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    ERGONONUCS

    1993,

    VOL

    36,

    NO

    6, 627-644

    Decision making style driving style and self reported involvement in

    road traffic accidents

    D.

    J. FRENCH,

    R.

    J. WEST,J. ELANDERnd J. M. WILDING

    Psychology Department, Royal Holloway and Bedford New College, University of London,

    Egham, Surrey TW20 OEX, UK

    Keywords

    Driving; Accident involvement; Survey; Questionnaire; Decision-making; Driving

    style.

    In an exploratory postal survey of 711 drivers stratified by age, sex, annual

    mileage, and accident involvement, decision-making style was measured using a

    Decision-Making Questionnaire (DMQ) and driving style was assessed using a

    Driving Style Questionnaire (DSQ). Responses to 21 items of the DMQ formed

    seven independent and internally coherent dimensions according to a principal

    components (PC) analysis. These were labelled: control, thoroughness,

    instinctiveness, social resistance, hesitancy, perfectionism, and idealism. PC

    analysis also revealed that responses to 15 items of the DSQ formed six

    independent dimensions of driving style. These were labelled: speed, calmness,

    social resistance, focus, planning, and deviance. Multiple regression analysis

    indicated that drivers of 60 years and under who scored lower on thoroughness

    were at greater risk of a traffic accident and that this relationship was mediated by

    faster driving. This relationship was independent of age, sex, annual mileage, and

    all other factors measured. In the drivers over 60 years, lower thoroughness,

    greater hesitancy, and faster driving were independently associated with higher

    accident rates independent of all other factors measured. The results provide

    preliminary support for the view that people import aspects of their general

    decision-making style into the driving situation, and that in so doing they put

    themselves at differential risk of having a road traffic accident.

    1. Introduction

    Previous research has in general failed to reveal an association between psychomotor

    ability and road traffic accident rates (Goldstein

    1961).

    Factors which have emerged

    as predictors of accident involvement (taking account of annual mileage) include age,

    experience, ability to detect hazards quickly and tendency towards risk taking

    (Brown and Groeger 1988, Jonah 1986, Mayhew

    et al

    1981, Quimby

    et al

    1986). It

    may be that differential accident involvement has more to do with the way that

    people make judgements and decisions than merely ability to control the car, e.g., the

    decision to overtake, change lanes, accept a gap of a particular size when parking, etc.

    Thus it seems plausible that decision-making would be a useful focus for research

    efforts aimed at understanding differential accident involvement.

    There are two main ways of approaching the study of decision-making. One is to

    examine the beliefs and values that enter into the decision process (e.g., Edwards

    1954, Fishbein and Ajzen 1975). This has been the subject of much research in

    psychology. The other is to examine the style of decision-making, i.e., the way that

    individuals habitually approach decision problems and use information. Little

    research has been directed at this latter issue. The present research programme was

    designed to investigate possible relationships between decision-making style and

    road traffic accident liability. A major feature of this approach has been to collect

    information about general aspects of decision-making and relate these to accident

    ()()14-0139/93 1O ()()

    1993 Taylor

    Francis Ltd.

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    628

    D French

    et al.

    liability by looking at the way that they are reflected in driving style e.g., choice of

    speed).

    Style of decision-making involves those aspects of the decision process in which

    individuals may be presumed to adopt a common mode of operation across a wide

    range of decision domains. Thus for the concept to apply there must be cross

    situational stability. Examples of decision-making style may be: how far individuals

    are prepared to examine the pros and cons of various options before making up their

    minds; the level of risk that they will accept in return for an optimum outcome; and

    the relative importance of emotions in making a decision which could be reached

    analytically.

