Date of Award

January 2016

Document Type


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.


This thesis is restricted to Yale network users only. It will be made publicly available on 05/06/2018