Scatter Plots

A graph of plotted points that show the relationship between two sets of data. In this example, each dot represents one person's weight versus their height. (The data is plotted on the graph as "Cartesian (x,y) Coordinates")

Example:

The local ice cream shop keeps track of how much ice cream they sell versus the temperature on that day. Here are their figures for the last 12 days:

Ice Cream Sales vs Temperature
Temperature °C	Ice Cream Sales
14.2°	$215
16.4°	$325
11.9°	$185
15.2°	$332
18.5°	$406
22.1°	$522
19.4°	$412
25.1°	$614
23.4°	$544
18.1°	$421
22.6°	$445
17.2°	$408

And here is the same data as a Scatter Plot:

It is now easy to see that warmer weather leads to more sales, but the relationship is not perfect.

Line of Best Fit

You can also draw a "Line of Best Fit" (also called a "Trend Line") on your scatter plot:

Try to have the line as close as possible to all points, and as many points above the line as below.

Example: Sea Level Rise

A Scatter Plot of Sea Level Rise:
And here I have drawn on a "Line of Best Fit".

Correlation

When the two sets of data are strongly linked together we say they have a High Correlation.

• Correlation is Positive when the values increase together, and
• Correlation is Negative when one value decreases as the other increases

Like this:

(Learn More About Correlation)

Negative Correlation

Correlations can be negative, which means there is a correlation but one value goes down as the other value increases.

Example : Birth Rate vs Income The birth rate tends to be lower in richer countries.   Below is a scatter plot for about 100 different countries.

Country Yearly Production per Person Birth Rate Madagascar $800 5.70 India $3,100 2.85 Mexico $9,600 2.49 Taiwan $25,300 1.57 Norway $40,000 1.78

It has a negative correlation (the line slopes down)

Note: I tried to fit a straight line to the data, but maybe a curve would work better, what do you think?