Cost and statistical efficiency of posture assessment by inclinometry and observation, exemplified by paper mill work.

Postures at work are paramount in ergonomics. They can be determined using observation and inclinometry in a variety of measurement scenarios that may differ both in costs associated with collecting and processing data, and in efficiency, i.e. the precision of the eventual outcome. The trade-off between cost and efficiency has rarely been addressed in research despite the obvious interest of obtaining precise data at low costs. Median trunk and upper arm inclination were determined for full shifts in 28 paper mill workers using both observation and inclinometry. Costs were estimated using comprehensive cost equations; and efficiency, i.e. the inverted standard deviation of the group mean, was assessed on basis of exposure variance components. Cost and efficiency were estimated in simulations of six sampling scenarios: two for inclinometry (sampling from one or three shifts) and four for observation (one or three observers rating one or three shifts). Each of the six scenarios was evaluated for 1 through 50 workers. Cost-efficiency relationships between the scenarios were intricate. As an example, inclinometry was always more cost-efficient than observation for trunk inclination, except for observation strategies involving only few workers; while for arm inclination, observation by three observers of one shift per worker outperformed inclinometry on three shifts up to a budget of €20000, after which inclinometry prevailed. At a budget of €10000, the best sampling scenario for arm inclination was 2.5 times more efficient than the worst. Arm inclination could be determined with better cost-efficiency than trunk inclination. Our study illustrates that the cost-efficiency of different posture measurement strategies can be assessed and compared using easily accessible diagrams. While the numeric examples in our study are specific to the investigated occupation, exposure variables, and sampling logistics, we believe that inclinometry will, in general, outperform observation. In any specific case, we recommend a thorough analysis, using the comparison procedure proposed in the present study, of feasible strategies for obtaining data, in order to arrive at an informed decision support.

Can home care work be organized to promote health among the workers while maintaining productivity? An investigation into stakeholders' perspectives on organizational work redesign concepts based on the Goldilocks Work principles.

BACKGROUND: Due to the aging population, the need for home care services is increasing in most Western countries, including Norway. However, the highly physical nature of this job could contribute to make recruiting and retaining qualified home care workers (HCWs) challenging. This issue may be overcome by adopting the Goldilocks Work principles, aiming at promoting workers' physical health by determining a "just right" balance between work demands and recovery periods while maintaining productivity. The aim of this study was to 1) gather suggestions from home care employees on suitable organizational (re)design concepts for promoting HCWs' physical health and 2) have researchers and managers define actionable behavioral aims for the HCWs for each proposed (re)design concept and evaluate them in the context of the Goldilocks Work principles. METHODS: HCWs, safety representatives, and operation coordinators (n = 14) from three Norwegian home care units participated in digital workshops led by a researcher. They suggested, ranked, and discussed redesign concepts aimed at promoting HCWs' health. The redesign concepts were subsequently operationalized and evaluated by three researchers and three home care managers. RESULTS: Workshop participants suggested five redesign concepts, namely "operation coordinators should distribute work lists with different occupational physical activity demands more evenly between HCWs", "operation coordinators should distribute transportation modes more evenly between HCWs", "Managers should facilitate correct use of ergonomic aids and techniques", "HCWs should use the stairs instead of the elevator", and "HCWs should participate in home-based exercise training with clients". Only the first two redesign concepts were considered to be aligned with the Goldilocks Work principles. A corresponding behavioral aim for a "just right" workload was defined: reduce inter-individual differences in occupational physical activity throughout a work week. CONCLUSIONS: Operation coordinators could have a key role in health-promoting organizational work redesign based on the Goldilocks Work principles in home care. By reducing the inter-individual differences in occupational physical activity throughout a work week, HCWs' health may be improved, thus reducing absenteeism and increasing the sustainability of home care services. The two suggested redesign concepts should be considered areas for evaluation and adoption in practice by researchers and home care services in similar settings.

