Validity and reliability of the Brazilian version of the Work Ability Index questionnaire

Transcription

1 Rev Súde Públic 2009;4() Mri Crmen Mrtinez I Mri do Rosário Dis de Oliveir Ltorre II Frid Mrin Fischer III Vlidity nd relibility of the Brzilin version of the Work Ability Index questionnire ABSTRACT OBJECTIVE: To evlute the vlidity nd relibility of the Portuguese lnguge version of work bility index. METHODS: Cross sectionl survey of smple of workers from n electricl compny in the stte of So Pulo, Southestern Brzil (spred cross ten municiplities in the Cmpins re), crried out in The following spects of the Brzilin version of the Work Ability Index were evluted: construct vlidity, using fctoril explortory nlysis, nd discriminnt cpcity, by compring men Work Ability Index scores in two groups with different bsenteeism levels; criterion vlidity, by determining the correltion between self-reported helth nd Work Ability Index score; nd relibility, using Cronbch s lph to determine the internl consistency of the questionnire. RESULTS: Fctoril nlysis indicted three fctors in the work bility construct: issues pertining to mentl resources (20.6% of the vrince), self-perceived work bility (18.9% of the vrince), nd presence of diseses nd helth-relted limittions (18.4% of the vrince). The index ws cpble of discriminting workers ccording to levels of bsenteeism, identifying significntly lower (p<0.0001) men score mong subjects with high bsenteeism (7.2 points) when compred to those with low bsenteeism (42. points). Criterion vlidity nlysis showed correltion between the index nd ll dimensions of helth sttus nlyzed (p<0.0001). Relibility of the index ws high, with Cronbch s lph of CONCLUSIONS: The Brzilin version of the Work Ability Index showed stisfctory psychometric properties with respect to construct vlidity, thus constituting n pproprite option for evluting work bility in both individul nd popultion-bsed settings. I Núcleo de Epidemiologi. Hospitl Smritno de São Pulo. São Pulo, SP, Brsil II Deprtmento de Epidemiologi. Fculdde de Súde Públic. Universidde de São Pulo (FSP-USP). São Pulo, SP, Brsil DESCRIPTORS: Work Cpcity Evlution. Working Conditions. Questionnires. Trnsltions. Vlidity of Tests. Reproducibility of Results. Occuptionl Helth. III Deprtmento de Súde Ambientl. FSP- USP. São Pulo, SP, Brsil Correspondence: Mri Crmen Mrtinez Av. Conselheiro Brotero, 1505, cj. 2 - Higienópolis São Pulo, SP, Brsil E-mil: mcmrti@uol.com.br Received: 04/07/2008 Revised: 09/0/2008 Approved: 10/12/2008 INTRODUCTION Beginning in the 1980 s, s result of the geing of the working popultion in the context of restructuring of the production process, issues pertining to functionl geing hve become priority in the field of worker helth. 6, Work bility hs since then become n importnt indictor, for it encompsses spects Cost G. Some considertions bout ging, shift work nd work bility. In: Cost G, Goedhrd WJA, Ilmrinen J, editors. Interntionl Congress Series. Proceedings of the 2nd Interntionl Symposium in work bility: ssessment nd promotion of work bility, helth nd well-being of geing workers; 2004 Oct 18-20; Veron, Itly. Amsterdm: Elsevier. 2005; 1280:67-72.

