We just sampled two groups of points (red and blue), and fit a regression line to each one.
How much confidence do we have in these fitted linear models? This page shows three variations of randomization tests that show us what regression lines from "similar" datasets would look like. The buttons at the top will sample a random, but similar, dataset in one of three ways. We will then fit regression lines for the randomized dataset, and then go back to the original data.
Comparing the "real" line to these replicated lines can tell us whether the original line tells us something interesting about the dataset, or if it's just fitting random noise. The numbers at the top will tell us how many of the replicated models have had a greater slope than