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  • 1.
    Garza, Jennifer
    et al.
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, Occupational health science. University of Gävle, Centre for Musculoskeletal Research.
    Mathiassen, Svend Erik
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, Occupational health science. University of Gävle, Centre for Musculoskeletal Research.
    Heiden, Marina
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, Occupational health science. University of Gävle, Centre for Musculoskeletal Research.
    Reliability of using observations when assessing different posture variables2016Conference paper (Refereed)
    Abstract [en]

    Background. Working in extreme postures has been identified as a risk factor for musculoskeletal symptoms. Directly measuring work postures is considered to be the most accurate approach for assessing these exposures, but it is often not feasible to directly measure posture due to time or budget constraints. Alternatively, direct measurements of postures can be predicted based on observations of workers’ postures. Since observers are known to differ in posture ratings, it may, however, be necessary to develop calibration procedures for each specific observer.

    Methods. Arm and back postures of a random sample of 28 paper mill workers were measured via inclinometry and also were assessed by three observers from videos. Linear models with participant number and observer as random effects were resolved to assess whether or not observed postures were associated with the corresponding inclinometer values and if the effect of observer on slope and intercept was significant (p<0.05). The variance explained by these models was compared to the variance explained by corresponding linear models yet with observer entered as a fixed effect (i.e. allowing different slopes and intercepts for different observers).

    Results. For all postures, the variance explained was similar when using observer as a fixed compared to a random effect (R-squared ranging from 0.41 to 0.56 for observer as fixed or random effect). Throughout, participant was the major source of variance.

    Discussion. Our findings of similar amounts of variance explained when using observer as a fixed compared to a random effect for all postures indicates that calibration models developed for each individual observer may not necessarily perform better than a general calibration applying to any observer. Since posture observations explained only a small proportion of directly measured posture variance, observation may not be very useful in this setting

  • 2.
    Heiden, Marina
    et al.
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, Occupational health science. University of Gävle, Centre for Musculoskeletal Research.
    Garza, Jennifer
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, Occupational health science. University of Gävle, Centre for Musculoskeletal Research.
    Trask, Catherine
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, Occupational health science. University of Gävle, Centre for Musculoskeletal Research.
    Mathiassen, Svend Erik
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, Occupational health science. University of Gävle, Centre for Musculoskeletal Research.
    Cost-efficient assessment of variation in arm posture during paper mill work2016Conference paper (Refereed)
    Abstract [en]

    Background. Arm posture is a recognized risk factor for occupational upper extremity musculoskeletal disorders and thus often assessed in research and practice. Posture assessment methods differ in cost, feasibility and, perhaps, bias. An attractive approach could be to build statistical models for predicting results of expensive direct measurements of arm posture from cheaper or more accessible data, and apply them to large samples in which only the latter data are available. We aimed to build and assess the performance of such prediction models in a random sample of paper mill workers.

    Methods. 28 workers were recruited to the study, and their upper arm postures were measured during three full work shifts using inclinometers. Simultaneously, the workers were video filmed, and their arm posture and gross body posture were assessed by observing the video afterwards. Models for predicting the inclinometer-assessed duration (proportion of time) and frequency (number/min) of periods spent in neutral right arm posture (<20°) were fitted using subject and observer as random factors, measured shift (1, 2 or 3) as fixed factor, and either observed time in neutral right arm angle or observed gross body posture as predictor.

    Results. For the proportion of time spent in neutral arm posture, the best performance was achieved by using observed gross body posture as predictor (explained variance: R2=26%; standard error: SE=9.8). For the frequency of periods spent in neutral arm posture, the corresponding model fit was R2=60% and SE=5.6. Bootstrap resample validation of the latter model showed an expected performance in other samples of R2=59-60% and SE=5.5-5.6 (5th-95th percentile).

    Discussion. Surprisingly, we found that observed gross body posture was a better predictor of variation in arm posture than observed arm angles. The findings suggest that arm posture during paper mill work can be cost-efficiently assessed using simple observations.

  • 3.
    Heiden, Marina
    et al.
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, Occupational health science. University of Gävle, Centre for Musculoskeletal Research.
    Garza, Jennifer
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, Occupational health science. University of Gävle, Centre for Musculoskeletal Research. Division of Occupational and Environmental Medicine, University of Connecticut Health Center, Farmington, USA.
    Trask, Catherine
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, Occupational health science. University of Gävle, Centre for Musculoskeletal Research. Canadian Centre for Health and Safety in Agriculture, College of Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
    Mathiassen, Svend Erik
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, Occupational health science. University of Gävle, Centre for Musculoskeletal Research.
    Predicting directly measured trunk and upper arm postures in paper mill work from administrative data, workers’ ratings and posture observations2017In: Annals of Work Exposures & Health, ISSN 2398-7308, Vol. 61, no 2, p. 207-217Article in journal (Refereed)
    Abstract [en]

    Introduction: A cost-efficient alternative to measuring working postures directly could be to build statistical models for predicting results of such measurements from cheaper data, and apply these models to samples in which only the latter data are available. The present study aimed to build and assess the performance of statistical models predicting inclinometer-assessed trunk and arm posture among paper mill workers. Separate models were built using administrative data, workers’ ratings of their exposure, and observations of the work from video recordings as predictors.