2 2 Vlidity nd relibility of WAI Mrtinez MC et l of physicl helth, psychosocil wellbeing, individul competence, nd work conditions. The concept of work bility results from the combintion of humn resources in the context of the physicl, mentl, nd socil demnds of work, orgniztionl culture, nd work environment. 7 This concept cn be formulted s how well worker is or will be in the present or ner future, nd how cpble this worker is of performing work given the demnds of the job nd the helth sttus nd mentl nd physicl cpbilities of the worker. 18 Functionl geing is understood s reduction in work bility, nd my precede chronologicl geing, depending on the level of demnd. 17 The Work Ability Index (WAI) is n instrument tht llows for the evlution of work bility from the perspective of the worker s own perception, bsed on ten questions tht ddress seven dimensions: (1) current work bility compred with the lifetime best, with score rnging from 0 to 10 points; (2) work bility in reltion to the demnds of the job, bsed on two questions on the nture of work (physicl, mentl, or mixed) tht, when weighted, yield score rnging from 2 to 10 points; () number of current diseses dignosed by physicin, obtined bsed on list of 51 diseses tht defines score rnging from 1 to 7 points; (4) estimted work impirment due to diseses, bsed on question with score rnging from 1 to 6 points; (5) sick leve during the pst yer (12 months), bsed on question on the number of bsences, ctegorized into five groups with score rnging from 1 to 5 points; (6) own prognosis of work bility two yers from now, bsed on question with score rnging from 1 to 4 points; nd (7) mentl resources, bsed on score rnging from 1 to 4 points obtined by weighting the nswers to three questions. The results of these seven dimensions provide mesure of work bility tht rnges from 7 to 49 points. Instructions for clculting the score re vilble in Tuomi et l (2005). 18 This questionnire ws elborted bsed on studies crried out in Finlnd, where cohort of workers ws followed between 1981 nd 1992 to investigte issues of work bility bsed on the stress-strin theoreticl model. 9 According to this model, the distress generted by the physicl nd mentl demnds of work cn led to reduction in work bility nd trigger diseses. 9,20 These studies hve consolidted the theoreticl bses of the mjor determinnts, consequences, nd interventions of work bility nd served s bsis for the development of the underlying structure of WAI, which llows for evlution nd erly detection of ltertions nd cn subsidize the design of preventive mesures. 6,7,16 In Brzil, studies of work bility begn to be conducted following the trnsltion nd dpttion of the WAI questionnire for use in this country. 18 Certin ltertions were mde to the text of the instrument s n ttempt to ensure tht ll questions would be understood nd tht the questionnire could be self-dministered by ny subject who completed t lest the fourth-grde of elementry eduction. 18 The Brzilin version of WAI cn be found in Tuomi et l (2005). 18 Since its dpttion for use in Brzil in the lte 1990 s, the WAI questionnire hs been employed in severl popultion-bsed surveys. 1,5,1,19 However, the psychometric properties of the Brzilin version hve not yet been investigted. The present study ws imed t ssessing the vlidity nd relibility of the psychometric properties of the Brzilin version of the Work Ability Index. METHODS We conducted cross-sectionl study whose trget popultion comprised individuls working in the energy trnsmission, dvnced energy distribution sttions, nd humn resources sectors of n electricl utility compny in the re of the municiplity of Cmpins, Southestern Brzil. Of the 582 workers tht constituted the trget popultion, 9 (6.7%) workers who were on leve, chnging function, or on vction t the time of dt collection were excluded. Of the 54 remining subjects, 22 were in trining outside the compny, trvelling on business, or could not be locted, totling 521 vilble workers (89.5% of the originl popultion). Of these, 21 either did not respond or refused to prticipte in the study refusl rte of 4.0% nd 25 questionnires were left incomplete. Our finl smple thus included (87.5%) out of 54 eligible workers. An nlysis of losses showed no difference in terms of sex (8.5% losses mong women nd 12.9% mong men; p=0.85), work sector (14.6% in the dministrtive sector; 12.5% in the energy distribution sector, nd 10.5% in the energy trnsmission sector; p=0.70), nd time in the job (men 12.9 yers in the compny mong prticipnts nd 12.4 yers mong losses; p=0.548). There ws sttisticlly significnt difference in ge between prticipnts nd losses (men ge 7.5 nd 9.7 yers, respectively; p=0.00). We believe tht this difference would be unlikely to influence our results, nd therefore regrd the smple s representtive of the studied popultion. Dt collection ws crried out t the workplce, between August nd September For dt collection, Ilmrinen J. Towrds longer worklife! Ageing nd the qulity of worklife in the Europen Union. Helsinki: Finnish Institute of Occuptionl Helth. Ministry of Socil Affirs nd Helth; p.12-48

