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Jackson, J. A. (2017). Bias and Precision in Biomechanical Exposure Assessment: Making the Most of our Methods. (Doctoral dissertation). Uppsala: Acta Universitatis Upsaliensis
Open this publication in new window or tab >>Bias and Precision in Biomechanical Exposure Assessment: Making the Most of our Methods
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Background: Insufficient exposure assessment is a suggested contributing factor to the current lack of clearly characterised relationships between occupational biomechanical risk factors and musculoskeletal disorders. Minimal attention has been paid to the potential bias of measurement tools from expected true values (i.e. accuracy) or between measurement tools, and empirical data on the magnitudes of variance contributed by methodological factors for measurement tool precision are lacking.

Aim: The aim of this thesis was to quantify aspects of bias and precision in three commonly employed biomechanical risk factor assessment tools - inclinometry, observation, and electromyography (EMG) - and provide recommendations guiding their use. Methods: Upper arm elevation angles (UAEAs) were assessed using inclinometers (INC) and by computer-based posture-matching observation, and bias relative to true angles was calculated. Calibration models were developed for INC data, and their efficacy in correcting measurement bias was evaluated. The total variance of trapezius and erector spinae (ES) EMG recordings during cyclic occupational work was partitioned into biological and methodological sources, including the variance uniquely attributable to sub-maximal normalisation. Using algorithms to estimate the precision of a group mean, the efficacy of different trapezius EMG study designs was evaluated. Using precision criteria, the efficacy of different normalisation methods was assessed for ES EMG recordings.

Results and Discussion: Inclinometer measured UAEAs were biased from true angles, with increasing bias at higher angles. In contrast, computer based posture-matching observations were not biased from true angles. Calibration models proved effective at minimizing INC data bias. The dispersion of estimates between- and within- observers at any given set angle underlined the importance of repeated observations when estimating UAEAs. For EMG, a unique but relatively small component of the total variance was attributable to the methodological process of normalisation. Performing three repeats of the trapezius EMG normalisation task proved optimal at minimizing variance for one-day EMG studies, while two repeats sufficed for multi-day EMG studies. A prone normalisation task proved superior for maximizing normalised lumbar ES EMG precision.

Conclusion: Key aspects of measurement tool accuracy, bias between tools, and tool precision were quantified, and recommendations were made to guide future research study design.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. p. 90
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 1329
Keywords
measurement strategy, accuracy, inclinometry, electromyography, EMG, upper arm, shoulder, low back, lumbar, thoracic
National Category
Occupational Health and Environmental Health
Identifiers
urn:nbn:se:hig:diva-23952 (URN)978-91-554-9902-0 (ISBN)
Public defence
2017-06-02, Krusenstjernasalen, Biblioteket, Kungsbäcksvägen 47, Gävle, 13:00 (English)
Opponent
Supervisors
Funder
Forte, Swedish Research Council for Health, Working Life and Welfare, 2009-1761
Available from: 2017-05-23 Created: 2017-05-02 Last updated: 2018-03-13Bibliographically approved
Jackson, J. A., Mathiassen, S. E., Callaghan, J. & Dempsey, P. (2017). Precision based guidelines for sub-maximal normalisation task selection for trunk extensor EMG. Journal of Electromyography & Kinesiology, 37, 41-51
Open this publication in new window or tab >>Precision based guidelines for sub-maximal normalisation task selection for trunk extensor EMG
2017 (English)In: Journal of Electromyography & Kinesiology, ISSN 1050-6411, E-ISSN 1873-5711, Vol. 37, p. 41-51Article in journal (Refereed) Published
Abstract [en]

Aim: The object of this study was to quantify the contribution of sub-maximal normalisation to the overall variance of exposure parameters describing erector spinae (ES) activity, and to provide guidelines for task selection which minimize methodological variance. Methods: ES EMG was measured from three locations (T9, L1 and L5 levels) on fifteen men performing a manual materials handling task in the laboratory on three separate days. Four repeats of each of eleven sub-maximal normalisation tasks (eight static, three dynamic) were collected, work data were normalised to each task and repeat, and exposure parameters calculated. The unique contribution of normalisation to the overall variance was determined for each task and exposure parameter using variance component analyses. Normalisation tasks were scored according to their relative contributions to the overall variance and coefficients of variation.

Results: A prone task, similar to the Biering-Sørensen test posture, was the most repeatable for all electrode locations and across all exposure parameters. Thoracic level normalisation typically showed poorer repeatability than lumbar normalisation.

Discussion: We recommend that future ES EMG studies employing sub-maximal normalisation utilise said prone task. An alternate normalisation task specific to thoracic level ES muscles may be warranted.