Assessing the efficacy of a job rotation for improving occupational physical and psychosocial work environment, musculoskeletal health, social equality, production quality and resilience at a commercial laundromat: protocol for a longitudinal case study.

INTRODUCTION: Job rotation is a work organisation strategy used to reduce work-related exposures and musculoskeletal complaints, yet evidence for the efficacy of the approach is weak. Mismatch between job rotation and company needs, lack of full implementation, lack of exposure variation in included tasks and failure to assess variation may underlie inconclusive research findings to date. The study aims to develop a job rotation with company stakeholders, perform a process evaluation of the implementation, and determine the extent to which the intervention improves the physical and psychosocial work environment, indicators of health, gender and social equality among workers and production quality and resilience. METHODS AND ANALYSIS: Approximately 60 production workers at a Swedish commercial laundromat will be recruited. Physical and psychosocial work environment conditions, health, productivity and gender and social equality will be assessed pre and post intervention, using surveys, accelerometers, heart rate, electromyography and focus groups. A task-based exposure matrix will be constructed, and exposure variation estimated at the level of the individual worker pre and post intervention. An implementation process evaluation will be conducted. Job rotation efficacy will be assessed in terms of improvement in work environment conditions, health, gender and social inequality, and production quality and resilience. This study will provide novel information on the effects of the job rotation on physical and psychosocial work environment conditions, production quality and rate, health and gender and social inequality among blue-collar workers in a highly multicultural workplace. ETHICS AND DISSEMINATION: The study received approval from the Swedish Ethical Review Authority (reference number 2019-00228). The results of the project will be shared directly with the employees, managers and union representatives from the participating company, other relevant labour market stakeholders and with researchers at national and international conferences and via scientific publication. TRIAL REGISTRATION NUMBER: The study is preregistered with the Open Science Framework (https://osf.io/zmdc8/).

Can home care work be organized to promote musculoskeletal health for workers? Study protocol for the Norwegian GoldiCare cluster randomized controlled trial.

BACKGROUND: Home care workers perform physically strenuous tasks, in particular when handling patients with high care demands. Thus, musculoskeletal pain and sick leave is greater in this group than in the general population. To ease these issues, we will implement a Goldilocks Work intervention (GoldiCare), redistributing schedules between workers to achieve a "just right" weekly structure of physical work that can promote health. This protocol paper describes the content, design, implementation and evaluation of the cluster randomized controlled trial of the GoldiCare intervention in home care. METHODS: The cluster randomized controlled trial is a 16-week workplace organizational intervention implemented through operations managers at the home care units. The operations managers will be introduced to the Goldilocks Work Principle and a GoldiCare tool, to assist the operations managers when composing a "just right" distribution of work schedules throughout the week. The GoldiCare tool provides an overview of the physical strain for each shift, based on the number of patients and their need for care. We expect to include 11 units, which will be randomized to either intervention or control at a 1:1 ratio. Home care workers assigned to the control group will continue to work as normal during the intervention period. Musculoskeletal pain in neck/shoulder and lower back will be the primary outcomes and we will also evaluate the composition of physical behaviors as well as fatigue after work as secondary outcomes. We will collect data using (1) daily questions regarding musculoskeletal pain and fatigue after work, (2) 7 days of objective measurements of physical behavior, (3) questionnaires about the participant's characteristics, health, and workplace psychosocial stressors and (4) information on the implementation of the GoldiCare tool. In addition, a process evaluation will be conducted using focus group discussions and individual interviews. DISCUSSION: Due to the increasing aging population in need of care, measures that can improve the health of home care workers are paramount for the sustainability of this sector. This organizational intervention is based on information available nation-wide, and therefore has the potential to be scaled to all municipalities in Norway if proven effective. TRIAL REGISTRATION: This clinical trial was registered on 08/05/2022 under NCT05487027 .

Sitting, standing and moving during work and leisure among male and female office workers of different age: a compositional data analysis.

