Cohort Shift
When reflecting on our own lives, especially on our college years, many of us can recall unusual cohort-groups coming of age as young adults—perhaps a few years younger, perhaps a few years older than ourselves. In the memory of the living, this has happened four times. In the early 1920s, an upbeat, collectivist batch replaced the cynics and individualists. In the late 1940s, a suddenly risk-averse batch replaced the can-do war heroes. In the mid-1960s, a fiery batch replaced the adult emulators. 
And around 1980, a smooth and knowing batch replaced the complainers. Whichever side of the line they were on, college alumni commonly remember these breakpoints. Others can recall less dramatic shifts: the rising drug use among successive college freshmen cohorts in the late 1960s and early 1970s, for example, or the growing popularity of military and entrepreneurial careers among those who came to campus in the early 1980s. As you grow older, you look at other age groups and wonder whether you are changing or they are changing. The answer, quite often, is neither: You were both different to begin with. You were born at different times. You belong to different cohort-groups.
What exactly does it mean to belong to a cohort-group? Unlike many group definitions (like neighborhood or career), cohort-group membership is involuntary. Then again, so is age. But unlike age, cohort-group membership is permanent. And unlike sex or race (also involuntary and permanent), it applies to a finite number of identifiable individuals. After its last birth-year, a cohort-group can only shrink in size. Fixed in history, it must eventually disappear. What makes the cohort-group truly unique is that all its members—from birth on—always encounter the same social events and moods and trends at similar ages. They retain, in other words, a common age location in history throughout their lives. Since history affects people very differently according to their age, common age location is what gives each cohort-group a distinct biography and a distinct lifecycle.
We have no trouble appreciating age location when thinking of momentous historical events like war, depression, revolution, or spiritual prophecy. These events obviously impress people differently at different ages. The same cataclysm that a 10-year-old finds terrifying, a 30-year-old may find empowering, a 50-year-old calming, a 70-year-old inspiring. Once received, such impressions continue to shape the personality people take with them as they grow older. Today’s ninetyish elders, for instance, came of age with the New Deal, World War II, and collective heroism. Even in late elderhood, they retain their taste for teamwork—and often wonder why self-obsessed “yuppies” never had it. 
Their fiftyish juniors, on the other hand, came of age with Vietnam, Watergate hearings, and “Consciousness III” euphoria. They retain their taste for introspection, and often wonder why bustling “senior citizens” never had it. The 90-year-old had no Woodstock, the 50-year-old no D-Day—nothing even close. This coming-of-age contrast will continue to influence both groups’ attitudes toward the world—and toward each other—for as long as they live. Likewise, a very different contrast will always separate those who were children at the time of D-Day and Woodstock. If D-Day empowered young-adult G.I.s, it intimidated Silent children. And if Woodstock brought inner rapture to 25-year-old Boomers, it made 5-year-old Xers feel that the adult world was turning hysterical.
Age location also shapes cohort-groups through historical shifts in society-wide attitudes toward families, schooling, sex-roles, religion, crime, careers, and personal risk. At various moments in history, Americans have chosen to be more protective of children, or more generous to old people, or more tolerant of unconventional young adults. Then, after a while, the mood has swung the other way. Each time this happened, the social environment changed differently for each cohort-group. 
Take “open classrooms” in the early 1970s; or A-bomb drills for elementary students in the mid-1950s; or the huge rise in Social Security benefits in the mid-1970s. All were passing fads, but fads that forever changed the lives of the specific cohort-groups affected by them. The first permanently if subtly altered how today’s 40-year-olds feel about parental authority; the second, how today’s 55-year-olds feel about nuclear deterrence; the third, how today’s 90-year-olds feel about their social status relative to their next-juniors. Trees planted in the same year contain rings that indicate when they all met with the cold winter, wet spring, or dry summer. Cohort-groups are like trees in this respect. They carry within them a unique signature of history’s bygone moments.
Almost by design, America’s present-day social institutions accentuate the power of age location. The more tightly age-bracketed the social experience, the more pronounced the ultimate cohort identity. From kindergarten through high school, almost all pupils in any one classroom belong to the same birthyear. In nonschool activities like Little League and scouting, children participate within two- or three-year cohort-groups. College-age students date, study, and compete athletically within cohort-groups seldom exceeding five years in length. As modern adults age into midlife, their friendships typically widen into longer birthyear zones. But their cohort bonds remain strong. Most retain contact with circles of like-aged friends, with (or against) whom they measure progress at each phase of life. High school and college reunions remind alumni of their cohort bonds—how each class remains, in important respects, different from those a few years younger or older. Over the last few decades, cohorts have even been “retiring” together in their early to mid-sixties. Like all status designations (including sex, race, or profession), cohort-group membership forges a sense of collective identity and reinforces a common personality.
