7.1 Three ways to understand change
Before we evaluate real examples, it will be helpful to understand different kinds of societal change. Let us work with a toy example. Suppose the newspaper (your favourite one) headline tomorrow states: “Average walking speed of Singaporeans slower than 10 years ago”. There are three possible explanations for this (maybe more, this is not a perfect analogy).
Older people walk slower, and Singapore is an ageing society (average age is rising), so its average walking speed will fall as there are more older people in society.
Those born later (e.g., Millenials, Gen Z) are walking slower than those born earlier (e.g., Baby Boomers), bringing down our average walking speed.
There was an alien invasion this year and many aliens suddenly came to live among us. This suddenly caused overpopulation, since our system is only prepared for 6.9 million. People in Singapore thus have to lower their walking speed this year because it has become very crowded compared to last year.
The last one is slightly facetious, but as you can see, the three explanations point to three quite different reasons for change. We will look at each one, in order.
Change with age: Age effects refer to changes over the life course that apply to all individuals as they grow older. This is best demonstrated in terms of physical and biological changes that occur as we age (e.g., our metabolism slows down, we get wrinkles etc.) - such changes tend to be common to all of us, regardless of when we were born, or what era we live in.
Change with cohort: Cohort effects are probably easiest to think about as generational change (i.e., change with birth cohorts), even though more generally they are used refer to a group of individuals that have gone through shared experiences (e.g., school cohorts). When you hear remarks from people such as “young people nowadays are [such strawberries / so spoilt / have no manners]”, this is usually the kind of change they are suggesting has happened.
Change with period: Period effects are changes due to contextual factors that affect all living persons at a particular point in time. For instance, significant events such as wars, epidemics, or natural disasters affect everyone who is exposed to it regardless of age.
Social scientists have long recognized the need to think clearly about these three distinct ways of understanding social change54. Popular discourse, however, tends to ignore the meaningful differences between these concepts - a common error is making conclusions about cohort change based off period data. We will examine two instances of this.