    There are several existing questionnaire measures of decision-making style. One of

    these Buck and Daniels 1984) was developed from Harren s 1979) Model of Career

    Decision-Making. Individuals are characterized by scores on one of three scales:

    rational, intuitive, or dependent. Rational decision-makers seek relevant information,

    look carefully at future consequences, and act deliberately and logically. Those who are

    intuitive in their decision-making show little anticipation of future consequences or

    systematic information-seeking. Dependent decision makers do not take

    responsibility for their decisions, but take the path of least resistance, having a high

    need for social approval. Arroba 1977) devised a classification of decision-making

    which was applied subsequently to career decision-making by Hesketh 1982).

    Arroba s taxonomy was derived by interviewing subjects regarding recent decisions

    that they had made; six styles of decision-making emerged. These were emotional,

    intuitive, rational, hesitant, compliant, and no-thought. The six styles were found to

    fall along an active-passive continuum, with rational and hesitant being the most

    active and compliant the least active. Hesketh found that one year after careers

    counselling, subjects who had reported a rational decision-making style were most

    likely to have achieved a match between their aspirations and their current situation,

    whereas emotional and compliant individuals were least likely to have done so.

    Johnson 1978) has proposed a more general theory of decision-making style, but

    this too has been investigated and reported only in the context of careers counselling.

    It proposes two independent aspects of decision-making style; information gathering

    and information analysis. Information may be gathered spontaneously or

    systematically and analysed internally or externally. A questionnaire, the Johnson

    Decision-Making Inventory JDMI-Johnson

    et al

    1983), has been designed to

    assess these dimensions.

    Gordon

    et al

    1986) studied the relationship between Johnson s dimensions and

    Harren s styles, which were assessed using the Assessment of Career Decision

    Making Scale ACDMS-Buck and Daniels 1984). A factor analysis of the scale

    scores, three from the ACDMS and four from the JDMI, showed that the first factor

    was identified by strong positive loadings for systematic John son) and rational

    Harren) and an equally high negative loading for intuitive Harren). The second

    factor was characterized by positive loadings for external and spontaneous Johnson)

    and dependent Harren). The third factor was Johnson s internal.

    The link between Johnson s and Harren s inventories suggests that, by self-report

    at least, there is an identifiable trait of decision-making style; conceptual similarities

    between these and Arroba s 1977) taxonomy support this conclusion. Had Arroba s

    styles been included in Gordon

    et al s

    investigation, one might have expected further

    factors to emerge, indicating that neither the JDMI nor the ACDMS are identifying

    the full range of decision-making styles.

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    Decision making and RTAs

    629

    All of the above attempts to characterize decisions and decision makers have

    potential contributions to make to a comprehensive account of individual

    differences in decision-making style. However, there is no comprehensive decision

    making questionnaire available.

    This paper reports the development of a questionnaire measuring general

    decision-making style and its relationship with driving behaviour, also measured by

    questionnaire, and involvement in road traffic accidents. The ultimate aim was to

    trace a path from certain aspects of decision-making style to differential likelihood of

    accident involvement.

    2. Methods

    2 1 Materials

    In order to develop a questionnaire on decision-making style, a number of ways in

    which the decision process might differ were generated. Some of these corresponded

    to dimensions used in questionnaires already in existence. Thus Johnson s

    internal/external distinction and the compliant and dependent dimensions were

    represented by items about preference for consultation and advice and susceptibility

    to social pressure. The emotional and logical versus intuitive categories were

    reflected in questions about the role of feelings in decision-making.

    Questions were also added asking about locus of control Rotter 1966). In

    addition, examination of normative theories of decision-making Simon 1957, Janis

    and Mann 1977, Edwards 1954) led to consideration of depth of search through

    consequences of courses of action, breadth of search through different options,

    degree of planning ahead, use of principled versus pragmatic solutions, use of

    satisficing versus optimizing decision rules, risk acceptance, degree of certainty about

    a decision, and level of commitment to it.

    Several versions of a questionnaire containing items relating to these dimensions

    were tested and items deleted or modified according to whether subjects appeared to

    be able and willing to answer them consistently and informatively.

