How large a sample size is needed to we could get accurate results for a population?

[Magnolia]

If representative ... yeah thats what is going on.

[Peterski]

Does for example this Czech sample look fake?:

https://www.sendspace.com/file/ilz9yn

[Graham]

If representative ... yeah thats what is going on.

If the spread in a population ( a large sample size) has a wide range and separate clusters on both ends then there's an argument for smaller groups( still ok sized) split up from that for example. If a big group huddles near its median/mean, then keep it as one.

But a sample population should not have a large range, then you have an error.

[Magnolia]

It is about statistics, not about anything else.
There are statistical methods for the sample size determination to we could get accurate information about a typical/average person/to we could determinate a typical/average person.

The approach to take one random person and claim that person is typical for a region is error.

[Dick]

Gedcom tells you nothing about the ethnic origin of someone, only a genealogical tree, just names. They could all be Jewish mulattos with German names for all we know. That's why studies don't rely on that, they just filter from the beginning the most oddly non ethnic with the 4 GP requirement, then they run and plot them to actually verify their admixture, which is what matters genetically, not a name or a place of birth/death.

You also fail to understand why they purposedly kept those "outliers" on top of their baseline average, they are a significant portion of x pop even if outlying compared to the majority, they do need to stay in the average run in the right proportion.

[Karol Klačansky]

A sample size should be over 30 at least, and then the bigger the better. .

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[Lotus Star]

Hundreds or thousands out of how many people in total, one hundred thousands, one million, etc?

It depends on how large a population is. There is a ratio.

[Laberia]

It depends on how large a population is. There is a ratio.

Let simplify a litle bitt our discussion.
We have a region, region N. This region is inhabitated by 1.000.000 people. You are a team leader of a group of geneticists and your duty is to determine the haplogroups present in the population of region N and the percentages for every haplogroup. First way is testing the inhabitants one by one but of course this is not possible for the moment, maybe in the future. So, you have to start to select some people to test. How many people you have to test from the inhabitants of the region N and how they are selected in order to have an acceptable result? I mean the minimum of samples.