3 Rev Súde Públic 2009;4() we employed questionnire with items ddressing demogrphic nd functionl chrcteristics in ddition to the WAI nd the Medicl Outcomes Study 6 Item short form helth survey (SF-6) questionnires. To determine the psychometric properties of this version of WAI, we chose to evlute vlidity of construct nd criterion. Content vlidity ws not evluted, since this ws ddressed during the stges of trnsltion nd trnsculturl dpttion of WAI for use in Brzil. To determine construct vlidity, we crried out confirmtory fctor nlysis through principl component nlysis, selecting fctors with eigenvlues greter thn 1 nd correltion coefficients greter thn 0.50, using the vrimx method for mtrix rottion. This nlysis ws imed t determining whether predicted WAI dimensions would be confirmed in this popultion. We crried out discriminnt vlidity nlysis by compring men scores of groups of workers with high or low sickness-relted bsenteeism, using the Mnn-Whitney test. Informtion on bsenteeism ws obtined from the sickness-relted work bsence dimension of WAI. We considered s with low bsenteeism workers who reported up to nine missed workdys in 12-month period, nd s with high bsenteeism workers who reported missing ten or more dys in the sme period. These cutoff points were determined bsed on the question s response ctegories (zero dys, up to nine dys, ten to 24 dys, 25 to 99 dys, nd 100 to 65 dys), defined in the structure of the questionnire. 22 Criterion vlidity ws evluted by determining the correltion between WAI scores nd helth-relted vribles mesured using SF-6, using the Spermn correltion coefficient. WAI includes helth-relted vribles within its scope, nd is predictor of medium nd long-term worker helth. 18, We chose SF-6 s our stndrd criterion becuse it llows for n evlution of overll helth bsed on the subject s own perception, generting eight scores tht rnge from 0 to 100 points, representing the concepts most frequently mesured in helth surveys: physicl functioning, role-physicl, bodily pin, generl helth, vitlity, socil functioning, role-emotionl, nd mentl helth. WAI relibility ws determined by nlysis of internl consistency mong its items, using Cronbch s lph coefficient. We crried out Kolmogorv-Smirnov nlysis to determine dherence of the WAI score to norml distribution, nd subsequent sttisticl tests were chosen bsed on the result of this nlysis. For ll nlyses, we dopted the 5% significnce level. All clcultions were performed using SPSS version 10.0 softwre. This study ws pproved by the Ethics Committee of the Fculdde de Súde Públic d Universidde de São Pulo. Worker prticiption ws voluntry nd ll subjects signed term of free informed consent. RESULTS The study popultion consisted predominntly of mles (90.9%), mrried or with prtner (75.2%), nd with complete secondry (64.6%) or university eduction (26.7%). Men ge ws 6.8 yers (sd=8.0), rnging from 18.0 to 56.0 yers, with medin of 7.0 yers. Work ws predominntly of mixed nture (77.9%), with no workers crrying out predominntly physicl tsks. Men WAI score ws 41.8 points (sd=5.1), rnging from 1.0 to 49.0 points nd with medin of 4.0 points. This vrible ws not normlly distributed (p<0.0001, Kolmogorov-Smirnov test), determining the use of nonprmetric tests in subsequent nlyses. Tble 1 shows the following results for the different WAI dimensions: for current work bility compred with the lifetime best, 86.% of workers clssified themselves in the three highest scores. For work bility in reltion to the demnds of the job, 86.1% of workers plced themselves in the three highest scores. For number of current diseses dignosed by physicin, 6.6% of workers reported bsence of disese (7 points) nd 8.4% reported five or more diseses (1 point). For estimted work impirment due to diseses, 57.5% of workers reported no hindrnce/disese ffecting their work bility (6 points). For sick leve during the pst yer (12 months), 59.8% of workers reported no bsence from work due to disese in the lst 12 months (5 points). For own prognosis of work bility two yers from now, 89.1% of workers considered themselves very likely to be ble to perform their current ctivities in two yers time (7 points). For mentl resources, 65.1% of workers were in the highest score in the three mentl resources scles (bility to pprecite dily ctivities, perception of being ctive nd lert, feeling of hope for the future). Tble 2 shows tht principl component nlysis selected three fctors with cumultive totl vrince of 57.9%. The first fctor (20.6% of totl vrince) consisted of questions H, I, nd J, which represent the mentl resources dimension. The second fctor (18.9% of vrince) comprised questions A, B, nd C, on the worker s perception of his or her work bility. The third fctor (18.4% of vrince) ws composed of questions D, E, F, nd G, which ssess the presence of diseses nd helth-relted restrictions. Ilmrinen J, Tuomi K, Seitsmo J. New dimensions of work bility. In: Cost G, Goedhrd WJA, Ilmrinen J, editors. Interntionl Congress Series. Proceedings of the 2nd Interntionl Symposium in work bility: ssessment nd promotion of work bility, helth nd well-being of geing workers; 2004 Oct 18-20; Veron, Itly. Amsterdm: Elsevier. 2005; 1280:-7.

