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Dutch MusculoskeletalQuestionnaire: descriptionand basic qualitiesV. H. Hildebrandt , P. M. Bongers , F. J. H. vanDijk , H. C. G. Kemper & J. DulPublished online: 09 Nov 2010.
To cite this article: V. H. Hildebrandt , P. M. Bongers , F. J. H. van Dijk , H. C.G. Kemper & J. Dul (2001) Dutch Musculoskeletal Questionnaire: description andbasic qualities, Ergonomics, 44:12, 1038-1055, DOI: 10.1080/00140130110087437
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Dutch Musculoskeletal Questionnaire: description and basicqualities
V. H. HILDEBRANDT{*, P. M. BONGERS{, F. J. H. VAN DIJK{, H. C. G. KEMPER} andJ. DUL}
{TNO Work and Employment, PO Box 718, 2130 AS Hoofddorp, TheNetherlands
{Coronel Laboratory, University of Ansterdam, Amsterdam, The Netherlands
}Institute for Research in Extramural Medicine (EMGO Institute), VrijeUniversiteit, Amsterdam, The Netherlands
}Erasmus Business Support centre, Rotterdam, The Netherlands
Keywords: Questionnaire; Musculoskeletal workload; Musculoskeletal symp-toms; Validity.
A questionnaire (`Dutch Musculoskeletal Questionnaire, DMQ) for the analysisof musculoskeletal workload and associated potential hazardous workingconditions as well as musculoskeletal symptoms in worker populations isdescribed and its qualities are explored using a database of 1575 workers invarious occupations who completed the questionnaire. The 63 questions onmusculoskeletal workload and associated potentially hazardous working condi-tions can be categorized into seven indices (force, dynamic and static load,repetitive load, climatic factors, vibration and ergonomic environmental factors).Together with four separate questions on standing, sitting, walking anduncomfortable postures, the indices constitute a brief overview of the mainndings on musculoskeletal workload and associated potentially hazardousworking conditions. Homogeneity of the indices is satisfactory. The divergentvalidity of the indices is fair when compared with an index of psychosocialworking conditions and discomfort during exposure to physical loads. Workergroups with contrasting musculoskeletal loads can be diVerentiated on the basisof the indices and other factors. With respect to the concurrent validity, it appearsthat most indices and factors show signicant associations with low back and/orneck shoulder symptoms. This questionnaire can be used as a simple and quickinventory for occupational health services to identify worker groups in which amore thorough ergonomic analysis is indicated.
1. IntroductionIn daily practice, occupational health and safety services and ergonomicconsultancies in companies often have to advise management on interventions toreduce musculoskeletal workload and related disorders. Because such interventionscan have a great impact on the company, a proper analysis is essential to select themost hazardous situations that require ergonomic interventions. Time and resources
*Author for correspondence. e-mail: [email protected]
ERGONOMICS, 2001, VOL. 44, NO. 12, 1038 1055
Ergonomics ISSN 0014-0139 print/ISSN 1366-584 7 online # 2001 Taylor & Francis Ltdhttp://www.tandf.co.uk/journalsDOI: 10.1080/0014013011008743 7
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to carry out comprehensive studies are often lacking. Therefore, occupationalphysicians, nurses, hygienists and ergonomists need simple and quick methods toobtain relevant information on work-related factors that contribute to themusculoskeletal workload and related disorders. On the basis of such screening,priorities can be set as to which worker groups or workplaces should be addressed ina more thorough ergonomic analysis.
A detailed measurement of musculoskeletal workload (postures, movements andforce exertions) by direct methods such as observations or inclinometry iscomplicated and time consuming when large worker groups are involved, andskilled analysts are needed for reliable measurements (Buckle 1987, Hagberg 1992,Kilbom 1994, Winkel and Matthiassen 1994). There is, therefore, a need for simplescreening instruments for identifying groups of workers at risk (jobs, departments,tasks, etc.) such as checklists (Keyserling et al. 1992), rating of physical jobrequirements (Buchholz et al. 1996), surveys (Bishu 1989) or periodic surveillance(Weel et al. 2000). Although the quantication of the absolute exposure levels has itslimitations using these methods, the information gathered can be su cient to rankgroups according to their levels of exposure (Burdorf 1999). A subsequent morelaborious detailed ergonomic analysis can be restricted to those workers andworkplaces that are identied as potentially hazardous during the rst screening.
A questionnaire as screening instrument has the great advantage that it yields notonly exposure data, but also information on associated health symptoms and onideas of workers themselves about possibilities for improvements. High symptomrates are important as well as high workload when setting priorities for furtheranalyses and development of solutions. In addition, participation of the workers isensured and thus the use of such a questionnaire ts very well into a participatoryapproach to ergonomic problems (Vink et al. 1992).