Keywords
Exposure variability, variance components, low back, lumbar, erector spinae
National Category
Occupational Health and Environmental Health
Identifiers
urn:nbn:se:hig:diva-23351 (URN)10.1016/j.jelekin.2017.07.001 (DOI)000415646600007 ()28918109 (PubMedID)2-s2.0-85029353680 (Scopus ID)
Funder
Forte, Swedish Research Council for Health, Working Life and Welfare, 2009-1761
Available from: 2017-01-20 Created: 2017-01-20 Last updated: 2018-03-13Bibliographically approved
Wahlström, J., Bergsten, E., Trask, C., Mathiassen, S. E., Jackson, J. & Forsman, M. (2016). Full-shift trunk and upper arm postures and movements among aircraft baggage handlers. Annals of Occupational Hygiene, 60(8), 977-990
Open this publication in new window or tab >>Full-shift trunk and upper arm postures and movements among aircraft baggage handlers
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2016 (English)In: Annals of Occupational Hygiene, ISSN 0003-4878, E-ISSN 1475-3162, Vol. 60, no 8, p. 977-990Article in journal (Refereed) Published
Abstract [en]

Objectives: The present study assessed full shift trunk and upper arm postural exposure amplitudes, frequencies, and durations among Swedish airport baggage handlers, and aimed to determine whether exposures differ between workers at the ramp (loading and unloading aircraft) and baggage sorting areas.

Methods: Trunk and upper arm postures were measured using inclinometers during three full work shifts on each of 27, male baggage handlers working at a large Swedish airport. Sixteen of the baggage handlers worked on the ramp and 11 in the sorting area. Variables summarizing postures and movements were calculated, and mean values and variance components between subjects and within subject (between days) were estimated using restricted maximum likelihood algorithms in a one-way random effect model.

Results: In total, data from 79 full shifts (651 hours) were collected with a mean recording time of 495 minutes per shift (range 319-632). On average, baggage handlers worked with the right and left arm elevated >60° for 6.4% and 6.3% of the total workday, respectively. The 90th percentile trunk forward projection (FP) was 34.1° and the 50th percentile trunk movement velocity was 8°s-1. For most trunk (FP) and upper arm exposure variables, between-subject variability was considerable, suggesting that the flight baggage handlers were not a homogeneously exposed group. A notable between-days variability pointed to the contents of the job differing on different days. Peak exposures (>90°) were higher for ramp workers than for sorting area workers (trunk 0.6% ramp vs 0.3% sorting; right arm 1.3% ramp vs 0.7% sorting).

Conclusions: Trunk and upper arm postures and movements among flight baggage handlers measured by inclinometry were similar to those found in other jobs comprising manual material handling, known to be associated with increased risks for musculoskeletal disorders. The results showed that full-shift trunk (FP), and to some extent peak arm exposures, were higher for ramp workers compared to sorting workers.

Keywords
baggage handling, exposure variability; ergonomics, musculoskeletal disorders, epidemiology
National Category
Occupational Health and Environmental Health
Identifiers
urn:nbn:se:hig:diva-20430 (URN)10.1093/annhyg/mew043 (DOI)000386017300007 ()27417186 (PubMedID)2-s2.0-84990985854 (Scopus ID)
Funder
AFA Insurance, 100071Forte, Swedish Research Council for Health, Working Life and Welfare, 2009-1761
Available from: 2015-10-16 Created: 2015-10-16 Last updated: 2018-03-13Bibliographically approved
Jackson, J. A., Mathiassen, S. E. & Srinivasan, D. (2016). Identification of individual working styles in a long-cycle assembly task using kinematic and EMG variables. In: : . Paper presented at Ninth International Conference on the Prevention of Work-Related Musculoskeletal Disorders (PREMUS), June 20-23, 2016, Toronto, Canada.
Open this publication in new window or tab >>Identification of individual working styles in a long-cycle assembly task using kinematic and EMG variables
2016 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Background.Increased motor variability while performing repetitive tasks has been suggested to decrease the risk of developing musculoskeletal disorders. However, support for this positive effect is lacking outside of short, simple, highly controlled tasks. It is also currently unknown whether or not existing motor variability metrics are viable for characterising occupational tasks. The purpose of this study was to assess motor variability during a long-cycle simulated occupational task. Using metrics previously validated for short-cycle tasks, this study aimed to determine the extent to which: (1) individuals dif-fered in motor variability with respect to kinematics and/or EMG activation; (2) individual motor variability was consistent across days; and (3) kinematics and EMG motor variability were correlated.

