Here's what millions of Americans fear most about their jobs

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American workers believe the forces of globalization are the biggest threat to their paychecks, but they're much less worried about the impact of immigration on job security.

Those are among the findings of a comprehensive study of changing attitudes in the modern workplace and the forces that have brought dramatic changes to the working lives of Americans.

The study, released Thursday by the Pew Research Center and the Markle Foundation, is based on decades of government data and survey results with some 5,000 Americans.

The results show an increasing demand for more highly skilled workers, a trend that many workers say will require them to continue their education and training throughout their careers. And the majority of those surveyed said the responsibility for getting that training lies with individual workers — more than government, employers or schools.

Attitudes about the impact of globalization were mixed. While the study found that workers most fear outsourcing of work to foreign countries, they also believe boosting exports of U.S. goods helps American workers.

The survey respondents said that other major threats to U.S. workers included greater reliance on contract and temporary work and the decline in union membership.

But Americans are less worried about the impact of immigration today on their jobs than they were a decade ago, the survey found.

Opinion is about evenly divided on whether the growing number of immigrants working in the U.S. helps or hurts workers, a marked shift from 2006, when immigration was seen as harmful by a nearly two-to-one margin.

No matter which forces they see as threats to their paychecks, most Americans see education and training as the key to job security and career success.

While 39 percent of those without a high school education said they were very or fairly likely to be laid off in the next 12 months, only 7 percent of those with a bachelor's degree or more feared losing their jobs. Those with lower levels of education also said they didn't have the skills to advance in their career or find a good job locally.

While most agreed that education is important, they were divided on the value of a traditional college degree.

Many college graduates said their education had a positive impact on their personal and professional development, but just 16 percent of all Americans think that a four-year degree prepares students "very well" for a nicely paying job in today's economy.

The study also highlighted some major shifts in the makeup of the workforce and the impact on the American workplace.

While the overall employment rate is about the same as it was in 1980, the average age has increased as younger workers make up a much smaller share of working Americans and older workers are staying on the job longer and later in life.

Less than half of those aged 16 to 24 were working last year, compared with 57 percent in 2000. The Pew researchers noted that's partly because more young adults are enrolled in college than they were in 1980. At the same time, the share of adults 65 and older who are still working has risen from 12 percent in 1980 to 19 percent in 2015.

Despite worries about job security, workers are staying with the same employer for longer before moving on to a new job or retiring. That's due in part to the increased share of older workers, who tend to stay in a job longer. The Great Recession may also have made it harder for workers of all ages to switch jobs, the researchers said.

Americans are also putting in more time at work than they have in decades.

While incomes have recently begun rising again after a long flat spell, the median household income is about where it was 15 years ago. But it takes more hours to generate that income.

Since 1980, American workers are putting in an average of nearly four more weeks of work each year — from 43 weeks in 1980 to 46.8 weeks in 2015. The average length of a typical workweek is also up, rising to 38.7 hours in 2015 from 38.1 hours in 1980.21.

That means the average worker is putting in about an extra month's worth of work compared to 1980.

Most of those extra hours came from the large number of women who entered the workforce over the last four decades. Women increased their average workweek from 34.1 hours in 1980 to 36.2 hours last year, while the average for men was unchanged at about 41 hours.

Older workers also boosted the average hours worked. Workers 65 and older boosted their time on the job from 29.3 hours a week in 1980 to 33.7 in 2015. They also raised the number of weeks worked a year from 38.3 to 44.6.