TNO (Netherlands Institute for Applied Scientic Research) developed aquestionnaire called the `Dutch Musculoskeletal Questionnaire (DMQ) to measurethe self-reported musculoskeletal workload and other associated hazardous workingconditions as well as related symptoms. This paper addresses the most importantaspects of the validity of this measuring instrument.
. Can the questionnaire constitute a clear-cut description of a particularworker population by a limited number of indices for diVerent types ofworkloads (convergent validity)?
. Do these indices show a relatively low correlation with indices that measure adiVerent adjacent concept, such as psychosocial working conditions and anindex of reported discomfort due to musculoskeletal load (divergentvalidity)?
. Can the questionnaire identify worker groups with relative high workload orother unfavourable working conditions (discriminative power)?
. Do the indices show a signicant association with musculoskeletalsymptoms, indicating that exposure to that load constitutes a risk ofsymptoms for the exposed workers (concurrent validity)?
The criterion-validity of the questionnaire with respect to the measurement ofmusculoskeletal workload and symptoms has been addressed elsewhere (Hildebrandtet al. 2001). This paper is restricted to addressing the convergent, divergent andconcurrent validity of the questionnaire.
1039Dutch Musculoskeletal Questionnaire
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2. Methods and materials2.1. DMQThe standard version of the questionnaire consists of nine pages with*25 questionsper page to be lled in by the workers themselves. Completion-time is *30 min.There is also a short version (four pages) and an extended version (14 pages)available. The following sections are distinguished.
. Background variables (e.g. age, gender, education, duration of employment,work history, shift work).
. Tasks (prevalence rates and perceived heaviness of task demands).
. Musculoskeletal workload (postures, forces, movements).
. Work pace and psychosocial working conditions (demands, control andautonomy, work organization and social support, work satisfaction), whichare factors which may play an important role for workers with musculoske-letal disorders (Bongers et al. 1993).
. Health, in particular musculoskeletal symptoms; the phrasing of questions onprevalence is comparable with the `Nordic Questionnaire on MusculoskeletalDisorders (Kuorinka et al. 1987), including the denition of areas of thebody pictorially and, in addition, the extended version contains more detailedquestions on the nature and severity of these symptoms.
. Lifestyle (e.g. sports, smoking) (in the extended version of the questionnaireonly).
. Perceived bottlenecks and ideas for improvements suggested by the workersthemselves (optional).
To enable experts to work with this questionnaire easily, a software package(LOQUEST) has been developed for data entry, data analysis and autoreport of themain results.
The basic concept behind the questionnaire is a simple representation of therelationship between work tasks and musculoskeletal symptoms (Dul et al. 1992,Paul 1993). Work-related musculoskeletal symptoms are explained by a high internalphysical load caused by postures, movements and force-exertions needed in the worktasks. Other factors, such as other working conditions, individual factors (gender,age), psychosocial aspects or lifestyle, can inuence these relationships on diVerentlevels. All these elements are measured in the diVerent parts of the questionnaire.
To ensure an optimal content validity of the questionnaire, the choice ofvariables to be measured was based on available reviews of the epidemiologicalliterature (Hildebrandt 1987, Walsh et al. 1989, Riihima ki 1991, Stock 1991). Thesereviews identied a large number of potentially harmful postures, movements, force-exertions and other potentially hazardous working conditions, which are still valid atthe present time (Bernard 1997, Hoogendoorn et al. 1999, Arie ns et al. 2000).
Musculoskeletal workload (postures, forces, movements) is addressed in 63questions (see table 2 for the phrasing of the questions). These questions can becategorized into the following six types of potentially hazardous workloads andworking conditions.
. Force exertions: lifting, carrying, supporting, pushing, pulling, pinching.
. Dynamic loads: walking, bending and twisting of trunk, neck or wrists,stooping, squatting, reaching.
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. Static loads: sitting, standing, prolonged bent or twisted posture of trunk,neck or wrists, working with hands above shoulder level, kneeling orsquatting posture.
. Peak loads: sudden, forceful movements, unexpected movements.
. Repetitive loads.
. Ergonomic environmental conditions: (1) climatic factors, (2) vibration, (3)limited working space and (4) slipping and falling on occasions.