    This resulted in a 30-item Decision-Making Questionnaire DMQ). DMQ items

    were phrased as questions asking about frequency of a given type of behaviour and

    subjects were instructed to tick one of six boxes that indicated that they behaved in

    this way: never or very infrequently, infrequently, quite infrequently, quite

    frequently, frequently, very frequently or always.

    A questionnaire about driving style was also developed. The choice of items for

    inclusion was based on behaviours that had previously been shown, or were

    suspected, lo be related to accident involvement or risky driving behaviour. These

    were speed Wasielewski 1984), headway distance to the car in front-Evans and

    Wasielewski 1983), seat belt use Evans et al 1982), gap acceptance size of gap in the

    flow of traffic before attempting to pull out-Bottom and Ashworth 1978), and traffic

    light violations Koneci et al 1976). In addition, the questionnaire included items

    about behaviours thought to be directly related to decision-making style. For

    example, specific questions about feeling in control when driving, some of which

    were based on Montag and Comrey s 1987) scale of driving internality and

    externality which proved to have a reliable factor structure, were included. Questions

    were also asked about reactions to advice when driving, route planning, and risk

    taking on the road. Responses were on the same six-point scale of frequency as the

    decision-making questionnaire.

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    630

    D. French et al.

    The DMQ and driving style questionnaires were put together in a package which

    also included questions about biographical details, miles driven annually and

    accident involvement during the previous year. Data on accident involvement for up

    to three years prior to this was available from a questionnaire previously completed

    by the same subjects see below).

    2.2. Subjects and procedures

    The questionnaire package was sent to 980 drivers in all parts of the UK. The sample

    was a subset of 30 000 drivers who had previously been randomly selected from those

    licensed at the Driver and Vehicle Licensing Agency DVLA) Swansea to take part in

    a questionnaire survey conducted by National Opinion Polls for the Transport and

    Road Research Laboratory. In the survey, they gave details of their driving habits

    and accident records for the past three years, as well as personal details, and at the

    end indicated whether they would be willing to help with further research. The data

    gathered during this exercise provided information necessary for stratification ofthe

    sample selected for this study by age, sex, annual mileage and accident involvement.

    Thus our sample was not representative of the population at large, but it enabled us

    to take account of the relationship of exposure, age, and sex with accident rates.

    Table 1 shows the stratification of the sample.

    Table 1.

    tratification of the sample.

    ge

    8-24

    25-590+Low

    o accid.

    0

    0

    5

    2: 1 accid.

    00

    5

    No accid.

    0

    0

    5

    2: 1 accid.

    00

    5

    Lowo accid.00

    4

    2:1 accid.

    005

    No accid.

    005 2: 1 accid.

    0

    06

    ales-

    ow mileage

    =

    1-10765 miles p.a.

    high mileage> 10765 miles p.a.emales-Iow mileage

    =

    1-4848 miles p.a.

    igh mileage>4848 miles p.a.

    Completed questionnaires were returned by 711 drivers, 73 of those who were

    sent one. There was a tendency for a slightly higher response rate among older

    subjects chi squared

    714 with 2 degrees of freedom,

    p

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    Decision making and RTAs

    6

    (3) assessment of the internal coherence and derivation of subscales for the

    Driving Style Questionnaire (DSQ);

    (4) investigation ofrelationships between DSQ scores and age and sex;

    (5) investigation of relationship between decision-making and driving style and

    accident rates;

    (6) modelling of the role of decision-making style and driving style in the

    causation of accidents using multiple regression.

    Some of the variables used in the analyses did not conform to a normal distribution

    therefore differences and correlations were analysed using both parametric and non

    parametric methods, with near identical results. For the purposes of presentation

    parametric statistics arereported throughout. In tests of significance, two-tailed tests

    were used unless otherwise indicated.

    3. sults

    3 1 Internal coherence and derivation of subscale scoresfor the DMQ

    A principal components analysis of the DMQ yielded seven components with

    eigenvalues greater than one. Together they accounted for 543 of the variance.