BACKGROUND: Gendered patterns of physical activity behaviours may help explaining health inequalities between men and women. However, evidence on such patterns in the working population is sparse. This study aimed at documenting and comparing compositions of sitting, standing and moving at work and during leisure among male and female office workers of different age. METHODS: Sitting (including lying), standing and moving were measured using accelerometry for, on average, four working days in 55 male and 57 female Swedish office workers. Behaviours were described in terms of time spent in four exhaustive categories: sitting in short (< 30 min) and long (≥30 min) bouts, standing, and moving. In a compositional data analysis approach, isometric log-ratios (ilr) were calculated for time sitting relative to non-sitting, time in short relative to long sitting bouts, and time in standing relative to moving. Differences between genders (men vs. women), domains (work vs. leisure), and according to age were examined for each ilr using ANOVA. RESULTS: At work, time spent sitting in short bouts, sitting in long bouts, standing, and moving was, on average, 29, 43, 21 and 7% among men, and 28, 38, 26 and 7% among women. Corresponding proportions during leisure were 34, 27, 27 and 13% among men and 28, 27, 32 and 13% among women. Men spent more time sitting relative to non-sitting ([Formula: see text] =0.04, p = 0.03) than women, and less time standing relative to moving ([Formula: see text] =0.07, p = 0.01). At work compared to during leisure, both genders spent more time sitting relative to non-sitting ([Formula: see text] =0.47, p < 0.01); within sitting more time was spent in long relative to short sitting bouts ([Formula: see text] =0.26, p < 0.01), and within non-sitting, more time was spent standing than moving ([Formula: see text] =0.12, p < 0.01). Older workers spent less of their non-sitting time moving than younger workers ([Formula: see text] =0.07, p = 0.01). CONCLUSION: Male office workers spent more time sitting relative to non-sitting than female workers, and more time moving relative to standing. Both genders were sitting more at work than during leisure. Older workers moved less than younger. These workers could likely benefit from interventions to reduce or break up prolonged sitting time, preferably by moving more.

Can childcare work be designed to promote moderate and vigorous physical activity, cardiorespiratory fitness and health? Study protocol for the Goldilocks-childcare randomised controlled trial.

BACKGROUND: Despite extensive efforts, issues like obesity and poor physical capacity remain challenges for a healthy work life in several occupations. The Goldilocks work principle offers a new approach, encouraging design of productive work to promote physical capacity and health. This paper presents the protocol for the Goldilocks-childcare study, a randomised controlled intervention trial aiming to evaluate the effectiveness of implementing the Goldilocks work principle in childcare. The primary aim of the intervention is to increase time in moderate to vigorous physical activity (MVPA) by having the childcare workers act as active role models for children in daily playful physical activities, and thereby improve cardiorespiratory fitness and health of the workers. METHODS: The study is a cluster-randomised trial with a usual-practice wait-list control group. The 10-week intervention consists of two phases. In the first, the childcare workers will participate in two participatory workshops aiming to a) develop playful physical activities ('Goldilocks-games') for children in which childcare workers participate as active role models at MVPA intensity, and b) develop action plans for implementation of the Goldilocks-games in daily work routines. In the second phase, childcare institutions will implement the Goldilocks-games. The primary outcome is working time spent in MVPA, and secondary outcomes are cardiorespiratory fitness, sleeping heart rate, perceived need for recovery, and productivity. Primary outcome and process evaluation will be based on direct measurements of physical activity and heart rate, determination of cardiorespiratory fitness, and questionnaires. DISCUSSION: If proven effective, the Goldilocks work principle has a large potential for promoting sustainable health and working lives of childcare workers. TRIAL REGISTRATION: ISRCTN, ISRCTN15644757, Registered 25th December 2019.

Uncertainty in monetary cost estimates for assessing working postures using inclinometry, observation or self-report.