The questions are formulated in such a way that they indicate the presence orabsence of exposure and not the amount of discomfort caused by the exposure,which is addressed in a separate part of the questionnaire. The preciseformulation was based on several eld studies where the preliminary versionsof the questionnaire were used. The exposures addressed in the questions werenot dened, explained or illustrated to limit the size of the questionnaire and thetime needed for completing it. No training was given on the completion of thequestionnaire. Given the goal of the questionnairea quick but comprehensivesurveyit was decided to use mostly dichotomous answering categories (yes/no).This qualitative approach, without attempts to quantify frequency and durationof variables, was also chosen because the validity of quantitative approaches byquestionnaire has been seriously questioned (Kumar 1993, Kilbom 1994, Winkeland Matthiassen 1994, Baty et al. 1986, Rossignol and Baetz 1987, Wiktorin etal. 1993, Viikari-Juntura et al. 1996). The completion of the questions asdescribed above does not generally give any problems, even in less educatedworker groups.
2.2. Study populationA group of 1575 workers in 24 occupations, who completed the questionnaireduring various studies, constituted the population and database for theanalyses. The occupations diVered strongly with respect to musculoskeletalworkload and associated hazardous working conditions, e.g. nurses (n=237),shipyard workers (186), o ce workers (93) and metal workers (69). Table 1shows the main characteristics of this worker population and the subgroupsmentioned.
Table 1. Descriptive data on the total study population and four occupational groups withinthis population.
All(n = 1575)
Nurses(n = 237)
Shipyard(n = 186)
O ce(n = 128)
Metal(n = 69)
Demographic factorsMean age (SD) 35 (9.7) 34 (7.9) 37 (11.2) 37 (9.0) 32 (8.5)Mean education level (1, low; 5, high)3.2 4.0 3.2 3.7 2.4% male gender 61 12 100 34 80Work factors :% Frequent uncomfortable postures 57 52 72 24 28% Frequent sitting at work 33 27 29 76 44% Frequent standing at work 66 63 83 4 78% Frequent walking at work 65 71 57 16 46
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Table2.
Questionsonworkload,associatedfactorloadingsandexplained
varianceofninefactors(principalcomponentsanalysiswithvarimax
rotation)
asmeasuredin
thetotalstudypopulation(n=1575).Onlyfactorloadings40.39are
given;allcorrelationsare
signicant(P50.05).
Factor
12
34
56
78
9
Eigenvalue
15.3
4.9
3.4
2.2
1.7
1.7
1.5
1.5
1.3
Explained
variance
(%)
23.9
7.7
5.3
3.4
2.7
2.7
2.3
2.3
2.0
Doyouin
work
often
have
to:
1.Liftheavyloads(m
ore
than5kg)?
.76
..
..
..
..
2.Pullorpush
heavyloads(m
ore
than5kg)?
.64
..
..
..
..
3.Carryheavy
loads(m
ore
than5kg)?
.67
..
..
..
..
Doyouin
work
often
have
tolift:
4.In
anaw
kwardposture?
.77
..
..
..
..
5.Withtheload
farfrom
thebody?
.64
..
..
..
..
6.Withtwistedtrunk?
.69
..
..
..
..
7.Withtheload
abovechestheight?
.48
..
..
..
..
8.Withaload
thatishard
tohold?
.60
..
..
..
..
9.Withaveryheavyload(m
ore
than
20kg)?
.67
..
..
..
..
Doyouin
yourwork
often
have
to:
10.Standforaprolongedtime?
..
..
..
..
.54
11.Sitforaprolonged
time?
..
..
..
..
7.64
12.Walk
foraprolonged
time?
..
..
..
..
.61
13.Stoopforaprolongedtime?
..55
..
..
..
.Doyouin
yourwork
often
have
to:
14.Bendslightlywithyourtrunk?
..
..
..
..60
.15.Bendheavilywithyourtrunk?
.46
.42
..
..
..
.16.Twistslightlywithyourtrunk?
..
..
..
..72
.17.Twistheavilywithyourtrunk?
..52
..
..
..
.18.Bendandtwistwithyourtrunk?
..44
..
..
..46
.Doyouin
work
often
have
to:
19.Work
inaslightlybentposture
foraprolonged
time?
..49
..
..
..
.20.Work
inaheavilybentposture
foraprolongedtime?
..70
..
..
..
.21.Work
inaslightlytwistedposture
foraprolongedtime?
..61
..
..
..
.22.Work
inaheavilytwistedposture
foraprolongedtime?
..74
..
..
..
.
continued
1042 V. H. Hildebrandt et al.
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Table2.
Continued
Factor
12
34
56
78
9
23.Work
inabentandtwistedpostureforaprolongedtime?
..72
..
..
..
.Doyouin
yourwork
often
haveto:
24.Reach
withyourhandsandarm
s?.
..
..
..
..
25.Hold
yourarm
under
yourshoulder-level?
..
..
..
..
.26.Hold
yourarm
atorabove
shoulder-level?
..
..
..47
..