Quantitative research on cohorts is still a young science. The very term “birth cohort” was not coined until 1863 (by the French sociologist Émile Littré), and the concept attracted little attention over the next hundred years. Since the early 1960s, the interest has grown more serious—especially in America. Intrigued by lifecycle shifts, a few historians have begun to pore over town archives, gravestones, and census records to study cohort-groups in small communities. Social scientists have also begun to look more carefully at modern behavioral data from a birthyear perspective. All this could not happen at once. The number crunchers first had to wait until they could obtain age-bracketed data for the American population at large. Then they had to wait still longer until time could sort out the independent effect of cohort membership from other behavior-shaping variables such as phase of life (the “age effect”) and historical change (the “period effect”). But as the widespread collection of age-bracketed data enters its fourth decade, the results are finally arriving. More often than not, they show that cohorts matter a great deal.
Survey analysis of voting behavior is a classic case in point. In the early 1960s, researchers discovered that Americans age 65 to 80 voted heavily Republican, while younger Americans voted Democratic. At that time, three explanations seemed equally plausible: People always tend to vote Republican when they get old (the age effect); elders were the leading wave of a national trend toward Republicanism (the period effect); or the 1890s cohort-group leans Republican (the cohort effect). Most experts opted for the first answer—the age effect. “Aging seems to produce a shift toward Republicanism,” concluded one study in 1962. “The pattern appears to be linear.” Wrong. Two decades have passed, and survey researchers have been able to isolate and measure the influence of each effect. Cohorts win, hands down. The post-1970 arrival of a new and increasingly Democratic batch of 65-to-80-year-olds made cohorts the only possible explanation. So, a decade later, did the arrival of a new and increasingly Republican batch of 18-to-28-year-olds.
Further confirmation of the power of cohorts comes from longitudinal tests of intelligence and educational aptitude. For a third of a century, psychologist K. Warner Schaie has measured the “psychometric intelligence” of 7-year cohort-groups—born from 1886 through 1962—living in Seattle, Washington. Schaie’s original purpose was to trace universal lifecycle trends (the age effect) in aptitude scores. In this, he has been successful. His surveys show that measured intelligence rises most steeply in the twenties, begins to level off during the thirties, and enters a gradual decline after the early fifties. 
What Schaie was not looking for—but found—was a powerful correlation between his aptitude scores and his specific cohort-groups. In each case, the cohort effect remained strong even after Schaie isolated it both from the influence of age and from the influence of historical changes such as better schooling. In fact, among subjects under age 70, most measures of aptitude vary far more across cohort lines than across age brackets. (See sidebar.)
Such marked contrasts between cohort-groups prompt us to ask searching questions about the age location and collective biography of each group. As yet, however, research on cohort effects remains in its infancy, and seldom are such questions ever addressed. Even when birthyear information is available, most experts do not bother to isolate it from data presented under other labels. A typical table shows age on the vertical axis, calendar year on the horizontal. Thus, by implication (though not by label) the cohort lies along the generational diagonal. Unless you are looking “diagonally” for the cohort effect, you will not see it. And unless you are willing to wait many years, you cannot rule out that what you see is simply due to aging or to historical trends affecting all age brackets.
Reading along the generational diagonal shows us that history does not always move in a straight line. It also prompts us to ask why. What differences in parental nurture, schooling, adult expectations, economic trends, or cultural tone might explain why the early-1960s cohorts scored so low on aptitude tests? Or why the early-1920s cohort (if Seattlans are any guide) grew up scoring so high? The closer we look, the more interesting such questions become. Why, for example, did the schoolchildren of the 1930s develop such strong number skills, and then raise their own children (the Jack-and-Jill readers of the 1950s) to have such a commanding grasp of verbal meaning? What was it about the nurture of that 1885-1900 cohort-group that produced such precocious talent at “word play”—culminating in memorable slang, brilliant mystery fiction, the invention of crossword puzzles, five of America’s seven Nobel Prizes for literature, and the greatest elder elocutionists (from Adlai Stevenson to Claude Pepper) of the 20th century?
Countless such questions lie unanswered among the myriad cohort-groups of the past four centuries. How and at what age did history shape them? And how and at what age did they in turn shape history? (See sidebar.)
