Date of Award


Document Type

Open Access Thesis

Degree Name

Master of Public Health (MPH)


School of Public Health

First Advisor

Martin D. Slade


Objective: This study aimed to investigate the effect of union status on risk of injury among a cohort of aluminum manufacturing workers.

Methods: This cohort study included all hourly employees at 19 U.S. plants, which were in operation between 2000 and 2007. Workers were classified into unionized and non-unionized groups. The final dataset combined a human resources database, which includes information about job history and socio-demographic information, and an incident management system, which includes information on work-related injuries. Injuries were classified by severity into four mutually exclusive categories: injuries requiring first aid, medical treatment, work restriction, and lost work time. Descriptive statistics using Chi-square and student’s t-test were calculated. Survival curves and cox-proportional hazard models were used to determine the outcome, which was the individual’s time to first injury within a standardized job category.

Results: A total of 27,600 hourly workers included; 19,115 (71%) were unionized while 8,485 (29%) were non-unionized. The cohort of 27,600 persons contributed a total of 41,522 person-jobs (30,360 unionized vs. 11,162 non-unionized). Looking at first injury of any type, union person-jobs incurred 9,290 injuries (30% of union person-jobs) compared to 2,599 injuries in non-union person-jobs (23% of non-union person-jobs). A similar relationship was observed when considering only first OSHA recordable injuries. After adjusting for multiple covariates, union workers had a 27% higher risk of early injury of any type and a 34% higher risk of earlier first recordable injury compared to non-union workers.

Conclusion: Our results provide evidence associating union status with higher risk of earlier injuries, whether these injuries were OSHA recordable or first aid only.

Open Access

This Article is Open Access