[insane_dreamer]

Doesn’t every country or at least major country conduct censuses? Assuming there are some countries that can’t or don’t due to conflict, lack of resources etc. it seems these would be limited and therefore whatever estimates are made for those countries would be off my millions but certainly not billions.

[Ekaros]

No. Some countries don't need "census" as every citizen is sufficiently tracked and must report their official address. And so would most migrants. Meaning that with modern computer databases you can track births, deaths, immigration and emigration down to single person.

[epolanski]

I'm not aware of any country not doing censuses regardless of their digitization.

Censuses aren't just counts, they are timestamps of lots of data (education, family, etc) which is often missing, not digitized or not available (you may graduate in a different country, you might be living with someone but not be married, etc).

There's also a privacy/anonimity issue, even when data is available it can be used for very little over than counting.

[insane_dreamer]

Ok but that is even more accurate than a census. So which countries are these uncounted people located?