Methods.Following a stringent, three-day training regime, 15 females proved sufficiently proficient to participate. On two occasions, participants performed 36 cycles of an assembly task (combining gross and fine motor skills) at 110 MTM pacing (51 s per cycle). For each cycle, multiple upper arm kinematic and trapezius EMG summary mean and SD variables were calculated; for each variable, the variability across the 36 cycles was assessed. The relative size of variability across individuals, and the consistency of each individual’s motor behaviour across days were assessed using kinematic and EMG vari-ables. The correlation between kinematic and EMG variables was also assessed.

Results.Distinct individual behaviours were observed across days: some participants were clearly more consistent in their motor behaviour than others. Further, a high correlation was found between some kinematic and muscle activation variables.

Discussion. Using previously validated upper arm assessment metrics, we were able to differentiate between individuals performing a long-cycle assembly task based on their degree of motor variability. Given the nature of our study task, we believe the metrics that we found to be successful at identifying individual behaviours could be used for assessing field tasks.

Keywords
motor variability, repetitive task, long-cycle assembly, kinematics
National Category
Occupational Health and Environmental Health
Identifiers
urn:nbn:se:hig:diva-21906 (URN)
Conference
Ninth International Conference on the Prevention of Work-Related Musculoskeletal Disorders (PREMUS), June 20-23, 2016, Toronto, Canada
Available from: 2016-06-23 Created: 2016-06-23 Last updated: 2018-12-03Bibliographically approved
Jackson, J. A., Mathiassen, S. E. & Liv, P. (2016). Observer performance in estimating upper arm elevation angles under ideal viewing conditions when assisted by posture matching software. Applied Ergonomics, 55, 208-215
Open this publication in new window or tab >>Observer performance in estimating upper arm elevation angles under ideal viewing conditions when assisted by posture matching software
2016 (English)In: Applied Ergonomics, ISSN 0003-6870, E-ISSN 1872-9126, Vol. 55, p. 208-215Article in journal (Refereed) Published
Abstract [en]

Selecting a suitable body posture measurement method requires performance indices of candidate tools. Such data are lacking for observational assessments made at a high degree of resolution. The aim of this study was to determine the performance (bias and between- and within-observer variance) of novice observers estimating upper arm elevation postures assisted by posture matching software to the nearest degree from still images taken under ideal conditions. Estimates were minimally biased from true angles: the mean error across observers was less than 2°. Variance between observers was minimal. Considerable variance within observers, however, underlined the risk of relying on single observations. Observers were more proficient at estimating 0°and 90° postures, and less proficient at 60°. Thus, under ideal visual conditions observers, on average, proved proficient at high resolution posture estimates; further investigation is required to determine how non-optimal image conditions, as would be expected from occupational data, impact proficiency.

Keywords
measurement error, working postures, observation
National Category
Occupational Health and Environmental Health
Identifiers
urn:nbn:se:hig:diva-19420 (URN)10.1016/j.apergo.2016.01.012 (DOI)000374074600021 ()26995050 (PubMedID)2-s2.0-84959471678 (Scopus ID)
Funder
Forte, Swedish Research Council for Health, Working Life and Welfare, 2009-1761
Available from: 2015-06-01 Created: 2015-06-01 Last updated: 2018-03-13Bibliographically approved
Jackson, J., Mathiassen, S. E., Wahlström, J., Liv, P. & Forsman, M. (2015). Digging deeper into the assessment of upper arm elevation angles using standard inclinometry [Letter to the editor]. Applied Ergonomics, 51, 102-103
Open this publication in new window or tab >>Digging deeper into the assessment of upper arm elevation angles using standard inclinometry
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2015 (English)In: Applied Ergonomics, ISSN 0003-6870, E-ISSN 1872-9126, Vol. 51, p. 102-103Article in journal, Letter (Other academic) Published
Keywords
Validity, Bias, Posture assessment
National Category
Occupational Health and Environmental Health
Identifiers
urn:nbn:se:hig:diva-19344 (URN)10.1016/j.apergo.2015.04.012 (DOI)000358389100012 ()26154209 (PubMedID)2-s2.0-84937416785 (Scopus ID)
Available from: 2015-05-20 Created: 2015-05-20 Last updated: 2018-03-13Bibliographically approved
Jackson, J., Mathiassen, S. E., Wahlström, J., Liv, P. & Forsman, M. (2015). Is what you see what you get? Standard inclinometry of set upper arm elevation angles. Applied Ergonomics, 47, 242-252
Open this publication in new window or tab >>Is what you see what you get? Standard inclinometry of set upper arm elevation angles
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2015 (English)In: Applied Ergonomics, ISSN 0003-6870, E-ISSN 1872-9126, Vol. 47, p. 242-252Article in journal (Refereed) Published
Abstract [en]

Previous research suggests inclinometers (INC) underestimate upper arm elevation. This study was designed to quantify possible bias in occupationally relevant postures, and test whether INC performance could be improved using calibration.

