The Law of Large Numbers

In statistics the law of large numbers states that as sample size increases the accuracy of population estimates increases. This is true for all distributions.

Example:
Suppose we had a bag of 100 marbles and wanted to know how many marbles were solid red.
We could start by drawing 10 marbles from the bag and finding that 2 are red. Thus we estimate that 20% are red.

Then we draw 50 marbles and find that 9 are red, thus we now estimate that 18% are red.

Finally, we draw all 100 marbles (census) and find that there are 17 red marbles. Or that 17% of the marbles are red.

In either case, as we drew more and more marbles our estimate got better and better. This is the law of large numbers.