Scatter plots

Scatter plots, also called scatter graphs, are used to show relationship between two sets of data by writing them as ordered pairs.

To illustrate, let us pretend that you have a business that sells notebooks.

Day 1, you sell 10 notebooks

Day 2, you sell 5 notebooks

Day 3, you sell 15 notebooks

Day 4, you sell 10 notebooks

Day 5 , you sell 20 notebooks

Day 6, you sell 15 notebooks

Day 7, you sell 30 notebooks

Day 8, you sell 15 notebooks

Day 9, you sell 25 notebooks

Day 10, you sell 15 notebooks

You can display this situation with ordered pairs as shown below:

(1,10), (2,5), (3,15), (4,10), (5,20), (6,15), (7,30), (8,15), (9, 25), and (10, 15)

Then we can put the ordered pairs on the coordinate system. The resulting graph is called a scatter plot or scatter graph.

Notice how the points are scattered around and everything is located in the first quadrant.

Scatter plot

Scatter plots and the three types of correlation

Two sets of data can form 3 types of correlation.

What is a positive correlation?

When y increases as x increases, the two sets of data have a positive correlation.

Basically, when you closely examine the graph, you will see that the points have a tendency to go upward.

Example

Scatter with strong positive correlation

Not only the points have a tendency to go up, they are also very close to one another. In other words, they are not scattered far apart from one another. This type of correlation, as seen in the graph above, is called strong positive correlation as well.

On the other hand, when the points have a tendency to go up yet they are scattered far apart from another, the graph has a weak positive correlation. The graph below has a weak positive correlation.

Scatter with weak positive correlation
What is a negative correlation?

When y decreases as x increases, the two sets of data have a negative correlation.

Basically, when you closely examine the graph, you will see that the graph has a tendency to go downward.

Example

Scatter plot with strong negative correlation

Not only the points have a tendency to go down, they are also very close to one another. This type of correlation, as seen in the graph above, is called strong negative correlation as well.

On the other hand, when the points have a tendency to go down yet they are scattered far apart from another, the graph has a weak negative correlation. The graph below has a weak negative correlation.

Scatter with weak negative correlation
When x and y are not related, we say that the two sets of data have no correlation.

Example

Scatter plot with no correlation

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