Participants were meticulously positioned in set arm flexion and abduction angles between 0° and 150°. Different subject-specific and group-level regression models comprising linear and quadratic components describing the relationship between set and INC-registered elevation were developed using subsets of data, and validated using additional data.

INC measured arm elevation showed a downward bias, particularly above 60°.  INC data adjusted using the regression models were superior to un-adjusted data; a subject-specific, two-point calibration based on measurements at 0° and 90° gave results closest to the ‘true’ set angles.

Thus, inclinometer measured arm elevation data required calibration to arrive at ‘true’ elevation angles. Calibration to a common measurement scale should be considered when comparing arm elevation data collected using different methods.

Keywords
measurement error, observation, working postures
National Category
Occupational Health and Environmental Health
Identifiers
urn:nbn:se:hig:diva-16159 (URN)10.1016/j.apergo.2014.08.014 (DOI)000347663600028 ()25479994 (PubMedID)2-s2.0-84919663729 (Scopus ID)
Available from: 2014-01-24 Created: 2014-01-24 Last updated: 2018-03-13Bibliographically approved
Mathiassen, S. E., Jackson, J. & Punnett, L. (2014). Statistical performance of observational work sampling for assessment of categorical exposure variables: A simulation approach illustrated using PATH data. Annals of Occupational Hygiene, 58(3), 294-316
Open this publication in new window or tab >>Statistical performance of observational work sampling for assessment of categorical exposure variables: A simulation approach illustrated using PATH data
2014 (English)In: Annals of Occupational Hygiene, ISSN 0003-4878, E-ISSN 1475-3162, Vol. 58, no 3, p. 294-316Article in journal (Refereed) Published
Abstract [en]

Objectives. Observational work sampling is often used in occupational studies to assess categorical biomechanical exposures and occurrence of specific work tasks. The statistical performance of data obtained by work sampling is, however, not well understood, impeding informed measurement strategy design. The purpose of this study was to develop a procedure for assessing the statistical properties of work sampling strategies evaluating categorical exposure variables, and to illustrate the usefulness of this procedure to examine bias and precision of exposure estimates from samples of different sizes.

Methods. From a parent data set of observations on 10 construction workers performing a single operation, the probabilities were determined for each worker of performing four component tasks and working in four mutually exclusive trunk posture categories (neutral, mild flexion, severe flexion, twisted). Using these probabilities, 5000 simulated data sets were created via probability-based re-sampling for each of six sampling strategies, ranging from 300 to 4500 observations. For each strategy, mean exposure and exposure variability metrics were calculated at both the operation- and task-levels and, for each of these, bias and precision were assessed across the 5000 simulations.

Results. Estimates of exposure variability were substantially more uncertain at all sample sizes than estimates of mean exposures and task proportions. Estimates at small sample sizes were also biased. With only 600 samples, proportions of the different tasks and of working with a neutral trunk posture (the most common) were within 10% of the true target value in at least 80% of all the simulated data sets; rarer exposures required at least 1500 samples. For most task-level mean exposure variables and for all operation- and task-level estimates of exposure variability, performance was low, even with 4500 samples. In general, the precision of mean exposure estimates did not depend on the exposure variability between workers.

Conclusions. The suggested probability-based simulation approach proved to be versatile and generally suitable for assessing bias and precision of data collection strategies using work sampling to estimate categorical data. The approach can be used in both real and hypothetical scenarios, in ergonomics as well as in other areas of occupational epidemiology and intervention research. The reported statistical properties associated with sample size are likely widely relevant to studies using work sampling to assess categorical variables.

Keywords
epidemiology, ergonomics, precision, statistical efficiency, working postures
National Category
Occupational Health and Environmental Health
Identifiers
urn:nbn:se:hig:diva-13691 (URN)10.1093/annhyg/met063 (DOI)000333046700004 ()24353010 (PubMedID)2-s2.0-84896338641 (Scopus ID)
Funder
Forte, Swedish Research Council for Health, Working Life and Welfare, 2009-1761
Available from: 2013-01-23 Created: 2013-01-23 Last updated: 2018-03-13Bibliographically approved
Trask, C., Mathiassen, S. E., Jackson, J. & Wahlström, J. (2013). Data processing costs for three posture assessment methods. BMC Medical Research Methodology, 13(1), 124
Open this publication in new window or tab >>Data processing costs for three posture assessment methods
2013 (English)In: BMC Medical Research Methodology, ISSN 1471-2288, E-ISSN 1471-2288, Vol. 13, no 1, p. 124-Article in journal (Refereed) Published
Abstract [en]

Objectives. Data processing contributes a non-trivial proportion to total research costs, but documentation of these costs is rare. This paper employed a priori cost tracking for three posture assessment methods (self-report, observation of video, and inclinometry), developed a model describing the fixed and variable cost components, and simulated additional study scenarios to demonstrate the utility of the model. 