.27.Exertforcewithyourhandsorarm
s?.47
..
..
..
..
28.
Makesm
allmovements
withhands/ngersatahigh
workpace?
..
..44
..
..
.
Doyouin
yourwork
often
haveto:
29.Bendyourneckforwards?
..
..
.62
..
..
30.Bendyourneckbackward?
..
..
..54
..
.31.Twistyourneck?
..
..
.59
..
..
32.Holdyourneckinaforwardbentpostureforaprolonged
time?
..
..
.58
..
..
33.
Hold
yourneck
inabackward
bentposture
fora
prolonged
time?
..
..
..59
..
.
34.Holdyourneckinatwistedpostureforaprolonged
time?
..45
..
.45
..
..
Doyouin
yourwork
often
haveto:
35.Bendyourwrists?
..
..
.51
..
..
36.Twistyourwrists?
..
..
.49
..
..
37.Hold
yourwristbentforaprolonged
time?
..
..
.47
.44
..
.38.Hold
yourwristtwistedforaprolongedtime?
..
..
.44
.45
..
.Doyouin
yourwork
often
haveto:
39.Work
inuncomfortablepostures?
.46
..
..
..
..
40.Work
inthesamepostures?
..
..54
..
..
.Doyouin
yourwork
often
haveto:
41.Alwaysmakethesamemovem
entswithyourtrunk?
..
..77
..
..
.42.Alwaysmakethesamemovem
entswithyourarms?
..
..86
..
..
.43.Always
makethesamemovem
entswithyourwrists?
..
..85
..
..
.
continued
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Table2.
Continued
Factor
12
34
56
78
9
44.Alwaysmakethesamemovem
entswithyourlegs?
..
..73
..
..
.Doyouin
yourwork
often
haveto:
45.Makesudden,unexpectedmovem
ents?
..
..
.45
..
..
46.Perform
short,butmaximalforce-exertions?
.56
..
..
..
..
47.Exertgreatforceontoolsormachinery?
..
..
..
..
.Doyouin
youwork
often
have:
48.Notenoughroom
aroundyouto
perform
yourwork
properly?
..
..
..
.66
..
49.Notenough
room
aboveyouto
perform
yourwork
withoutbending?
..
..
..
.52
..
Doyouin
yourwork
often
have:
50.Dicultyin
exertingenough
forcebecause
ofincomfor-
tablepostures?
..
..
..
.57
..
51.Toofewfacilities
toleanonduringwork?
..
..
..
.53
..
52.Troublein
reachingthingswithyourtools?
..
..
..
.51
..
53.Doyousometimes
slip
orfallduringyourwork?
..
.46
..
..
..
54.Doyouoften
havetopinch
withyourhandsduringwork?
..
..
..
..
.55.Do
you
inwork
experience
noticeable
vibrationsor
shocks?
..
..
..54
..
.
56.Doyoucarryvibratingtoolsduringyourwork?
..
..
..55
..
.57.Doyoudrivevehiclesduringwork?
.43
..57
..
..
..
58.Isyourwork
physicallyvery
taxing?
..
..
..
..
.59.Doyouin
yourwork
experience
draughts,wind?
..
.74
..
..
..
60.Doyouin
yourwork
experience
cold?
..
.81
..
..
..
61Doyouin
yourwork
experience
warm
th?
..
.43
..
..
..
62.Doyouinyourwork
experience
changesoftemperature?
..
.72
..
..
..
63.Doyouin
work
experience
humid
air?
..
.69
..
..
..
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2.3. AnalysisThe convergent validity was assessed by a principal component analysis (PCA), usedto construct a limited number of well-dened workload indices for diVerent types ofworkloads, which enables a clear-cut description of a particular worker population.Varimax rotation was applied to ensure minimal correlation between the indices(below). Homogeneity of the indices resulting from the PCA was assessed bycomputing Cronbachs a.
To explore the divergent validity of the indices, rst, the intercorrelation wascomputed between the seven indices and an index of psychosocial workingconditions (sum of 35 questions on demands, control and autonomy, organizationand social support, and work satisfaction). For a good divergent validity, the indicesshould show a relatively low correlation with indices which measure a diVerentadjacent concept, such as psychosocial working conditions. Next, the correlationbetween the indices of workload and an index of reported discomfort due tomusculoskeletal load was computed. The latter was constructed from 10 questionssuch as `Are you experiencing discomfort during sitting at work? These questionshad to be answered regardless of the amount of exposure. The correlation can givean indication of whether the exposure reported by the worker is severely biased bypossible discomfort experienced by the worker during the exposure to this load.