    These seven independent dimensions were interpreted by examining the contents of

    the variables loading highly upon them. Table 2 shows the item loadings on each of

    the components after varimax rotation. A criterion of 04 as used as the minimum

    loading for an item to be incorporated in a dimension. Nine of the 30 items did not

    meet this criterion for any dimension and were excluded from further analysis. The

    Table 2. Items loading on the dimensions of decision-making style.

    Factor

    I. Thoroughness

    (179 of variance)

    2. Control

    (95 of variance)

    3. Hesitancy

    (79 of variance)

    4. Social resistance

    (65 of variance)

    5. Perfectionism

    (58 of variance)

    6. Idealism

    (52 of variance)

    7. Instinctiveness

    (50 of variance)

    *Item abbreviated.

    Loadings

    079

    -070

    065

    064

    076

    075

    072

    -058

    -045

    070

    057

    055

    070

    -057

    055

    070

    069

    080

    -069

    067

    061

    Items

    Do you work out all the pros and cons?*

    Do you decide without considering all the implications?*

    Do you plan well ahead?

    Is your decision-making deliberate and logical?*

    Do you remain calm?*

    Do you enjoy making decisions?

    Do you feel in control of things?

    Do you avoid making decisions if you can?*

    Do you find it difficult to think c1early?*

    Do you favour first one option then another?*

    Do you change your mind about things?

    Do you take the safe option if there is one?

    Do you avoid taking advice over decisions?

    Do you like to consult with others?

    Do you make up your own mind about things?*

    Do you carry on looking for something better?*

    Do you settle for an option that will just about do?*

    Are practicalities more important than principles?*

    Are your decisions governed by your ideals?*

    Do you rely on gut feeling when making decisions?

    Do you stick by your decisions come what may?

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    632

    FIG 1a CONTROL

    SUBSCALE SCORE

    30

    I

    SEM

    8

    26

    French et al.

    FIG 1b THOROUGHNESS

    SUBSCALE SCORE

    5

    I SEM

    3

    21

    24

    22

    //

    /-..j

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    FIG 1e PERFECTIONISM

    Decision making and RTAs

    FIG 11IDEALISM

    633

    SUBSC ALE SCORE

    15~------

    I S.EN

    13

    11

    9

    ~

    SUBSC ALE SCORE

    15 ~,-----~-----------~

    I S.EM

    13

    11

    9

    - /: >

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    634

    D.

    J.

    French

    et al.

    elationships of decision-making dimensions with age and sex.

    Correlation

    Males scores

    emales scores

    n=343

    n=366

    value for

    n=709

    ean

    D

    ean

    D

    ex difference 020***

    77168216108

    015***

    3413

    2216

    49*** -014***12

    14

    1-315

    091

    008

    515

    415062

    -014***9

    19

    9

    19020

    017***6

    187

    17

    076

    009**

    2

    17

    617

    2 79**

    *p

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    FIG 2a SPEED

    Decision making and RTAs

    FIG 2b CALMNESS

    635

    SUBSCALE SCORE

    15

    I SEM

    13

    SUBSCALE SCORE

    20 I - - - - -- - - - - -- - - - - --~

    I

    SE.M.

    18

    11

    16

    9

    +-,

    +----+

    ,

    ,

    ,

    ,

    +----+..,

    ,+

    14

    12

    ~

    /

    /

    -+---+- _-I

    v --,+--

    10 ~I-~--~-~ __ __L __ _'_ __ _'__ _ __1

    5

    2 3 4

    AGE CATEGORY

    - MALES -+ FEMALES

    FIG 20 PLANNING

    3 4 5

    AGE CATEGORY

    - MALES

    -+.

    FEMALES

    FIG 2d FOCUS

    6

    SUBSCALE SCORE

    15

    I S.E.M

    13

    11

    SUBSCALE SCORE

    20,--------------------,

    I SEM.

