Age Stratification & Cohort Flow: Definitions & Theories

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  • 0:01 Age
  • 0:57 Age Stratification
  • 2:51 Cohort Flow
  • 5:06 Lesson Summary
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Lesson Transcript
Instructor: Christopher Muscato

Chris has a master's degree in history and teaches at the University of Northern Colorado.

Age matters a lot to our society, so naturally social scientists have a few tools for researching it. Explore the ideas of age stratification and cohort flow, and test your understanding with a brief quiz.


I'm 27 years old. That's just one single number, but actually it can tell you a lot about my life. You know I was born in the late '80s, so I remember the world just before the information revolution of the late '90s and early 2000s. I grew up without social media, my childhood worldview was shaped by 9/11, and Obama was the first president I was legally old enough to vote for. You know that socially there's an expectation that by this point in my life I have received an education, I work full time, and there's a possibility that I'm married. Incidentally, all of these are true.

We put a lot of emphasis on age, and we expect age to tell us a lot about a person. Well, we're not the only culture to do this. Across history, the question of where people fit within society has often been one of the ages.

Age Stratification

How does your age affect your place within your society? In sociology, we often describe this through the idea of age stratification, the hierarchical ranking of people into age groups. One of the most obvious examples of this in American society is setting the legal age of childhood at 18, which means that anyone from newborn to 17 years old has limited political and social rights because they are not legally an adult. But once you've had your 18th birthday, you can vote, enlist in the military, pay your own taxes and make your own medical decisions. Your political rights are determined, in this case, by your age.

That's just one example from our modern culture. Age stratification has existed in many cultures across history and ranged from benefiting people of one age group to limiting the rights of people within another age group. When age stratification is used as a form of prejudice against an age group, we call this ageism. It's the same idea as racism or sexism, that someone is being unfairly targeted based on prejudicial assumptions. This was, for a little while, a problem in corporate America, when elderly workers were forced into retirement due to their age.

However, age stratification does not always mean ageism. From a pragmatic perspective, age stratification can help governments predict population trends. What's the estimated tax-paying workforce? How many people are currently receiving social security? How many people will need it in the future? How many children are the appropriate age for public schools, and how many will be likely heading to a public university? All of these things require budgeting and planning, so age stratification helps governments plan and prepare for the future.

Cohort Flow

One other way that social scientists look at this question of age within society is the cohort, a group of people who belong to the same age group or experiences within an age range. This can be as broad as children vs. adults or as specific as 35 year-olds who smoke regularly. Most commonly, when social scientists are specifically studying age and society, they rely on a birth cohort, or people born within the same year. So, anyone else born in 1988 would be in my birth cohort. Cohorts can be useful tools for studying how people's experiences directly relate to their age, especially within the context of social expectations.

As we discussed earlier, different age groups, different cohorts, often have different social expectations. When you're legally a child, society expects certain things from you. But once you become an adult, those expectations change. Really, you are constantly moving between different ranges of expectations based on your age. We call the movement of a cohort through an age role cohort flow. High-school children become adults, and middle-school children move up into the vacant role of high schoolers.

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