To analyse whether the seven indices could diVerentiate between occupationalgroups with contrasting workload, four specic subgroups (nurses, shipyardworkers, o ce workers and metal production workers) were analysed. For a gooddiscrimination, contrasts between these worker groups should be reproduced bydiVerences in the means of the indices. Means and 95% condence intervals (CI) ofthese indices were computed for each worker group according to the methoddescribed by Brand and Radder (1992), specically developed for indices that consistof dichotomous variables. DiVerences between worker groups were consideredsignicant (p5 0.05) when the computed condence intervals were not overlapping.
The concurrent validity was tested by assessing the relationships of the indices (asindependent variables) with musculoskeletal symptoms (as dependent variables) in amultiple logistic regression analysis on an individual level (see `concurrent validity in`results). For a good concurrent validity, the indices should show a signicantassociation with musculoskeletal symptoms, indicating that exposure to that loadconstitutes a risk of symptoms for the exposed workers. For this analysis, all indiceswere dichotomized into a low- and high-exposure level, with the cut-point at 50% ofthe population analysed. Twelve-month prevalence rates of symptoms (pain,discomfort) of the low back and of the neck shoulder area were taken as themeasure of eVect. These were measured with the same questionnaire (`Have you everhad trouble (ache, pain, discomfort) from your...). All the independent variableswere included simultaneously in the model and were thus adjusted for the others.Age was entered in the model as a possible confounder. Estimated odds ratios (OR)are presented as the measure of association. OR 4 1 indicates that the index isassociated with a higher prevalence rate of symptoms and is considered statisticallysignicant when the 95% CI do not include 1.
3. Results3.1. Construction of indicesTable 2 shows the result of the PCA. Table 3 shows the tentative descriptions of thecontent of these factors. A nine-factor model explained 52% of the total variance.
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Table3.
Nam
e,content,Cronbachsa ,meanscore
andSD
ofsevenindices
andfourseparatequestions(n=1575).
Nam
eContent
n*
amean**
SD
1Forceexertion
lifting,pushingandpulling,forcefulmovementswitharm
s,highphysical
exertion,liftinginunfavourablepostures,liftingwiththeload
awayfrom
thebody,liftingwithtwistedtrunk,liftingwithloadsabovethechest,
liftingwithbadgrip,liftingwithvery
heavyloads,shortforceexertions,
exertinggreat
forceonhands
13
.90
4.8
3.1
2Dynamicloads
trunk
movem
ents
(bending
and/or
twisting),
movem
ents
ofneck,
shouldersorwrists,reaching,
makingsudden
and/orunexpectedmove-
ments,pinching,workingunder,atoraboveshoulder
level
12
.83
5.9
2.7
3Staticloads
lightlybentandtwistedtrunkposture,heavilybentandtwistedtrunk
posture,bentandtwistedposturesofneckorwrists
11
.87
3.9
2.8
4.
Repetitiveloads
workingin
thesamepostures,makingthesamemovem
entswithtrunk,
arm
s,hands,wristsorlegs,makingsm
allmovem
entswithhandsatahigh
pace
6.85
4.8
3.4
5Ergonomic
environment
availableworkingspace,lack
ofsupport,slipingandfalling,troublewith
reachingthingswithtools,notenough
room
aboveto
perform
work
withoutbending
6.78
3.1
3.0
6Vibration
wholebodyvibration,vibratingtools,driving
3.57
1.8
2.7
7Climate
cold,draught,changesin
temperature,moisture
4.84
4.8
4.0
Uncomfortable
postures
havingoften
todealwithuncomfortableposturesat
work
1-
--
Sitting
sittingoften
atwork
1-
--
Standing
standingoften
atwork
1-
--
Walking
walkingoften
atwork
1-
--
Overallindex
indices
17
55
.95
4.5
2.3
*Numberofquestions.Themaximumscoreequalsthenumberofquestionsintheindex
andcorrespondsto
apositiveanswerto
allquestionsinthe
index.Thehigher
themeanscore,thehigher
theself-reported
exposure.
**Allindices
are
standardized
onamaximum
of10to
enhance
comparability.
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From tables 2 and 3, it can be concluded that to a great extent the PCA supports thetypes of workload formulated above upon the literature: force exertions (representedmainly by factor 1), dynamic loads (represented mainly by factors 5 and 8), staticloads (represented mainly by factors 2 and 6), repetitive loads (represented by factor4) and ergonomic environmental factors (represented by factors 3 and 7) can bedistinguished. Only peak loads are not represented by a separate factor: they arerepresented by factor 5 (sudden, unexpected movements) as well as by some parts offactor 1 (sudden, forceful movements). Furthermore, dynamic and static loads arediVerentiated for trunk (factors 2 and 8) and neck shoulder arm (factors 5 and 6).Ergonomic environmental factors are diVerentiated into two factors (3 and 7),whereas vibration is not identied as a separate factor, but is included in factor 6.Since walking, standing, sitting and uncomfortable postures are di cult to assign toone of the above-mentioned factors, it seems logical to consider these factors as fourindependent factors.
