Reliability and validity of self-reported assessment of exposure and outcome variables for manual lifting tasks: a preliminary investigation
Introduction
Lower back injury (LBI) continues to be one of the most common work-related musculoskeletal injuries in any industrialized country. A recent survey revealed that the 12-month period prevalence of LBI was 43% in Hong Kong (Leung et al., 1999). Similarly, NIOSH (1996) reported that back injuries in 1993 accounted for 27% of all non-fatal injuries in the United States (NIOSH, 1996).
Manual lifting has been identified as the physical activity most likely to be associated with LBI (Punnett et al., 1991; Holmström et al., 1992; Knibbe and Friele, 1996). Thus, researchers have focused upon developing models for the assessment of lifting tasks in the workplace (Chaffin and Park, 1973; Chaffin et al., 1978; Ayoub et al., 1983; Liles et al., 1984; Marras et al (1993), Marras et al (1995)). In addition, labour governing bodies have focused on the provision of manual handling guidelines and checklists for the workforce (e.g.: NIOSH, 1981; Victoria Department of Labour, 1988; HSE, 1992; Waters et al., 1993). Despite the efforts from both the labour governing bodies and the scientific arena, lower back injuries statistics have not declined to a satisfactory level. This might be attributed to, among other things, the following: (1) team leaders, work supervisors, and health and safety personnel are not fully aware of the latest development in the scientific arena; and (2) the use of objective methods reported in the published literature may be impractical for workplace assessment because of the time required and equipment involved to fully analyze and interpret lifting tasks.
An alternative approach for the assessment of on manual lifting assessment may be a participatory-based worker methodology. In the past 10 years, participatory ergonomics has emerged as a promising approach that produces positive effects in the workplace (Noro and Imada, 1991; Vink et al., 1995; Brenner and Östberg, 1995; Kuorinka and Patry, 1995). Noro and Imada (1991) suggested that participation recognized the worker as a valuable resource for problem solving. As risk assessment of manual handling tasks is essentially an evaluation of the effects of stress (both physical and non-physical) on the workers, a worker should be the best person to perceive and evaluate the strain effect. Indeed, Burdorf et al. (1997) has commented about the discrete approaches in the identification of multi-factorial nature of work-related lower back disorders and proposed a dynamic model, which incorporated workers as the central theme in the identification of work-related risk factors.
Borg (1982) addressed the use of human perception in evaluating physical exertion and our earlier studies have shown that a linguistic approach in the evaluation of lifting tasks by health and safety professionals as well as industrial workers is consistent with the results in the published literature and that the weight of load is the major determinant of perceived physical effort (PPE) (Genaidy et al., 1999/2000; Yeung et al., 2001). This linguistic approach described lifting variables in words or phrases in a natural language and examined their synergistic effect upon outcome measures.
The study reported herein was conducted to test the use of human knowledge in the evaluation of manual lifting tasks. The specific aims were to document the test–retest reliability of subjects in the evaluation of manual lifting tasks and to validate self-reports with the revised NIOSH lifting equation.
Section snippets
Subjects
Six male and four female physiotherapists with a mean age of 23.3 years and SD of 2.5 years from Hong Kong volunteered to participate in the study. None of them had experienced lower back or musculoskeletal problems in the past 12 months.
Experimental procedures
In the first phase of this study, the participants were asked to assess, using a questionnaire, the effects of lifting variables upon PPE and perceived risk of lifting injury (PRLI) based on their knowledge with the manual lifting of objects. The second phase
Results
The ICC1,1 analysis revealed a mean value of 0.62 across all lifting conditions (Table 1). The weight of load showed a higher reliability for “heavy” load (ICC1,1=0.76) than “moderate” (ICC1,1=0.65) and “low” levels (ICC1,1=0.46). In general, the reliability was higher for high levels of lifting parameters (i.e. “heavy”, “far” and “long”).
The relationship between PPE and PRLI was subjected to first-, second- and third-order polynomial regression analyses. Results indicated that the third-order
Discussion
Traditionally, researchers have focused on the reliability of self-reported working postures, weight of load, and frequency of work activities. For example, Hammarskjöld et al. (1989) evaluated the reproducibility of three commonly used working postures among carpenters. They showed a 10% coefficient of variation between trials. Furthermore, Gamberale et al. (1987) showed a high test–retest reliability of the workers in the selection of weight (r=0.77) and pace (r=0.91) in the determination of
Conclusions
The results of this study suggest a moderate to high test–retest reliability of human expertise in the evaluation of manual lifting tasks. The reliability improved for higher levels of physical effort. The general agreement between the subjects’ evaluation and NIOSH LI provides preliminary indications that human-based methodologies may be further explored on experienced workers.
Acknowledgements
The work described in this paper was partially supported by a grant from the Hong Kong Occupational Safety and Health Council (Research Grant No. 98001). Special thanks to Mr. Wong Man Hung for his assistance in the data collection.
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