Principal stratification

Okay kiddo, listen up! Today we are going to learn about something called "principal stratification." It sounds like a big word, but I will make it easy for you to understand.

Think about your class at school, where you have boys and girls. Now imagine that your teacher wants to know how many kids in your class like pizza. But, she also wants to know if boys and girls like it equally or not. So, she decides to divide you all into two groups - one group of boys and another of girls. These two groups are called "strata."

Now, let's go back to the topic. Principal stratification is like dividing people into different groups, but it is done based on something else - not based on boys and girls. It is based on something called "principal stratum."

The "principal stratum" is a hidden group of people with a specific characteristic that we can't measure directly. Suppose, we want to know if a new medicine is more effective in treating a disease. We can't just give the medicine to everyone and see what happens. We might have to divide people into two groups based on some other factors, such as the stage of the disease or the severity of the symptoms.

By doing that, we create two principal strata - one group of people who will benefit from the medicine and another who won't. Now we can compare the outcomes of these two groups without worrying about other factors that may have distorted the results.

To sum up, principal stratification is a way to divide people into subgroups based on a hidden characteristic, which helps us to compare outcomes between these groups more accurately.