OBJECTIVE: To assess uncertainty in cost estimates for collecting posture data by inclinometry, observations and self-report. METHOD: In a study addressing physical workloads at a paper mill, costs were calculated for measuring postures of twenty-eight workers during three shifts. Uncertainty in costs was assessed for all three methods as the range between an assumed best case (lowest cost) and worst case (highest cost) using scenario analysis. RESULTS: The cost for observation was larger, but also more uncertain (€16506 and €89552 in the best and worst case, respectively) than that of inclinometry (€7613 - €45896). Self-report costs were both lower and less uncertain (€3743 - €23368). CONCLUSIONS: The extent of uncertainty in cost estimates implies that observation could be less expensive than inclinometry, e.g., in a scenario where experienced observers could use existing software, while inclinometers would have to be purchased. We propose adding uncertainty assessments to cost estimates when selecting a method for measuring working postures, and offer guidance in how to proceed in a specific setting.

Observer variability in posture assessment from video recordings: The effect of partly visible periods.

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 trunk, right upper arm 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.

Musculoskeletal health and work ability in physically demanding occupations: study protocol for a prospective field study on construction and health care workers.

BACKGROUND: Musculoskeletal disorders have a profound impact on individual health, sickness absence and early retirement, particularly in physically demanding occupations. Demographics are changing in the developed countries, towards increasing proportions of senior workers. These senior workers may have particular difficulties coping with physically demanding occupations while maintaining good health. Previous studies investigating the relationship between physical work demands and musculoskeletal disorders are mainly based on self-reported exposures and lack a prospective design. The aim of this paper is to describe the background and methods and discuss challenges for a field study examining physical demands in construction and health care work and their prospective associations with musculoskeletal disorders, work ability and sickness absence. METHODS AND DESIGN: This protocol describes a prospective cohort study on 1200 construction and health care workers. Participants will answer a baseline questionnaire concerning musculoskeletal complaints, general health, psychosocial and organizational factors at work, work demands, work ability and physical activity during leisure. A shorter questionnaire will be answered every 6th months for a total of two years, together with continuous sickness absence monitoring during this period. Analysis will prospectively consider associations between self-reported physical demands and musculoskeletal disorders, work ability and sickness absence. To obtain objective data on physical exposures, technical measurements will be collected from two subgroups of N = 300 (Group A) and N = 160 (Group B) during work and leisure. Both group A and B will be given a physical health examination, be tested for physical capacity and physical activity will be measured for four days. Additionally, muscle activity, ground reaction force, body positions and physical activity will be examined during one workday for Group B. Analysis of associations between objectively measured exposure data and the outcomes described above will be done separately for these subpopulations. DISCUSSION: The field study will at baseline produce objectively measured data on physical demands in the construction and health care occupations. In combination with clinical measurements and questionnaire data during follow-up, this will provide a solid foundation to prospectively investigate relationships between physical demands at work and development of musculoskeletal disorders, work ability and sickness absence.

Cost-efficient assessment of biomechanical exposure in occupational groups, exemplified by posture observation and inclinometry.

OBJECTIVES: This study compared the cost efficiency of observation and inclinometer assessment of trunk and upper-arm inclination in a population of flight baggage handlers, as an illustration of a general procedure for addressing the trade-off between resource consumption and statistical performance in occupational epidemiology. METHODS: Trunk and upper-arm inclination with respect to the line of gravity were assessed for three days on each of 27 airport baggage handlers using simultaneous inclinometer and video recordings. Labor and equipment costs associated with data collection and processing were tracked throughout. Statistical performance was computed from the variance components within and between workers and bias (with inclinometer assumed to produce "correct" inclination angles). The behavior of the trade-off between cost and efficiency with changed sample size, as well as with changed logistics for data collection and processing, was investigated using simulations. RESULTS: At similar total costs, time spent at trunk and arm inclination angles >60 ° as well as 90 (th)percentile arm inclination were estimated at higher precision using inclinometers, while median inclination and 90th percentile trunk inclination was determined more precisely using observation. This hierarchy remained when the study was reproduced in another population, while inclinometry was more cost-efficient than observation for all three posture variables in a scenario where data were already collected and only needed to be processed. CONCLUSIONS: When statistical performance was measured only in terms of precision, inclinometers were more cost-efficient than observation for two out of three posture metrics investigated. Since observations were biased, inclinometers consistently outperformed observation when both bias and precision were included in statistical performance. This general model for assessing cost efficiency may be used for designing exposure assessment strategies with considerations not only of statistical but also cost criteria. The empirical data provide a specific basis for planning assessments of working postures in occupational groups.