    18

    16

    9

    -+----+

    /,

    /

    /

    +-_---1

    14

    12

    ~-+

    *---+-- //

    -

    +---- //

    2 3 4 5

    AGE CATEGORY

    - MALES -+. FEMALES

    10

    3 4

    AGE CATEGORY

    - MALES -+ FEMALES

    6

    3 3 Internal coherence and derivation of subscale scoresfor the DSQ

    A principal components analysis of the driving style questions revealed six

    components accounting for 394 of the variance. The six dimensions were

    interpreted as speed (made up of items about driving fast and exceeding the speed

    limit), calmness (items about staying calm in dangerous situations and when there is

    little time to think), planning (consulting a map and planning places to stop and rest

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    636

    FIG 2e SOCIAL RESISTANCE

    D J French

    et al.

    FIG 21 DEVIANCE

    SUBSCALE SCORE

    15

    r-------------------,

    I S.E.M.

    13

    11

    9

    -~--- .-

    - -

    ..... , --

    -

    ,

    ,

    ---

    SUBSCALE SCORE

    10

    r-------------------~

    I S.EM

    8

    6

    4

    ~- --

    r- __ _..I

    __ --

    r-- _ _..J......_

    -- -

    2 3 4 5

    AGE CATEGORY

    - MALES -+ FEMALES

    6

    I

    o~ -~-~-~-~~-~-~-

    3 4 5

    AGE CATEGORY

    - MALES

    -+

    FEMALES

    Figure 2. Driving Style Questionnaire DSQ) subscale scores broken down by age group and

    sex. Age group 1= 17-19; 2=20-29; 3=30-39; 4=40-49; 5=50-59; 6=60 and over.

    before setting out), focus driving cautiously and ignoring distractions), social

    resistance disliking being given advice about driving), and deviance jumping the

    lights and overtaking on the inside). Table 4 shows the dimensions, the percentage of

    variance that they accounted for and the item loadings. As with the DMQ, subscale

    scores were calculated for driving style dime.,,:sionsby reversing the coding of ratings

    with negative loadings and then adding up the items with loadings greater than 04.

    Also, as with the DMQ, separate principal components analyses were carried out on

    two randomly-selected subsamples each comprising half of the full sample. The

    resulting loadings were similar in both subsamples and both were similar to the

    results of the analysis on the full sample, indicating a stable structure.

    3 4 Relationships between DSQ scores and age and sex

    The relationship between each driving style dimension and age and sex was tested

    using Pearson s

    R

    correlations to investigate changes with age and

    t tests

    to look at

    the sex differences. In the case of deviance and planning scores, we also examined

    relationships in which these variables had been recoded into dichotomies to avoid

    the problem of undue influence of extreme scores. The results were nearly identical to

    those using the untransformed variables so, for the sake of presentational

    consistency, we report the simple Pearson correlations here. The mean-scores for

    each age group of males and females on each dimension were examined in order to

    establish the nature of the relationships. Figure 2 shows the results graphically. Table

    5 shows the correlations with age, and the sex differences in the driving style

    dimensions.

    Speed showed a steady decrease with age in both sexes and females scored lower

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    D.

    J.

    French

    et al.

    measure. The annualized accident rate for the three years prior to our study (the total

    number of accidents divided by the reporting period in years), as determined by the

    NOP survey which preceded ours (see section 2), was correlated with the rate during

    the following year as assessed by our postal questionnaire. This yielded an

    R

    of

    O

    305

    (p

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    Decision-making and RTAs

    639

    Fig 3a Drivers aged 60 and under

    -.12 p

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    D French et al.

    Table 8. Correlations of age, sex, mileage, and DMQ subscale scores with speed in 60s and

    under and over 60s.

    60 yrs

    Thoroughness

    Hesitancy

    Resistance

    Perfectionism

    Idealism

    Instinctiveness

    Age

    Sex

    Mileage

    p

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    Decision making and RT s

    641

    thoroughness appeared to be mediated by speed.

    the over 60s, speed,

    thoroughness, and hesitancy all played an independent role, and speed was predicted

    by instinctiveness.

