The Cohort Effect in Various Fields

Despite being used since 1927, the cohort effect did not become popular until the end of the 20th century.

The previous century saw two of the most tragic events in entire human history - the two World Wars. It is estimated that, together, they caused the death of anywhere between 55 to 150 million people. But these casualties weren't the only mark they left behind; millions more were scarred by the experience itself.

One can't help but wonder what it must have been like to grow up in those times? It is obvious that such powerful events forever change the outlook of those who live through them. The term 'cohort effect' is used to study the impact of such significant events on groups of people.

For example, people who reached adulthood in the 1940s were less likely to indulge in risky endeavors like drug abuse and premarital sex. On the other hand, those who reached adulthood in the '90s were more likely to indulge in such behavior, though they were less likely to have polio, as compared to the previous group.

The term 'cohort' is a group of people who share a common characteristic, such as the same birth date. One of such cohorts may have faced a significant event, such as an economic depression, war, or epidemic outbreak, which will shape the characteristics, values, and beliefs of its members.

For this reason, cohort effects are important in sociology, especially in medically sociology, to understand how such cultural factors affect the health of populations, and in epidemiology to understand their relation with disease outbreaks. Given here are some examples of cohort effect.

A popular cohort effect in the UK is the reduction in mortality rates for people born between 1925 and 1945. People born before and after this period do not show the same longevity.

This improvement has been attributed to a reduction in infectious disease outbreaks, food rationing during the Second World War, reduction in smoking, and for the simple reason that this group was too young to enlist when the War broke out in 1939.

The number of deaths due to cervical cancer increased rapidly until the first half of the 20th century. However, beginning in 1950, many countries, including China, Spain, and Brazil saw a reduction in this death toll.

For example, in China, few women died in the years 1970 - '92, because the country passed a ban on brothels and a strict one-child policy, which reduced the sexual transmission of the cervical-cancer-causing HPV virus.

Beginning in the 1960s, Brazilian cities like São Paulo and Rio de Janeiro also saw lesser mortality because of improved healthcare, along with the sexual and cultural revolution of the same period which resulted in women empowerment.

Studies indicate that US youth of the 1960s and early '70s were more involved in politics than the youth of the periods before and after. This group was less supportive of the existing political and social conditions, even as compared to their parents.

This was the period when the Vietnam War was in full swing, and owing to controversial policies of the time, youth who weren't even of voting age could be enlisted in the military. So, there was a real chance that these youth could be sent to the war zone and lose their lives.

If a survey was taken in 1970 for 30 year-old people, it would include those born in the year 1940 in the early phase of the Second World War and after the Great Depression had ended. If such a survey was taken in the year 2010, it would include those born in 1980, after the end of the Civil Rights Movement and the last US moon landing.

By the time of the survey, the former cohort (group) would have seen the early years of television, and the latter cohort would have seen the rapid growth of computer and internet technology. So, each cohort would have been affected by separate incidents, and show separate cohort effects.

In the same way, someone who attended elementary school in New York at the time of the 9/11 terror attacks would have a different perspective of life, than another cohort attending elementary school during peacetime.

A common cohort effect seen in engineering schools across the world is of new students choosing their programs according to the current job market.

This entire cohort, probably having students of the same age, takes similar decisions because of similar conditions of the job market at the time of admission. This creates newer requirements, such as varying class size that the school administration and faculty have to cope with.

Young employees joining an organization form a cohort, which requires training by senior employees. Such large, young cohorts can create a strain on the organization's resources. Over time, many different cohorts can make their way into the workplace.

The values and beliefs of each cohort can affect the resource management of the organization as these employees climb up the professional ladder. The values of the organization itself can be affected, depending on which cohort rises to influential positions.

A lot of confusion exists between the cohort vs. period effect in sociology. While the former deals with a single group of the same age (cohort), the latter describes the effects that a significant event has on a population across many age groups.