Imagine you have a big jar filled with lots of different colored marbles. Now, suppose you want to pick out a few marbles from the jar and see how many of each color you got.
Ewens's Sampling Formula is like a special way of counting these marbles. It helps you figure out how likely it is that you'll pick certain colored marbles based on how many there are in the jar.
So, let's say you have 10 red marbles, 8 blue marbles, and 5 green marbles in the jar. Ewens's Sampling Formula tells you that if you randomly pick out three marbles, there are different ways this could happen.
For example, you might get one red marble, one blue marble, and one green marble. Or you might get two red marbles and one blue marble. Ewens's Sampling Formula helps you figure out how many of these different combinations are possible, taking into account the different number of marbles of each color.
Why is this helpful? Well, it's often used in genetics research to help scientists understand how certain traits or genes are passed down through different generations. Instead of marbles, they might be looking at different types of DNA sequences. But Ewens's Sampling Formula allows them to predict how likely it is that certain sequences will be passed down based on how common they are in the population.