    Part of the purpose of this study was to obtain a preliminary assessment of the

    concept of decision-making style. We found that respondents to a self-report

    questionnaire about their decision-making style gave answers which revealed quite a

    large number of different dimensions. This contrasts with the theories of Harren

    1979), Arroba 1977) and Johnson 1978). It is possible that there may be more than

    the seven which emerged from our questionnaire, but on our data there are unlikely

    to be fewer. The difference between our results and those of the studies emerging

    from the previous theories is probably due to the fact that the DMQ canvassed a

    much more diverse set of possible behaviours than did the previous questionnaires.

    One of the major dimensions which emerged from the DMQ corresponded to

    important aspects of the previous theories: the thoroughness dimension is similar to

    the rational styles of Harren and Arroba and the systematic style of Johnson.

    However, there can be little doubt that this is only one of many aspects of decision

    making.

    These data represent only the first step of a process of development and

    validation of both the concept of decision-making style and its measurement. It is

    one thing for self-reports of decision-making behaviour to be explicable in terms of a

    set of dimensions such as we have proposed. It is another to show that the behaviour

    itself can be thus explained.

    According to our drivers self-reported behaviour they did carry their global

    decision-making style into the driving situation. This offers the possibility that

    important aspects of driving behaviour can be understood in terms of more generally

    applicable traits that drivers may have. At a theoretical level it provides a way of

    linking theories of driver behaviour with more general theories of cognition and

    motivation. At a practical level it offers the possibility that aspects of driver

    behaviour can be indexed in situations, from the respondent s point of view,

    unrelated to driving. This may turn out to be useful if assessment of driver

    characteristics becomes used in real-life settings which have implications for

    individual drivers.

    It is only possible to speculate at this stage what might underlie the relationships

    between thoroughness and preferred driving speed in drivers of 60 and under. One

    obvious possibility is that low thoroughness is a reflection of a more global trait of

    impatience. It is not difficult to see how impatience might lead people to drive faster.

    One aspect of the Type A behaviour pattern involves a feeling of being under

    continual time pressure and this may too be related to impatience.

    this regard it is

    interesting that one study has examined the relationship between Type A behaviour

    and accident liability and found a positive relationship Perry 1986). To the extent

    that extroversion and sensation-seeking also involve impatience, this factor may also

    explain association between these variables and accident liability Pestonjee and

    Singh 1980). Further research along these lines will be needed to dissect out the key

    variable or variables here.

    The direct association of hesitancy and thoroughness with accident rates in the

    over 60s must be mediated by some aspects of driving style which we have not

    measured or not measured adequately). It may be that for drivers of this age, ability

    to process information rapidly is impaired Rabbitt 1991) and that if they do not

    allow for this by being more deliberate in their decision-making, or if it results in

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    French

    et al.

    them beginning manoeuvres and changing their mind this could raise their accident

    risk. As regards the relationship between instinctiveness and speed in the older

    drivers, it may be that a greater feeling ofthe infallibility of one s intuitive judgement

    could cause drivers to fail to appreciate the risks they run by driving at higher speed.

    Our observation of a link between self-reported driving speed and accident rates

    is consistent with the findings of other studies Engel and Thomsen 1988, Wilson and

    Greensmith 1983). Accident rates are a very imprecise measure of accident liability

    as demonstrated by the low correlation between accident rates over two successive

    periods. fact the correlation between speed and accident rates was not much less

    than the correlation between accident rates measured over two periods. Thus the

    importance of speed as a contributory factor to accident liability cannot be

    overstated; faster drivers are relatively unsafe drivers. Our self-reported dimension

    of speed has been shown in another study to correlate quite well with actual driving

    speed.

    the study concerned West et al 1993), the self-reported speed dimension

    of the DSQ correlated 055 with the judgements of drivers preferred speed made by

    two independent in-car observers during a mixed motorway and urban test route.

    that study observed speed also correlated positively with accident rates. Thus, the

    relationship between speed and accident liability is consistent and is not an artifact

    of our self-report methodology.