The PCA thus results in seven `indices of workload and other working conditionsand four separate questions on standing, walking, sitting and uncomfortablepostures. Table 3 shows the description, content and homogeneity (measured withCronbachs a) of the indices and an overall index of musculoskeletal load (as the sumof all seven indices). Six out of seven as are 40.80, which indicates a satisfactoryaverage inter-item correlation.
3.2. Divergent validityTable 4 shows the intercorrelations between the seven indices of workload and otherworking conditions, the four separate factors, the overall index of workload, anindex of psychosocial working conditions (a=0.82), an index of reporteddiscomfort due to musculoskeletal load (a=0.85), and age.The correlation between the indices of workload and the index of psychosocialworking conditions varied between 0.21 and 0.33 and was thus in most cases lowerthan the correlations between the indices of workload themselves, which varied from0.26 to 0.74. Correlation of the workload indices with the index of reporteddiscomfort due to musculoskeletal loads varied between 0.19 and 0.61 and wasrelatively high for the indices force, dynamic load and static load. Correlation withage was low (varying between 0.01 and 0.17).
Table 4 also shows that correlations between the indices force, dynamic load, andstatic load were relatively high (0.59 0.74).
3.3. DiVerentiation of worker groupsFigures 1a and b show the means of all indices and factors for the four selectedworker groups (nurses, shipyard workers, o ce workers and metal productionworkers).
The data show that worker groups can be diVerentiated: each group can bedescribed specically. Shipyard workers show the highest means of exposures to mostindices and o ce workers the lowest (except for sitting, walking and repetitive loads).
3.4. Concurrent validityTables 5a and b show the results of the multiple logistic regression for symptoms ofthe low back and neck shoulder regions.
In particular high force exertion, high static loads, unfavourable ergonomicenvironmental conditions and uncomfortable postures are signicantly associated
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Table4.
Correlationmatrixofseven
indicesofmusculoskeletalworkloadandassociated
potentialhazardousworkingconditions(17)andfourseparate
factors(811)andoverallindex
(12),psychosocialworkingconditions(13)1,reported
discomfortfrommusculoskeletalworkload(14),andage
(15)
computedforthetotalstudy-population(n=1575).
12
34
56
78
910
11
1213
1415
1Force
2
Dynamicload
.64
3
Staticload
.59
.74
4
Repetitiveload
.35
.52
.59
5
Ergonomicenvironment
.60
.48
.54
.37
6
Vibrations
.42
.26
.30
.33
.42
7
Climate
.44
.32
.40
.34
.47
.48
8
Uncomfortablepostures
.57
.55
.61
.25
.42
.22
.32
9
Sitting
.10
.06
.02
.14
.03*
.12
.01*
.06
10
Standing
.39
.37
.43
.31
.29
.13
.23
.24
.12
11
Walking
.32
.39
.24
.11
.18
.10
.10
.06
.17
.42
12
Overallindex
.82
.83
.87
.68
.71
.48
.58
.61
.03*
.41
.28
13
Psychosocialworking
conditions1
.33
.27
.31
.29
.33
.24
.21
.23
.21
.12
.05
.41
14Reported
discomfort
.51
.53
.61
.39
.45
.19
.30
.48
.02*
.32
.18
.61
.33
15
Age
.02*
.02*
.05
.06
.07
.10
.17
.01*
.08
.03*
.03*
.09
.08
.06
*Notsignicant(P5
0.05).
1Cluster
ofdichotomousquestionsonpsychosocialwork
aspects;ahigher
score
indicates
more
problems.
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Figure 1a. Means and 95% CI of self-reported exposure summarized in seven indices ofmusculoskeletal workload and potential hazardous working conditions, for fouroccupations (1=nurses; 2=shipyard workers; 3=o ce workers; 4=metal productionworkers). No data were available on the repetitive index for metal production workers.
Figure 1b. Means and 95% CI of self-reported exposure to uncomfortable postures, sitting,standing and walking, for four occupations (1=nurses; 2=shipyard workers; 3=o ceworkers; 4=metal production workers).
dynamicload
staticload
1 2 3 41 2 3 4
climatevibrationsergonomicenviron-ment
repetitiveload
1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4
10
8
6
4
2
0
a
force
b
1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4
uncomfortablepostures
sitting standing walking
100
80
60
40
20
0
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with low back symptoms. High repetitive loads and uncomfortable postures areassociated with neckshoulder symptoms. Vibration and walking are associated withfewer symptoms of the neck shoulder region.
