Underwood is founder and principal of The Generational Imperative Inc., Miamisburg, Ohio, and author of the book The Generational Imperative, with over 24 years researching generational dynamics. This report is based on an extensive interview he granted ENR correspondent Judy Schriener in mid-February, 2011.

ENR: What makes demographers start identifying groups of people born in certain years as a “Generation,” such as Gen-X, or Baby Boomer, or Millennial?

UNDERWOOD: New generations begin whenever there’s a significant change in the times they’re going to experience in their youth; in the values they develop. Generations are defined by the core values they’re going to be carrying for a lifetime—but we can’t trust that individuals have embraced generational core values until they’re out of high school.

The year 1982 was a landmark year because teachings, specifically regarding parenting, began to change. They went from a permissive to a protective parenting style. Babies born from then on came of age absorbing different core values.

Millennials go from 1982 to now—with an asterisk. The end date may change later...we can’t tell because generation strategies don’t work until they get to be 18. There’s no such thing as a 15-year-old Millennial or an 8-year-old Millennial.

The so-called First Wave Millennials are now 18 to 29, and Millennials are still pouring into the world. A new generation will begin when we see 18-year-olds with different core values. We have to live in temporary uncertainty for the moment until it shakes out later.

ENR: So what are the Generations in the workforce today?

UNDERWOOD: First Wave Millennials in 2011 are age 18 to 29. About four million a year were born over 12 birth years, so there are about 48 to 50 million of them.

Baby Boomers also were born at a rate of about four million a year, so the Millennials now are almost the same size as the Boomers. Some have inaccurately said the Millennials are bigger than the Baby Boomers but that’s not true.

There are always some immigrants as well. This generation categorization stuff does not apply to immigrants who came in after high school; immigrants have to be dealt with separately.

ENR: Break it down please.

UNDERWOOD: The GI generation, or WWII generation is currently ages 85 and older: 27 birth years � 1901-1926

The Silents, currently 66-84: 19 birth years � 1927-1945

The Baby Boomers, currently 47-65: 19 birth years � 1946-1964

Gen X, currently 30-46: 17 birth years � 1965-1981

First Wave Millennials, currently 18-29:1982 to the present time—with an asterisk.

ENR: Boomers and Gen X appear to dominate the workforce today with Millennials coming on strong. Why should anything change as one generation gradually replaces the other?

UNDERWOOD: X-ers are a population trough. It’s a small generation, born at the rate of about 3.4 million a year.

For every eight boomers there are only six Gen X-ers. For every eight Millennials there are only six X-ers. Gen X will never have known the brutal career competition that Boomers have experienced their entire adult lives and Millennials will experience their entire adult lives.

Gen X is small because:

• 1965, their first birth year, was when the pill first gained widespread use.
• In the 1960s, and thereafter, the women’s movement surged forward and many adult women decided to delay motherhood or forego it in favor of their careers, which for the first time were of significant import.
• In 1973 abortions were legalized. No one knows for sure but there were an estimated one million a year, and that cost that generation probably about eight million members.

Gen X is not inclined to give the world a lot of people leadership, although Gen X almost certainly is going to give America brilliant leadership in terms of new ideas, products, services, processes and systems. Their leadership is going to be in innovation.

That swings the managerial doors wide open for Millennials who focus on their careers. They will probably love the idea of wading into the complexity of people management and people leadership.

Gen X is even smaller than the census numbers might indicate. It was a big immigration era after Viet Nam, and many fit within Gen X’s age bracket—but they don’t share their values.

In terms of the workplace, 59 million Gen X-ers were born in America. Some die off, so there should be fewer than 59 million Gen X-ers but they are counted as more than 60 million because of immigration. With the Millennial birth years the big surge was in Hispanic immigration.

Immigrants have disproportionately migrated to different professions. Hispanics were attracted to construction and manual labor. Middle Easterners are disproportionately attracted to healthcare.

If an immigrant moved to America at age three and their parents encouraged them to embrace American life, today at age 40 that person is almost certainly a member of Gen X. If they came to America at age 16-17, they almost certainly are not a member of Gen X because they do not have the same values.

The questions are, how many of your formative years did you spend in America and did your parents encourage you to embrace American life? That determines if you are in that generation. The first influences...