A great example to show power of visualizing data: Anscombe’s Quartet Table

Let’s look at four datasets which have identical statistical properties:
Here’s the DATA:

Here’s their statistical properties:

Property Value Mean of x in each case 9 (exact) Variance of x in each case 11 (exact) Mean of y in each case 7.50 (to 2 decimal places) Variance of y in each case 4.122 or 4.127 (to 3 decimal places) Correlation between x and y in each case 0.816 (to 3 decimal places) Linear regression line in each case y = 3.00 + 0.500x

They look identical – don’t they? BUT let’s visualize the data:

Only visualizing data made it possible for us to understand and appreciate the “difference” between data-sets. Looking at just statistical properties made them appear “similar” – moral of the story: Visualize data! Graph data along with investigating statistical properties.

Source: Anscombe’s quartet