4. Discussion4.1. Convergent validityIn theory, an instrument used to identify risk groups with respect to musculoskeletaldisorders, with the aim of taking eVective preventive measures, should contain onlyitems that show a prospective relation with musculoskeletal symptoms or sick leavedue to musculoskeletal symptoms. Subsequent interventions in the high-risk groupsidentied should be eVective with respect to the reduction of musculoskeletalmorbidity and/or disability. Unfortunately, it appears to be very di cult as yet toidentify the items which show a prospective relation with musculoskeletal disordersor sick leave due to musculoskeletal disorders; recent reviews and epidemiologicalstudies indicate that there are still many questions on the roleand particularly thequantitative importanceof relevant workload factors and intervening variables inthe causation of musculoskeletal symptoms and disability (Kilbom 1994, Feuersteinet al. 1999). They also indicate that only a small proportion of the total variance isexplained (Frank et al. 1995), that there is still little evidence that elimination of
Table 5a. Estimated odds ratios (OR) and 95% condence intervals (CI) in the multiplelogistic regression analysis of seven indices of workload and age on symptoms of low backand neckshoulder (n=1575).
Low back Neck shoulder
OR 95% CI* OR 95% CI*
Force 1.54* 1.172.02 1.09 0.821.43Dynamic load 1.14 0.851.53 1.29 0.971.74Static load 1.33* 1.021.76 1.23 0.941.62Repetitive load 1.13 0.871.45 1.50* 1.161.92Vibrations 0.73* 0.550.96 0.72* 0.550.96Adverse climate 0.89 0.681.18 1.09 0.831.44Ergonomic environment 1.39* 1.061.83 1.17 0.891.54Age 0.79* 0.631.01 1.18 0.931.48
*P5 0.05
Table 5b. Estimated odds ratios (OR) and 95% condence intervals (CI) in the multiplelogistic regression analysis of uncomfortable postures, standing, sitting, walking and ageon symptoms of low back and neckshoulder (n=1575).
Low back Neck shoulder
OR 95% CI* OR 95% CI*
Uncomfortable postures 2.49* 2.003.08 1.95* 1.582.42Standing 1.10 0.861.43 1.15 0.891.48Sitting 1.10 0.871.40 1.22 0.981.52Walking 1.06* 0.841.34 0.75* 0.570.92Age 70.79* 0.630.98 1.23 0.991.53
*P5 0.05
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ergonomically hazardous work reduces the number of disorders (Bernacki et al.1999) and that our current knowledge of risk factors is largely based on studies withmoderate-to-low quality scores (Viikari-Juntura and Riihima ki 1999). Nevertheless,recent systematic reviews do provide strong evidence for manual materials handling,bending and twisting, and whole-body vibration as risk factors for low back painand moderate evidence for patient handling and heavy physical work as risk factorsfor back pain (Hoogendoorn et al. 1999) as well as some evidence for the duration ofsitting, twisting or bending of the trunk, neck exion, arm force, arm posture, hand arm vibration and workplace design as risk factors for neck pain (Ariens et al. 2000).
Insu cient or invalid exposure measurement may be a major explanation for theremaining gaps in our knowledge (Winkel and Matthiassen 1994). As a consequence,the questionnaire incorporated a large number of potentially harmful postures,movements, force exertions and other potentially hazardous working conditions,which are believed to be important risk factors on the basis of anatomical ,physiological, biomechanical, psychophysiologica l or ergonomic ndings, despitelacking epidemiological evidence. This was also reason for performing anexploratory factor analysis, since it would have been di cult to formulate explicitlya xed number of factors and expected allocation of items. Nevertheless, the factoranalysis conrmed to a large extent the concept that formed the basis for thegeneration of the questions. Force, dynamic and static loads, repetitive movementsand ergonomic environmental factors were identied as separate entities. It shouldbe noted that the correlations between most factors stayed rather high, but this couldbe expected since all factors are based on self-reported data and most workingsituations are characterized by combinations of exposures rather than by a singlehomogeneous exposure. Further aggregation of indices with high intercorrelationswas considered inappropriate since it would merge characteristics of the work whichare really diVerent from an ergonomic point of view.
Since the factor `ergonomic environment contained several quite diVerententities, it was decided to distinguish three factors: poor climate, vibration andergonomic environment sensu stricto, the last factor representing in particular spaceconstraints leading to unfavourable postures. Furthermore, some important factorsthat describe elementary postures or movements (standing, walking, sitting) oruncomfortable postures appeared to be quite independent from the other indices andwere therefore considered as separate factors. `Uncomfortable postures probablymeasures discomfort instead of exposure, which explains its added value with respectto the indices of physical loads.