4 4 Vlidity nd relibility of WAI Mrtinez MC et l Tble 1. Distribution of the study popultion ccording to score in the different dimensions of the Brzilin version of the Work Ability Index. Are of the municiplity of Cmpins, Southestern Brzil, WAI dimension Current work bility compred with the lifetime best Work bility in reltion to the demnds of the job Number of current diseses dignosed by physicin Estimted work impirment due to diseses Sick leve during the pst yer (12 months) Own prognosis regrding of work bility two yers from now Mentl resources Score n (%) Totl 1 (0.2) - (-) - (-) (0.6) - (-) - (-) - (-) - (-) 40 (8.4) (0.6) 8 (1.7) 21 (4.4) 5 (1.1) 0 (6.) (0.6) 11 (2.) 25 (5.) 51 (10.7) 1 (2.7) 27 (5.7) 16 (28.6) 2 (0.4) 2 (0.4) 64 (1.5) 79 (16.6) 145 (0.5) 1 (6.5) 09 (65.1) 9 (1.9) 2 (0.4) 116 (24.4) 104 (21.9) 284 (59.8) 10 (2.1) 21 (4.4) 27 (57.5) 5 (11.2) 41 (8.6) 174 (6.6) 42 (89.1) Note: gryed-out cells re blnk becuse these scores do not exist for the respective dimensions. WAI: Work Ability Index 158 (.) 14 (0.1) 16 (28.6) 11 (2.8) 10 (21.7) 15 (2.2) Tble 2. Principl component nlysis of the Brzilin version of the Work Ability Index. Are of the municiplity of Cmpins, Southestern Brzil, Question Component 1 2 A Current work bility compred with the lifetime best B Current work bility in reltion to physicl demnds C Current work bility in reltion to mentl demnds D Number of current diseses dignosed by physicin E Estimted work impirment due to diseses F Sick leve during the pst yer (12 months) G Own prognosis regrding of work bility two yers from now H Enjoying dily tsks I Activity nd life spirit J Optimistic bout the future Vrince of the component (%) Totl cumultive vrince (%) 57.9 Men WAI score ws higher mong workers with low bsenteeism (42. points) thn mong those with high bsenteeism (7.2 points), nd this difference ws sttisticlly significnt (p<0.001), distinguishing groups of workers s to their level of disese-relted work bsenteeism. WAI showed sttisticlly significnt correltion with the eight dimensions of helth sttus nlyzed (p<0.001), with better helth sttus being correlted with higher WAI score (Tble ). The Cronbch s lph coefficient for WAI ws Exclusion of ny of the questions did not lter this result (Tble 4). DISCUSSION Issues pertining to work bility hve gined in importnce in the field of public helth due to their individul, socil, nd economic implictions. The contribution of WAI to the study of work bility is relted to its Cost G. Some considertions bout ging, shift work nd work bility. In: Cost G, Goedhrd WJA, Ilmrinen J, editors. Interntionl Congress Series. Proceedings of the 2nd Interntionl Symposium in work bility: ssessment nd promotion of work bility, helth nd wellbeing of geing workers; 2004 Oct 18-20; Veron, Itly. Amsterdm: Elsevier. 2005; 1280:67-72.

