People who hold down more than one job not only experience an increased risk of injury at work, but while they’re not at work as well, according to a new study.

Published in the January issue of the American Journal of Public Health, the study found that multiple job holders had a “significantly” higher injury rate per 100 workers for work- and nonwork-related injuries when compared to single job holders. The study, which was based on 1997-2011 data from the National Health Interview Survey, examined nearly 7,500 injury episodes reported during the 15-year study period, of which 802 were reported by multiple job holders and about 2,250 were work-related. When weighted, it comes to about 4.5 million work-related injuries each year, of which about half a million are among multiple job holders. Researchers concluded that even after adjusting for the additional hours worked, multiple job holders still face a higher risk of injury.

The study noted that the effects of working multiple jobs has attracted little attention from researchers and is often overlooked within public health and injury surveillance systems. Much occupational injury research focuses on a person’s primary employment. But in 2011, about 5 percent of U.S. workers reported working more than one job within the same week, while some estimates put the number of men working multiple jobs as high as 20 percent. Authors Helen Marucci-Wellman, Joanna Willetts, Tin-Chi Lin, Melanye Brennan and Santosh Verma write:

Injury research and standard surveillance systems have disregarded multiple job holding, instead describing injury morbidity in terms of exposures at the primary job or the job in which the worker was working when injured. Furthermore, most of the current injury surveillance systems and standard employment surveys in the United States do not account for the dynamic fluctuations in work forms present today.

Researchers found that multiple job holders wore more likely to be college educated, younger, white, nonmarried, working 50 or more hours each week, employed in the service sector, and with less tenure at their primary job. The higher rate of work injuries among multiple job holders was statistically significant among women, those with some college education, workers ages 25 to 44, and whites.

Female multiple job holders, who are more likely than men to have multiple part-time jobs, experienced more work injuries than single job holders. The authors noted that “female part-time workers are usually paid hourly, receive lower wages, and have unstable and unpredictable hours, potentially increasing risk.” The study also found elevated work injury rates among young and blue-collar multiple job holders (though injuries among blue-collar occupations are already the highest of any category).

An obvious explanation for the higher risk among multiple job holders is fatigue, but the researchers said that doesn’t fully explain the numbers. Other factors could be trying to fit full-time workloads into part-time hours, worker inexperience with the job at hand, or less employer investment in part-time workers. In regard to multiple job holders’ increased risk of injury while not at work, study authors said it may be associated with fatigue or the “potentially hectic structure” of working two jobs.

The authors described their findings as a “conservative” estimate of the injury risk to multiple job holders, and noted that the study is limited by low reporting of work injuries among blacks and Hispanics.

To request a full copy of the study, click here.

Kim Krisberg is a freelance public health writer living in Austin, Texas, and has been writing about public health for more than a decade.

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