# What is Statistics

## A Case Study

We have a problem.

In our lab, we found **a huge amount of similar robots on a planet** (**physical population**). To know more about **the weight of these robots** (**statistical population**), we first need to **choose some of them** (**physical sample**), then obtain **the weight of them** (**statistical sample**).

To describe the data, we could calculate the mean of the weight. We found that the mean weight is 93kg (**descriptive statistics**).

How can we know the mean weight of this kind of robot? We know the mean weight of those robot that we selected. We need a link to the actual mean weight of all the robots on the planet (**inferential statistics, estimation**).

In the end, we will have a conclusion of the mean weight of all the robots on the planet. Then again, how could we be sure that our conclusion is correct (**hypothesis testing**)?