    The most plausible explanation for the relationship between driving speed and

    accident liability is that a direct causal link exists between the two. Minor

    misjudgements of distance or timing and unexpected hazards such as patches of ice

    on the road are turned into accidents because of excess speed. However, there are

    other possibilities which cannot be ruled out. It may be, for example, that faster

    drivers engage in particular driving habits which put them at risk. For example, they

    may pull out into smaller gaps than other drivers or attend less to the driving task.

    Further research is needed to unravel the various possibilities. This may involve

    obtaining further data about aspects of driving that are associated with speed, finding

    out whether there are certain kinds of accidents to which faster drivers are

    particularly susceptible, and assessing whether interventions directed at individual

    drivers to reduce their speed reduces their accident rates.

    Although deviant driving behaviour correlated significantly with accident rates,

    in the multiple regression analysis it was not shown to play an independent role.

    Current research indicates that a substantial number of accidents do occur as a direct

    result of deviant driving Reason

    et al

    1991). However, in our sample they were

    relatively uncommon. This may have been due to deviant drivers being less likely to

    volunteer for the study. It is also possible that the deviant drivers were unwilling to

    report their accidents. Finally, it is possible that there was under-reporting of deviant

    driving behaviour. All these factors would act to attenuate the relationship between

    self-reported deviant driving and accident rates. The possibility remains, however,

    that in the totality of accident statistics, excess speed is a more important factor than

    dangerous manoeuvres and that to the extent that traits of fast driving and deviant

    driving are separable, fast driving may play a greater role.

    Questionnaire methods such as have been used in this study can only be expected

    to provide a broad indication of relationships between variables of interest. They

    depend on respondents being able to form impressions of their own behaviour and

    communicate these using a fixed response format. Thus error of measurement is

    likely to limit severely the size of associations. Most of the correlations reported in

    this study were low, but reached high levels of statistical significance by virtue ofthe

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    large sample size. Thus, while the pattern of associations point the way towards

    potentially important relationships and ultimately to a theory of accident causation,

    for the practical prediction of accident rates, it will be necessary to develop and refine

    the measures used, perhaps supplementing self-report questionnaires with other

    forms of behavioural assessment. We have already mentioned the use of direct

    observation of dl-iver behaviour. We are also examining ways of using computerized

    tasks and presentation of real and hypothetical decisions as a means of assessing

    decision-making style.

    There is the danger when questionnaire responses are correlated with other

    questionnaire responses, that at least part of the associations found reflect

    consistency in response biases rather than underlying psychological dimensions of

    interest. It is difficult to envisage how response biases could lie behind the particular

    pattern of associations we found. The relatively large number of independent

    dimensions of decision-making and driving style, and the relationships between

    particular dimensions and accident rates would require a much more elaborate

    conception of response biases than has been proposed in the literature.

    In conclusion, this study has provided preliminary evidence on a new

    questionnaire assessing decision-making style indicating that at least seven

    independent dimensions can be isolated. One of these dimensions, which we have

    labelled thoroughness, correlated significantly with accident rates. In drivers of 60

    and under, this relationship appeared to be mediated by a single aspect of driving

    style, preferred driving speed. The results suggest several further lines of

    investigation which would help to provide a clearer understanding of why some

    drivers have more accidents than others.

    Acknowledgement

    The work described in this paper was carried out under a contract placed with Royal

    Holloway and Bedford New College by the Transport and Road Research

    Laboratory, Crowthorne, Berkshire and the paper is published by permission of the

    Director. The views expressed in this paper are not necessarily those of the

    Department of Transport.

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    Received 12 October 1990.

    Final revison accepted 8 November 1991.