3.5 Sample size and population size

If we are trying to learn about a population based on a sample, it seems reasonable that the sample size and the population size ought to matter. We explored the effect of sample size and population size in the previous two course activities. The results were surprising! It turns out sample size does matter, but population size does not!

The key points are:

Key points: Sample size and population size

• Neither sample size nor population size affects bias. An unbiased sampling method is unbiased regardless of the sample size. And if we use a biased sampling method, it will not become less biased simply by making the sample size larger.

• Sample size affects sampling variability. Larger samples have less sample-to-sample variability.

• Population size does not matter! A representative sample of 25 is just as good when it comes from a small population as when it comes from a big population.