5 Rev Súde Públic 2009;4() 5 predictive vlue in terms of disbility, helth/disese, nd mortlity. 17, Our evlution of construct vlidity using fctoril nlysis showed tht the questions included in WAI cn be grouped into three components tht empiriclly confirm the work bility construct, understood s the bility worker hs to crry out his or her duties, nd which is strongly influenced by the worker s physicl nd mentl helth. 18,b An evlution of the psychometric properties of WAI in popultion of bout 8 thousnd nurses from ten Europen countries showed tht the fctoril structure of WAI hd two principl components in eight countries nd one principl component in one country. The uthors considered the first of these components to represent the subjective evlution of work bility nd the worker s mentl resources, nd the second to represent self-perceived helth sttus nd sickness-relted bsenteeism. b Still with regrd to construct vlidity, in this study we evluted discriminnt vlidity bsed on comprison between groups with different bsenteeism ptterns. Workers with limittions in work bility showed greter bsenteeism thn other workers. 10 Our results indicte tht WAI is cpble of discriminting between groups with different ptterns of bsenteeism. Workers with greter bsenteeism showed worse work bility scores thn other workers, confirming the vlidity of the Brzilin version. However, our results differ from those reported in the study of Europen nurses, where there ws no reltionship between sickness-relted bsenteeism nd work bility. b Construct vlidity is considered s the primry form of vlidtion of n instrument designed to mesure qulittive dt, given tht it tests the hypothesis of legitimte nd pproprite representtion of the construct by the instrument. 8,14 In the present study, the Brzilin version of WAI showed stisfctory construct vlidity, nd higher discrimintory power thn versions from other countries. The gretest difficulty with respect to criterion vlidity is obtining criterion for comprison considered vlid for mesuring subjective spects. 8,14 We regrded helth sttus s proxy for work bility given its mjor role in determining such bility. Deteriortion nd improvement in helth sttus represent, respectively, risk nd the possibility of further developing work bility. b,c We Tble. Spermn correltion coefficients for the Brzilin version of the Work Ability Index, ccording to helth sttus dimensions. Are of the municiplity of Cmpins, Southestern Brzil, Dimension n r p Physicl functioning <0.001 Role-physicl <0.001 Bodily pin <0.001 Generl helth <0.001 Vitlity 0.9 <0.001 Socil functioning 0. <0.001 Role-emotionl <0.001 Mentl helth 0.40 <0.001 Tble 4. Cronbch s lph per question for the Brzilin version of the Work Ability Index. Are of the municiplity of Cmpins, Southestern Brzil, Cronbch s lph Question when question is excluded Current work bility compred with the lifetime best 0.68 Current work bility in reltion to physicl demnds 0.69 Current work bility in reltion to mentl demnds 0.71 Number of current diseses dignosed by physicin 0.74 Estimted work impirment due to diseses 0.68 Sick leve during the pst yer (12 months) 0.71 Own prognosis regrding of work bility two yers from now 0.72 Enjoying dily tsks 0.70 Activity nd life spirit 0.70 Optimistic bout the future 0.70 WAI (ll questions) 0.72 chose to use self-evluted mesure of helth tht is vlidted strtegy for representing helth sttus. 11,16 All dimensions of helth were sttisticlly correlted with WAI. This result is consistent with the theoreticl frmework of work bility, which is represented s helth bsed on functionl bility nd presence of diseses, expnded to encompss globl view of helth. 16 Though Rdkiewicz P, Widerszl-Bzyl M. Psychometric properties of Work Ability Index in the light of comprtive survey study. In: Cost G, Goedhrd WJA, Ilmrinen J, editors. Interntionl Congress Series. Proceedings of the 2nd Interntionl Symposium in work bility: ssessment nd promotion of work bility, helth nd well-being of geing workers; 2004 Oct 18-20; Veron, Itly. Amsterdm: Elsevier. 2005; 1280:04-9. b Ilmrinen J, Tuomi K, Seitsmo J. New dimensions of work bility. In: Cost G, Goedhrd WJA, Ilmrinen J, editors. Interntionl Congress Series. Proceedings of the 2nd Interntionl Symposium in work bility: ssessment nd promotion of work bility, helth nd well-being of geing workers; 2004 Oct 18-20; Veron, Itly. Amsterdm: Elsevier. 2005; 1280:-7. c Ilmrinen J. Towrds longer worklife! Ageing nd the qulity of worklife in the Europen Union. Helsinki: Finnish Institute of Occuptionl Helth. Ministry of Socil Affirs nd Helth; p

