Countries have incentives to manipulate population data. Most error that I’m aware of is not attributable to poor data quality. For example, if you have a real estate bubble you have a strong incentive to show population growth.

>For example, if you have a real estate bubble you have a strong incentive to show population growth.

That's one source of bias that is present at a specific time. Mostly you would have competing incentives. There is usually more than one agency that runs does the counting. Vital records registration, voter rolls and tax payers lists, for example are separate agencies in some countries. Not every tax payer is a voter and not everyone who was born still lives in the country. The sources are sometimes cross-referenced too. Then there is usually a place that needs to do macroeconomic forecasting and needs to have some numbers to do it's job.

I doubt places where the data is poor like Somalia or Afghanistan are making up their numbers because of a real estate bubble

Agree. I feel that it is beneficial to present yourself larger than you really are.

Not just that. Poorer countries inflate their numbers so they can get more financial aid