4.2. Divergent validityAn important question about the usefulness of the DMQ in ergonomic practice iswhether the indices measure actual musculoskeletal workload and not other workdimensions, such as psychosocial work factors or reported discomfort. Thecorrelation of the indices with the index of psychosocial working conditions israther low (*0.30) but signicant and thus shows some degree of association, but atthe same time also a substantial degree of divergence (a fair divergent validity). Thesignicant correlations (between 0.19 and 0.61) of the musculoskeletal workloadindices with the index of reported discomfort indicates an association between thereport of exposure and the presence of discomfort due to the exposure; thisunderlines the importance of diVerentiating as far as possible between self-reportedexposures and self-reported discomfort during exposures. Literature is somewhat
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conicting on the question of whether self-reported exposures are biased bydiscomfort during these exposures or by the presence of musculoskeletal symptoms.Some studies indicate such a relation (Ryan 1989), while others do not (Riihima ki etal. 1989). Given the quite strong correlation between those two dimensions found inthis study, the conclusion seems justied that the indices can measure exposure tomusculoskeletal workload and associated potentially hazardous working conditionsonly to a certain extent: one has to be aware that the reported exposures may beinuenced by reported discomfort, at least at an individual level.
By using PCA with varimax rotation, the independence of resulting factors wasassured, but this was partly undone by subsequent alterations of the factors to denethe ultimate indices: the resulting intercorrelations between the indices are fairly highin some cases, but they show enough unexplained variance to be considered asseparate dimensions of musculoskeletal workload and associated potentiallyhazardous working conditions (a fair convergent validity).
4.3. Identifying worker groups at riskThe analyses of the four subgroups with contrasting workloads showed that workergroups with contrasting workloads could be identied. This is an essential feature inaccordance with the intended use of the questionnaire: identifying high-risk groups.However, it is obvious that the questionnaire cannot diVerentiate between workergroups with insu cient contrast in workload. In addition, the diVerentiation willalways be `relative (ranking groups relative to each other), since no criteria can beformulated as yet to dene `high and `low exposures on the basis of the qualitativedata of a questionnaire.
It is well established that job title is generally a poor proxy for describingexposures to ergonomic risk factors and that variance can be high within a job title(Burdorf 1992, Hagberg 1992, Li and Buckle 1999). Thus, the associations foundbetween the indices and other measures are probably an underestimation of risks,since the involvement of really homogeneous worker groups would probably resultin a better diVerentiation.
4.4. Concurrent validityAs had been expected on the basis of the literature, most indices showassociations with the symptoms, indicating the relevance and predictive validityof the indices in varying worker groups. In particular, `uncomfortable posturesshowed relatively high ORs both for low back symptoms and for neck shouldersymptoms. Since `discomfort may be regarded as an early manifestation ofsymptoms or disorders, the high ORs could be expected. Nevertheless, inaddition to the independence of this indicator from the other indices, this suggeststhat this indicator might be a very relevant variable for the diVerentiation ofworker groups.
All associations are in agreement with the literature, with the exception of thenegative association between vibration and symptoms for both the low back andneck shoulder, which is di cult to explain, since whole-body vibration isconsidered as a major risk factor for these symptoms (Bovenzi and Hulshof1999). Exposure to vibration is limited to a few specic worker groups (e.g. metalworkers, shipyard workers) with specic exposures to hand-arm vibration andpossibly a healthy worker selection eVect in these groups could explain, at leastpartly, this nding.
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The strength of the (cross-sectional) associations found is in agreement withother studies (Riihima ki et al. 1989, Hagberg 1992, Tsai et al. 1992) and is wellfounded considering the prevalence measure used and the high prevalence rates ofsymptoms in the unexposed groups.
5. ConclusionsThe DMQ enables a global assessment of musculoskeletal workload and otherpotentially hazardous working conditions by seven homogeneous indices (forces,dynamic loads, static loads, repetitive loads, climatic factors, vibration andergonomic environmental factors) and four separate factors (sitting, standing,walking, uncomfortable postures). With these indices, worker groups withcontrasting musculoskeletal workloads and associated potentially hazardous work-ing conditions can be diVerentiated. Most indices show signicant associations withlow back and/or neck shoulder symptoms. These indices can, therefore, be used asone of the means to identify risk groups and can supply experts in occupationalhealth and safety services and ergonomic consultancies with data for determiningpriorities concerning ergonomic improvements among worker groups.
An English translation of the DMQ can be downloaded from the website of TNOWork and Employment: www.workandhealth.org
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