnt.e de montrer I'ut.ilite d'un qucst.ionna.irc pow' cvalucr leoonforf ressent.i par les passegers dans les moyens de transport, Un tel questionnaire a ete misau point it Swansea. Bien que I'Interpretanion des donnees foumiee par lo quest.ionnuire se heurteamaintcs clifflcult.es, it semble qu'une attention minut.iousc apportec A In construction et it I'analysedu questionnaire puisee fournir ties elements d'Inforrnat.ion interessauts pour des recherchesfutures, uinsi que pour une appreciation valable des sensations subjeet.ives resscnt.ics par leevoyageurs.

In diesel' Arboit haben die Autorcn vcrsucht, die Brauchharkcit des Fregebogens ala \Verkzeugfur die Gewinnung von Informut.ion tiber die Bequemlichkeit del' Passagiere durch diose selbstfestzustellen. Ein Swansea entwickelter angemesscncr Fragebogcn wurde n.ls Beispiel benutzt,\Venn auch hoi del' Interpretation del' Daten viele Fallgruhen cxistiercn, wird argumcnticrt, cluesbei sorgfaltiger Bewertung sowohl del' Anlage wie auch del' Analyse des Fragebogens niitzlicheInformation zu erhalten m6glich ist., Solche Information liesse eich als cin Lndikut.or fur weitercForschung und ale wertvollcr .Hinweis auf die subjekt.iven Geftihlc des Passugicrs gebrauchen.

ReferencesBRAN'.rON, P., 1972, Ergonomic research contributions to the design of passenger environment.

Paper -presented to the Institution of Mechanical Engi,ftccrs, Morch.: 1972.BRANTON, P., and GRAYSON, G., 1967, An evaluation of train seats by observation of sitting

behaviour. Ergono·m,ic8, 10,35.OPPEXHEDI. A. N., 1966, Questionnaire Design and A ttitude Measurement, (London: Hlo;IX:\IAXX.)

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