Statistical performance of observational work sampling for assessment of categorical exposure variables: a simulation approach illustrated using PATH data.

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 resampling 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 level and task level and for each metric, 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-level 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.

Data processing costs for three posture assessment methods.

BACKGROUND: 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 € 30,630, 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.

Assessment of time patterns of activity and rest in full-shift recordings of trapezius muscle activity - effects of the data processing procedure.

The purpose of this paper was to compare the effects of different data reduction procedures on the values of variables characterizing the time pattern of trapezius muscle activity during full work shifts. Surface electromyography (EMG) of the right and left upper trapezius muscles were obtained from 40 young subjects in different occupations, mainly electricians, hairdressers and students. The target EMG variables were gap frequency, muscle rest, and the number and duration of episodes with sustained muscle activity (from 0.13s to 30min as minimum duration). These variables were derived from the EMG recordings using different Root Mean Square (RMS) windows (from 0.13 to 6.38s), and discrimination levels between "activity" and "rest" (0.5%, 1% and 2% of maximal EMG). The results give basis for practical suggestions for EMG analyses of full work shifts. For most variables, a discrimination level of 0.5% EMGmax showed to be preferable. The time proportion of muscle rest and sustained muscle activity should, in general, be preferred over the corresponding frequency measures. Sustained muscle activity should be calculated using a RMS window between 1 and 3s, and preferably be stated in terms of variables describing time proportions of activity. Uninterrupted activity episodes longer than 10min proved not to be a useful variable due to limited occurrence in many work shifts.

Cost-efficient measurement strategies for posture observations based on video recordings.

Assessment of working postures by observation is a common practice in ergonomics. The present study investigated whether monetary resources invested in a video-based posture observation study should preferably be spent in collecting many video recordings of the work and have them observed once by one observer, or in having multiple observers rate postures repeatedly from fewer videos. The study addressed this question from a practitioner's perspective by focusing two plausible scenarios: documenting the mean exposure of one individual, and of a specific occupational group. Using a data set of observed working postures among hairdressers, empirical values of posture variability, observer variability, and costs for recording and observing one video were entered into equations expressing the total cost of data collection and the information (defined as 1/SD) provided by the resulting estimates of two variables: percentage time with the arm elevated <15° and >90°. Sixteen measurement strategies involving 1-4 observers repeating their posture ratings 1-4 times were examined for budgets up to €2000. For both posture variables and in both the individual and group scenario, the most cost-efficient strategy at any specific budget was to engage 3-4 observers and/or having observer(s) rate postures multiple times each. Between 17% and 34% less information was produced when using the commonly practiced approach of having one observer rate a number of video recordings one time each. We therefore recommend observational posture assessment to be based on video recordings of work, since this allows for multiple observations; and to allocate monetary resources to repeated observations rather than many video recordings.

Efficient assessment of exposure to manual lifting using company data.

