> I bet many would think n=100 would be worthless once the population reaches millions, or especially billions.
That depends on a uniform distribution of the population and an unbiased sampling method. One of the polls in the 2016 US presidential election [1] would shift Trump's position by a full percentage point based on input from a single man depending on which week he participated in the panel.
Yes, but if your sampling is biased then the solution is not simply a larger sample size. The only way in which larger sample sizes help is giving more power to any methods you use to try to control for sampling bias.
That depends on a uniform distribution of the population and an unbiased sampling method. One of the polls in the 2016 US presidential election [1] would shift Trump's position by a full percentage point based on input from a single man depending on which week he participated in the panel.
[1] https://www.nytimes.com/2016/10/13/upshot/how-one-19-year-ol...