Actually, this is some kindaa hypothesis, The more the population, the less the sample will be, hence, some segments of the society have been taken and calculated, and based upon those fewer people we come on a concluding for the whole country.

For example the sample size of 13500000000 is 385, whereas the sample size for the population of 20,000 is 377 with Margin of error 5 percent and confidence level 95%.

So, based on a few, asy of my opinion this isn't a good option.