6 6 Vlidity nd relibility of WAI Mrtinez MC et l significnt, the wek correltions my be justified by the fct tht ech dimension in itself is not cpble of explining the behvior of the overll WAI score, since they re unble to portry the totlity of the helth-disese process. Furthermore, work bility cn be influenced by multifctoril process in which severl elements interct with ech other, often in complex fshion. 6,7 In SF-6, helth dimensions physicl functioning, role-physicl, bodily pin, nd generl helth re representtive of physicl helth, the remining dimensions representing mentl helth. 20 Dimensions of physicl helth were in generl more strongly correlted with WAI thn dimensions of mentl helth. Physicl helth, represented by physicl functioning, is regrded s bsis for work bility given its significnt role in worker impirment, since it reflects the worker s performnce in light of the demnds mde by his or her work. 15, Mentl helth is considered s more relevnt to work in which demnds re predominntly mentl in nture. 15 The criterion vlidity nlysis of the originl instrument showed n ssocition between WAI nd the dopted prmeters. 4 A study of dministrtive workers in Brzil found sttisticlly significnt correltions between work bility nd ll dimensions of helth evluted. 1 In the Europen nurse study, evlution of construct vlidity using self-reported mesures of physicl nd mentl wellbeing showed tht WAI score correlted with self-perceived generl helth sttus, emotionl exhustion, nd disbility. b In the present study, the relibility of the WAI questionnire ws determined using Cronbch s lph coefficient. This pproch yielded coefficient of 0.72, considered s stisfctory. 2 Another WAI relibility study crried out mong Germn workers ged 40 yers or older showed cceptble relibility bsed on test-retest strtegy with four-week intervl between ech dministrtion. 21 The men Cronbch s lph coefficient in the Europen nurse study ws 0.72, indicting stisfctory internl consistency, with the exception of Slovki (0.54), possibly due to bised smpling. b Other Brzilin studies showed Cronbch s lph coefficients for WAI of 0.7 mong dministrtive workers 1 nd 0.90 mong nursing stff. 5 The socio-occuptionl profile of the popultion of the present study differs from tht of the generl popultion in tht our subjects hve higher levels of schooling nd income, re reltively younger, nd perform predominntly physicl nd mentl ctivities. The finl men WAI score ws 41.8 points, indicting high level of work bility, lthough this result is subject to the helthy worker bis. Since this popultion displys very specific chrcteristics in terms of demogrphic profile, helth sttus, nd occuptionl plcement, the psychometric bility of WAI in this context my not be vlid for other Brzilin worker popultions, nd our results should be generlized with cution. From this perspective, WAI relibility should be reevluted prior to ech dministrtion of the instrument. Such precution is imed t identifying vritions in questionnire relibility, which my be ffected by the bredth the of the vrible being mesured, by the chrcteristics of the study popultion, or by the conditions under which mesurement is crried out. 12 One of the limittions of the present study is the definition of cutoff points for the WAI score, which is bsed on results obtined from Finnish workers ged yers, using the following criteri: the 15% of workers with worst scores were considered s with poor bility, the 15% workers with best scores were considered s with excellent bility, nd workers with moderte nd good bility were divided by the medin score. 9,18 Since Brzilin workers hve different demogrphic composition, re exposed to working nd living conditions tht differ from those of Finlnd, nd re likely to be subject to different pttern of functionl geing, the originl cutoff points proposed in the Finnish study my not be vlid, nd were therefore not dopted in the present study. Thus, we recommend tht WAI results be regrded s score until studies imed t vlidting these cutoff points re crried out in the Brzilin setting. Another spect to be considered is tht current WAI ctegories my not be vlid for young workers, since current reference vlues my led to overestimtion of results mong younger subjects. 9 Another ctegoriztion is vilble tht is bsed on Finnish workers in their 0 s; however, follow-up studies will be required to verify the predictive vlue of WAI mong younger workers. 9 WAI results cn be used t both the individul nd collective levels. At the individul level, to identify workers whose functionl cpcity is compromised, so tht support mesures cn be dopted. At the collective level, to trce the generl profile of work bility nd to identify fctors ffecting this profile, so tht corrective inititives my be undertken. 18 Other positive spects of WAI re the ese nd the short time required for its dministrtion, nd its low cost. 18 Ilmrinen J, Tuomi K, Seitsmo J. New dimensions of work bility. In: Cost G, Goedhrd WJA, Ilmrinen J, editors. Interntionl Congress Series. Proceedings of the 2nd Interntionl Symposium in work bility: ssessment nd promotion of work bility, helth nd well-being of geing workers; 2004 Oct 18-20; Veron, Itly. Amsterdm: Elsevier. 2005; 1280:-7. b Rdkiewicz P, Widerszl-Bzyl M. Psychometric properties of Work Ability Index in the light of comprtive survey study. In: Cost G, Goedhrd WJA, Ilmrinen J, editors. Interntionl Congress Series. Proceedings of the 2nd Interntionl Symposium in work bility: ssessment nd promotion of work bility, helth nd well-being of geing workers; 2004 Oct 18-20; Veron, Itly. Amsterdm: Elsevier. 2005; 1280:04-9.

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