(Bloomberg Opinion) — Most of the stereotypes tied to so-called generations are ugly and insulting — whether it’s the greed and materialism associated with “boomers,” the narcissism and entitlement associated with “millennials,” or the aimlessness associated with “Gen X.”Such unpleasantness is not only mean-spirited but also scientifically wrongheaded. The closer researchers look, the more arbitrary they find the boundaries between so-called generations. There’s no evidence that any sorts of personality traits or character flaws go along with so-called boomers, Gen X-ers, millennials or members of Gen Z.You’d think from the seriousness with which people take these things that, rather than continuously producing babies, humans collectively spawn just once every 20 years. Generational labels cropped up just a few days ago in a medical report claiming that millennials are in worse health than were so-called Gen X people at the same age.Around the same time, New York Times columnist Maureen Dowd  generated chatter by writing about her own self-perceived boomer status, using the recent exit of Representative Katie Hill to preach to so-called millennials about the hazards of letting people take nude photos of you. It’s good advice, but it didn’t have to be about generations at all. It could instead be about experience, and hard-won lessons about the ways love sometimes goes rotten.But it’s so much more exciting to invoke generational warfare. People love generation labels in the way they love astrological sign categories — maybe Ms. Hill would still be in office if she’d known not to trust a Scorpio. Some people get deep meaning out of astrology despite a total lack of evidence. Both kinds of labels are social constructs — they affect us only because so many people believe in them.“When you dig into research into differences in discrete generations, there’s no evidence they exist,” says Cort Rudolph, a psychologist at Saint Louis University who has studied age and work-related behavior. “All this generation stuff is total nonsense.”There are two real things that are going on, however. One is that as people age, they go through different stages in life — not quite in lock step, since people reach various maturity levels and adulthood milestones at different times (or not at all). But there’s a progression.And there are events (wars, recessions) and new technologies which may affect those in college or seeking their first jobs differently from those who are older and more established.But those things don’t create generational boundaries. Different studies use different boundaries between the major generations, says Rudolph, making the whole notion of generations into a moving target and therefore not conducive to scientific probing. People roughly classify “boomers” as those between their late 50s and early 70s, Gen X as those in their late 30s to early 50s, and millennials as those in their 20s to late 30s, but this is always shifting, leaving many of us unsure what generation we’re supposed to be in.A few years ago, the U.S. Army funded research into generations to learn how to convince young people to stay in the military. George Washington University psychologist David Costanza, who was involved in that effort, says there was a theory floating around that historical events — such as wars and economic shifts — shaped whole cohorts of people, giving them distinct traits.It’s not that wars, depressions and disease outbreaks such as AIDS don’t shape people — they do. But not, it would seem, in any uniform or predictable way across artificially drawn generational categories. There’s a stereotype that so-called millennials are narcissistic job-hoppers because they have helicopter parents, he says, and that something about the Vietnam War made baby Boomers materialistic.His research suggests that’s all wrong. Millennials are no more narcissistic than anyone else, he says, and not unusually fickle about jobs. A bad economy may force young people to take undesirable first jobs — from which many will hop to something more rewarding when the economy improves. The big misconception, he says, is that merely being in a particular “generation” will endow you with certain traits.Last month, psychologists at UC Santa Barbara published a paper in Science Advances called “Kids These Days: Why Youth of Today Seem Lacking.” They found there’s nothing wrong with kids these days, even though many older people wrongly think younger people have less respect for elders and less love for reading than they themselves had when young.The authors looked into ways to cure these bad assumptions. What they found was that, in the case of reading, if they wrongly told good readers they scored poorly in a test of literary achievement, then suddenly those people got over themselves and they cut younger people more slack.Perhaps younger people, too, might not be so quick to judge so-called boomers if they were not so confident in their own technological proficiency and small carbon footprints. The good news is that with the rise of Gen Z, those who make up these trendy labels will very soon run out of letters. If we’re lucky, that will help put an end to them.To contact the author of this story: Faye Flam at [email protected] contact the editor responsible for this story: Sarah Green Carmichael at [email protected] column does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.Faye Flam is a Bloomberg Opinion columnist. She has written for the Economist, the New York Times, the Washington Post, Psychology Today, Science and other publications. She has a degree in geophysics from the California Institute of Technology.For more articles like this, please visit us at bloomberg.com/opinion©2019 Bloomberg L.P.