The objective of this study, based on an extensive dataset on manual materials handling during scaffolding, was to explore whether routinely collected company data can be used to estimate exposure to manual lifting. The number of manual lifts of scaffold parts while constructing/dismantling scaffolds was well predicted by the number of scaffolders in the team and the type of worksite, in combination with company data of either the number of scaffold parts or the scaffold volume. The proportion of explained variance in the number of lifts ranged from 77% to 92%, depending on the variables in the model. Data on scaffold parts and scaffold volume can easily be obtained from the company's administration, since this is its usual paperwork supporting logistics and customer invoicing, respectively. We conclude that company data can be a promising source of information for ergonomic practitioners and researchers, to support assessment of manual lifting in scaffolding.

Data collection costs in industrial environments for three occupational posture exposure assessment methods.

BACKGROUND: Documentation of posture measurement costs is rare and cost models that do exist are generally naïve. This paper provides a comprehensive cost model for biomechanical exposure assessment in occupational studies, documents the monetary costs of three exposure assessment methods for different stakeholders in data collection, and uses simulations to evaluate the relative importance of cost components. METHODS: Trunk and shoulder posture variables were assessed for 27 aircraft baggage handlers for 3 full shifts each using three methods typical to ergonomic studies: self-report via questionnaire, observation via video film, and full-shift inclinometer registration. The cost model accounted for expenses related to meetings to plan the study, administration, recruitment, equipment, training of data collectors, travel, and onsite data collection. Sensitivity analyses were conducted using simulated study parameters and cost components to investigate the impact on total study cost. RESULTS: Inclinometry was the most expensive method (with a total study cost of € 66,657), followed by observation (€ 55,369) and then self report (€ 36,865). The majority of costs (90%) were borne by researchers. Study design parameters such as sample size, measurement scheduling and spacing, concurrent measurements, location and travel, and equipment acquisition were shown to have wide-ranging impacts on costs. CONCLUSIONS: This study provided a general cost modeling approach that can facilitate decision making and planning of data collection in future studies, as well as investigation into cost efficiency and cost efficient study design. Empirical cost data from a large field study demonstrated the usefulness of the proposed models.

Cost efficiency comparison of four video-based techniques for assessing upper arm postures.

Many video-based techniques for assessing postures at work have been developed. Choosing the most appropriate technique should be based on an evaluation of different alternatives in terms of their ability to produce posture information at low input costs, i.e. their cost efficiency. This study compared four video-based techniques for assessing upper arm postures, using cost and error data from an investigation on hairdressers. Labour costs associated with the posture assessments from the video recordings were the dominant factor in the cost efficiency comparison. Thus, a work sampling technique associated with relatively large errors appeared, in general, to be the most cost-efficient because it was labour-saving. Measurement bias and other costs than labour cost for posture assessment influenced the ranking and economic evaluation of techniques, as did the applied measurement strategy, i.e. the numbers of video recordings and repeated assessments of them. PRACTITIONER SUMMARY: The cost efficiency of four video-based techniques for assessing upper arm postures was compared. Work sampling techniques were in general more cost efficient than continuous observations since they were labour-saving. Whilst a labour cost dominated the comparison, 'hidden costs', bias and measurement strategy also influenced this dominance.

Cost-efficient observation of working postures from video recordings--more videos, more observers or more views per observer?

In ergonomics, assessing the working postures of an individual by observation is a very common practice. The present study investigated whether monetary resources devoted to an observational study should preferably be invested in collecting many video recordings of the work, or in having several observers estimate postures from available videos multiple times. On the basis of a data set of observed working postures among hairdressers, necessary information in terms of posture variability, observer variability, and costs for recording and observing videos was entered into equations providing the total cost of data collection and the precision (informative value) of the resulting estimates of two variables: percentages time with the arm elevated <15 degrees and >90 degrees. In all 160 data collection strategies, differing with respect to the number of video recordings and the number of repeated observations of each recording, were simulated and compared for cost and precision. For both posture variables, the most cost-efficient strategy for a given budget was to engage 4 observers to look at available video recordings, rather than to have one observer look at more recordings. Since the latter strategy is the more common in ergonomics practice, we recommend reconsidering standard practice in observational posture assessment.