The Atlanta Fed writes: Despite a strong impression that entire careers spent with one employer are a thing of the past, some have declared the image of job-hopping millennials a myth. These reports are all based on a September 2014 news release from the U.S. Bureau of Labor Statistics (BLS) stating that among every employee age group (even the youngest), median job tenure has not declined from when it was reported 10 years earlier. (Median job tenure is basically the “middle” amount of job tenure. If all workers are lined up from lowest tenure to highest tenure, the median tenure would be the amount of time the person in the middle of that line has been with his/her employer.)

Chart 1 illustrates the biennial data on job tenure reported by the BLS and interpreted by the reports mentioned above as indication that job tenure is not falling. Each line represents an age range, from 20- to 30-year-olds at the bottom (the lowest median tenure among all age groups) to 61- to 70-year-olds on the top (the age group with the highest median tenure). It sure doesn’t look as though workers at each age group are staying with their jobs for shorter periods.

However, the problem with simply comparing median tenure across time by age group is that different ages at different time periods face different labor market institutions, incentives, and expectations. There are generational, or cohort, differences in what the labor market looks like and has to offer a 25-year-old born in 1923 and a 25-year-old born in 1993. In other words, each generation is represented across the age groups at different points in time.

The different colored points across age groups in chart 1 indicate the range of years the people in that particular year, in that age group, were born (and to what named generation they belong). The labor market facing a 31-to 40-year-old baby boomer in 1996 looks quite different from the labor market facing a 31-to-40-year-old Gen Xer in 2012, and the social, economic, and behavioral differences are even more dramatic the farther apart the generations become.

For example, one of the most dramatic changes facing workers has been the transformation from defined-benefit to defined-contribution retirement plans. The number of years a worker spends with an employer is no longer an investment in the employee’s retirement.

To get a more accurate picture of the lifetime pattern of median job tenure and how it has changed across generations, we use the same BLS data used to produce the chart above to group workers into cohorts, or people who have similar experiences by virtue of when they were born.

What we see in this chart – using the 20- to 30-year-olds, for example – is that the median job tenure was four years among those born in 1953 when they were between 20 and 30 years old. For 20- to 30-year-olds born in 1993 (millennials), however, median job tenure is only one year. Similar – and some even more dramatic – declines occur across cohorts within each age group.