Methods. Trunk and shoulder postures of aircraft baggage handlers were assessed for 80 working days using all three methods. A model was developed to estimate data processing phase costs, including fixed and variable components related to study planning and administration, custom software development, training of analysts, and processing time.   

Results. Observation of video was the most costly data processing method with total cost of 31,433, and was 1.2-fold more costly than inclinometry (€ 26,255), and 2.5-fold more costly than self-reported data (€ 12,491). Simulated scenarios showed altering design strategy could substantially impact processing costs. This was shown for both fixed parameters, such as software development and training costs, and variable parameters, such as the number of work-shift files processed, as well as the sampling frequency for video observation.  When data collection and data processing costs were combined, the cost difference between video and inclinometer methods was reduced to 7%; simulated data showed this difference could be diminished and, even, reversed at larger study sample sizes. Self-report remained substantially less costly under all design strategies, but produced alternate exposure metrics. 

Conclusions. These findings build on the previously published data collection phase cost model by reporting costs for post-collection data processing of the same data set.  Together, these models permit empirically based study planning and identification of cost-efficient study designs.

Keywords
cost-efficiency, shoulder, back, inclinometry, observation, questionnaire, work related musculoskeletal disorders, methods development
National Category
Occupational Health and Environmental Health
Identifiers
urn:nbn:se:hig:diva-13814 (URN)10.1186/1471-2288-13-124 (DOI)000329212500001 ()24118872 (PubMedID)2-s2.0-84885336051 (Scopus ID)
Funder
AFA Insurance, 100071Forte, Swedish Research Council for Health, Working Life and Welfare, Dnr 2009-1761
Available from: 2013-02-09 Created: 2013-02-09 Last updated: 2018-03-13Bibliographically approved
Jackson, J., Banerjee-Guénette, P., Gregory, D. & Callaghan, J. (2013). Should we be more on the ball?: The efficacy of accommodation training on lumbar spine posture, muscle activity, and perceived discomfort during stability ball sitting. Human Factors, 55(6), 1064-1076
Open this publication in new window or tab >>Should we be more on the ball?: The efficacy of accommodation training on lumbar spine posture, muscle activity, and perceived discomfort during stability ball sitting
2013 (English)In: Human Factors, ISSN 0018-7208, E-ISSN 1547-8181, Vol. 55, no 6, p. 1064-1076Article in journal (Refereed) Published
Abstract [en]

Objective: To evaluate the efficacy of a nine-day accommodation protocol on reducing perceived discomfort while sitting on a stability ball (SB); trunk muscle activity levels and lumbar spinal postures were also considered.

Background: Previous studies have compared SB sitting to office chair sitting with few observed differences in muscle activity or posture; however, greater discomfort during SB sitting has been reported.  These findings may indicate an accommodation period is necessary to acclimate to SB sitting.

Methods: Six males and six females completed two separate, two-hour sitting sessions on an SB.  Half the participants completed a nine-day accommodation period between the visits while the other half did not use an SB during the time. On both occasions, self-reported perceived discomfort ratings were collected along with erector spinae and abdominal muscle activity and lumbar spinal postures.

Results: Discomfort ratings were reduced in female participants following the accommodation; no effects on muscle activation or lumbar spine postures were observed.

Conclusion: Accommodation training may reduce perceived low back discomfort in females. Trunk muscle activity and lumbar spine postures during seated office work on an SB did not differ between groups; however, greater sample power was required to conclusively address these variables.

Application: When deciding whether to use an SB in place of a standard office chair, this study indicates females electing to use an SB can decrease discomfort by following an accommodation protocol; no evidence was found to indicate SB chair use will improve trunk strength or posture, even following an accommodation period. 

Keywords
sitting, low back pain, spine biomechanics, office work, ergonomics, chair design, discomfort
National Category
Occupational Health and Environmental Health
Identifiers
urn:nbn:se:hig:diva-13864 (URN)10.1177/0018720813482326 (DOI)000328698000003 ()2-s2.0-84890820056 (Scopus ID)
Available from: 2013-02-20 Created: 2013-02-20 Last updated: 2018-03-13Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-2939-0236

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