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Evaluation of alternate category structures for the strain index: an empirical analysis.

Meyers AR; Gerr F; Fethke NB
Hum Factors 2014 Feb; 56(1):131-142
Objective: The purpose fo this study was to develop alternative Strain Index risk classification categories. Background: Strain Index scores are usually categorized into four Strain Index "risk categories." The "original" risk categories were developed in the meat-packing industry and may not be fully applicable to other industries. Method: Daily Strain Index scores were estimated among 276 manufacturing workers participating in a cohort study of occupational risk factors for hand-arm musculoskeletal symptoms. Each score was categorized using the original method and a new method based on quartiles of Strain Index score values among symptomatic participants. Models examining associations between original Strain Index risk categories and incident hand-arm symptoms were compared to models examining associations between the alternative Strain Index risk categories and incident hand-arm symptoms. Results: Compared to the respective referent categories, a twofold or greater increase in the risk of incident hand-arm symptoms was observed for the highest original Strain Index risk category (HR = 2.06, 95% CI = [1.08-3.92]) and for the second highest alternate Strain Index risk exposure category (HR = 2.21, 95% CI = [1.26-3.85]). Although significant associations between Strain Index risk category and incident hand-arm symptoms were observed for both Strain Index categorization methods, model fit statistics favored the alternate approach. Conclusion: Results from this study suggests that the Strain Index risk category structure may need to be tailored to specific populations. Application: If verified, results from this study provide a better way to identify hazardous manufacturing jobs and target them for exposure reduction.
Risk factors; Meat packing industry; Meat handlers; Workers; Work environment; Musculoskeletal system; Musculoskeletal system disorders; Hand injuries; Repetitive work; Models; Statistical analysis; Analytical processes; Exposure levels; Author Keywords: epidemiology; cohort study; ergonomics; musculoskeletal symptoms; Strain Index
Alysha R. Meyers, Industrywide Studies Branch, Division of Surveillance, Hazard Evaluations and Field Studies, National Institute for Occupational Safety and Health, 4676 Columbia Parkway, R-15, Cincinnati, OH 45226
Publication Date
Document Type
Journal Article
Email Address
Funding Type
Grant; Cooperative Agreement
Fiscal Year
Identifying No.
Grant-Number-R36-OH-009486; Grant-Number-R01-OH-007945; B20130801 Grant-Number-T42-OH-008491
Issue of Publication
NIOSH Division
Priority Area
Source Name
Human Factors
Performing Organization
University of Iowa
Page last reviewed: March 3, 2021
Content source: National Institute for Occupational Safety and Health Education and Information Division