    Methods: Trunk and upper arm postures were measured using inclinometry on 28 paper mill workers during three work shifts each. Simultaneously, the workers were video filmed, and their postures were assessed by observation of the videos afterwards. Workers’ ratings of exposure, and administrative data on staff and production during the shifts were also collected. Linear mixed models were fitted for predicting inclinometer-assessed exposure variables (median trunk and upper arm angle, proportion of time with neutral trunk and upper arm posture, and frequency of periods in neutral trunk and upper arm inclination) from administrative data, workers’ ratings, and observations, respectively. Performance was evaluated in terms of Akaike information criterion, proportion of variance explained (R2), and standard error of the model estimate (SE). For models performing well, validity was assessed by bootstrap resampling.

    Results: Models based on administrative data performed poorly (R2≤15%) and would not be useful for assessing posture in this population. Models using workers’ ratings of exposure performed slightly better (8%≤R2≤27% for trunk posture; 14%≤R2≤36% for arm posture). The best model was obtained when using observational data for predicting frequency of periods with neutral arm inclination. It explained 56% of the variance in the postural exposure, and its SE was 5.6. Bootstrap validation of this model showed similar expected performance in other samples (5th-95th percentile: R2=45-63%; SE=5.1-6.2).

    Conclusions: Observational data had a better ability to predict inclinometer-assessed upper arm exposures than workers’ ratings or administrative data, but they are typically more expensive to obtain. The results encourage comparisons of the cost-efficiency of modeling based on administrative data, workers’ ratings, and observation.

  • 4.
    Heiden, Marina
    et al.
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, Occupational health science. University of Gävle, Centre for Musculoskeletal Research.
    Mathiassen, Svend Erik
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, Occupational health science. University of Gävle, Centre for Musculoskeletal Research.
    Prediction of trunk and upper arm postures in paper mill workers by statistical modelling: an empirical validation study2015In: Proceedings of the 19th Triennial Congress of the International Ergonomics Association, Melbourne 9-14 August 2015 / [ed] Gitte Lindgaard & Dave Moore, 2015Conference paper (Refereed)
  • 5.
    Trask, Catherine
    et al.
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, Occupational health science. University of Gävle, Centre for Musculoskeletal Research. Centre for Health and Safety in Agriculture, College of Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
    Mathiassen, Svend Erik
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, Occupational health science. University of Gävle, Centre for Musculoskeletal Research.
    Rostami, Mehdi
    Collaborative Biostatistics Program, School of Public Health, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
    Heiden, Marina
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, Occupational health science. University of Gävle, Centre for Musculoskeletal Research.
    Observer variability in posture assessment from video recordings: the effect of partly visible periods2017In: Applied Ergonomics, ISSN 0003-6870, E-ISSN 1872-9126, Vol. 60, p. 275-281Article in journal (Refereed)
    Abstract [en]

    Observers rank partly visible postures on video frames differently than fully visible postures, but it’s not clear if this is due to differences in observer perception. This study investigated the effect of posture visibility on between-observer variability in assessments of trunk and arm posture.  Trained observers assessed trunk and arm postures from video recordings of 84 pulp mill shifts using a work sampling approach; postures were also categorized as ‘fully’ or ‘partly’ visible.  Between-worker, between-day, and between-observer variance components and corresponding confidence intervals were calculated. Although no consistent gradient was seen for the right upper arm, trunk posture showed smaller between-observer variance when all observers rated a posture as fully visible. This suggests that, partly- visible data, especially when observers disagree as to the level of visibility, introduces more between-observer variability when compared to fully visible data.  Some previously-identified differences in daily posture summaries may be related to this phenomenon.

  • 6.
    Trask, Catherine
    et al.
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, Occupational health science. University of Gävle, Centre for Musculoskeletal Research.
    Mathiassen, Svend Erik
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, Occupational health science. University of Gävle, Centre for Musculoskeletal Research.
    Rostami, Mehdi
    Collaborative Biostatistics Program, School of Public Health, University of Saskatchewan.
    Heiden, Marina
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, Occupational health science. University of Gävle, Centre for Musculoskeletal Research.
    Variance components of observed postural exposure - the effect of partly visible periods2016Conference paper (Refereed)
    Abstract [en]

    Background. Previous studies have shown that video-based observation of postures that are only partly visible leads to different daily summary values than when postures are fully visible. However, the source of these differences is unclear. The purpose of this study was to estimate the between-observer variance of trunk and arm posture estimates (relative to within- and between-worker variance), and to investigate the effect of visibility on this observer variability of trunk and arm postural exposure estimates.

    Methods. Video recordings were made of 28 pulp mill workers for three full shifts each. Trunk and arm postures were then estimated by trained observers using a work sampling approach; posture images were also assessed as being “fully” or “partly” visible. REML techniques were used to estimate the between-worker, between-day and betweenobserver components of variance at different visibility levels; Wald-based confidence intervals and p-values were used to determine sources of variation.

    Results. Estimates of partly visible postures (as agreed upon by all observers) were lower than fully visible postures. However, more than 90% of trunk observations and 85% of arm observations did not have full agreement on visibility between observers. Right upper arm posture showed smaller between-observer variance when all observers rated a posture to be fully visible, as compared to all observers agreeing it was only partly visible. This suggests partly visible data introduces more methodological (i.e. between-observer) variability when compared to fully visible data. However, no significant differences in between-observer variability were found for the trunk, suggesting that other factors explain the reported differences in estimated postures between fully and partly visible data in this case.

    Discussion. Future studies involving concurrent direct measurement would determine whether there is a true difference in posture between partly visible and fully visible periods, or whether the difference between fully and partly visible periods are related to observer performance.

1 - 6 of 6
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