Step by step
The question
Question: draw a scatter plot of (10, 40), (20, 55), (30, 50), (40, 70), (50, 80), (60, 85).
What is the correlation?
Correlation tells if y goes up or down as x goes up, and how closely.
1 Draw the axes
x goes along the bottom, in 10s.
y goes up the side, in 10s.
2 Plot the points
(10, 40): across to 10, then up to 40.
(20, 55): across 20, up 55.
And so on, one dot for each point.
3 Find the direction
We draw a line along the points.
It goes uphill: from bottom left to top right.
As x goes up, y goes up too.
That is a positive correlation.
4 Find the strength
Two lines hold all the points.
The band is narrow: the points stay close to a straight line.
So the correlation is strong.
Careful!
A correlation shows that two things move together.
It does not prove that one causes the other.
So the answer: strong positive correlation.
5 Check
Let's check with numbers.
The 3 points on the left have a mean y of about 48.3.
The 3 on the right: about 78.3.
The right is higher: it goes up.
So it is right!
Let's look back.
First: draw the axes.
Then: plot the points.
Then: find the direction.
Then: find the strength.
Last: check.