A Short Explanation of the “Tempo Effect”

[This is part of my series on Thomas Malthus’ “Essay on the Principle of Population,” first published in 1798. You can find an overview of all my posts here that I will keep updated: “Synopsis: What’s Wrong with the Malthusian Argument?”]

Here comes another installment in my mini-series on how to spot charlatans writing on demographics. Unfortunately, there are very many of them around and they have shaped the views of the public for decades.

The top telltale sign in my experience is when someone argues with birth and death rates instead of fertility and mortality. The former depend on population structure, which may mean that they are seriously misleading if taken as a snapshot, the latter do not.

It’s worse, but by no means uncommon, when someone does not even realize these concepts are distinct and calls birth rates “fertility” and death rates “mortality.” If you are interested, here is a post where I explain all this more in detail: The Best Way to Spot Demographic Nonsense.

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This is a pretty basic mistake, yet a very popular one. But then there are some “advanced” signs you will find with more sophisticated charlatans. They may get birth rates v. fertility and death rates v. mortality right, but they are still unaware of certain fundamental concepts that are relevant in many situations. My favorite indicators here are “population momentum” and the “tempo effect.”