Scatterplots

Please view this tutorial and answer the follow-up questions on loose leaf or graph paper to be handed in to your

teacher.

Scatterplot Basics

• Scatterplots have an x and y axis that represent two sets of data

• They can be used to compare two sets of information or track trends over time

• You DO NOT connect the points in a scatterplot

• In previous graphs, we would often sort data to make graphing easier. You CAN NOT sort data in a scatterplot.

Making a Scatterplot

The height information will go on the x-axisand armspan will goon the y-axis.

Name Heights ArmspansJohn 156 154Sally 164 164Mary 162 163Bob 173 172

Kevin 165 168Sam 150 148Jen 148 148

Jared 172 171Betty 180 178Don 156 154

Since we have twosets of information, draw both ahorizontal and a vertical axis.(Disregard the names!)

Making a Scatterplot

Making a window for a scatterplot is slightly different than making a window for other graphs because you need to

worry about both the x and y axis.

For the x-axis, look at your x values and go a little lower than your lowest for the minimum and a little higher than the highest for your maximum.

For the y-axis, look at your y values and go a little lower than your lowest for the minimum and a little higher than the highest for your maximum.

Making a Scatterplot

Heights Armspans156 154164 164162 163173 172165 168150 148148 148172 171180 178156 154

Height (in cm)

Arm

span

(in

cm)

145 150 155 160 165 170 175 180

145

150

155

160

165

170

175

180

Choose your x min, xmax and xscl based on your height information.

Choose your y min, ymax and yscl based on your armspan information.

Don’t forget to label each axis! This is very important!

Making a Scatterplot

Height (in cm)

Arm

span

(in

cm)

145

145

150 155 160 165 170 175 180

150

155

160

165

170

175

180

Heights Armspans156 154

Next, you’ll need to plot the points.

Take our first pair of (height, armspan)

values.

Making a Scatterplot

Height (in cm)

Arm

span

(in

cm)

145

145

150 155 160 165 170 175 180

150

155

160

165

170

175

180

Heights Armspans156 154

Imagine that you draw a line up from 156 on the x-axis.

Mark your point where the two lines meet.

Imagine that you draw a line across from 154 on the y-axis.

Making a Scatterplot

Heights Armspans156 154164 164162 163173 172165 168150 148148 148172 171180 178156 154

Height (in cm)

Arm

span

(in

cm)

145

145

150 155 160 165 170 175 180

150

155

160

165

170

175

180

Now mark the rest of your points the same way.

Making a Scatterplot

Height (in cm)

Arm

span

(in

cm)

145

145

150 155 160 165 170 175 180

150

155

160

165

170

175

180

When using a scatterplot to make comparisons, sometimes it helps to make a y=x line.

This will help you figure out if the x-values are greater than the y-values or vice versa.

Making a Scatterplot

Height (in cm)

Arm

span

(in

cm)

145

145

150 155 160 165 170 175 180

150

155

160

165

170

175

180

Make sure that the y=x line goes through coordinates that have the same value for x and y.

Sometimes the line will go diagonally through the graph, other times it will not.It depends on your mins, maxs, and scales.

Making a Scatterplot

Height (in cm)

Arm

span

(in

cm)

145

145

150 155 160 165 170 175 180

150

155

160

165

170

175

180Points that fall exactly

on the line will have the same x-coordinate and y-coordinate.

Points that are above the line have y values that are larger than their corresponding x values.

Points that are below the line have x values that are larger than their corresponding y values.

y > x

y < x or x > y

y = x

Making a Scatterplot

Height (in cm)

Arm

span

(in

cm)

145

145

150 155 160 165 170 175 180

150

155

160

165

170

175

180Notice that we have

two points that are exactly on the line.

(148, 148)

(164, 164)

These points have values where x and y are equal.

Making a Scatterplot

Height (in cm)

Arm

span

(in

cm)

145

145

150 155 160 165 170 175 180

150

155

160

165

170

175

180Are heights or

armspans larger for this class?

There are six values below the y=x line. This means that six students had heights greater than armspan.

There is only one value above the y=x line which means only one student had an armspan that was greater than the height.

Since there are more points below the line, the heights are typically larger than the armspans for this class.

Creating a Scatterplot on the Calculator

1. Enter your data into a list2. 2nd Y=3. Select Plot 1 then

Highlight “On” and hit ENTER

4. Under Type select the first choice.

Creating a Scatterplot on the Calculator

5. Make sure that you identify your x information and y information in Xlist and Ylist.

6. Set your window.7. Hit Graph.

Follow Up Questions

Answer the following questionsand hand them in to your teacher.

Follow Up QuestionsTeam

Bat Rank

Pitch Rank

Colorado 1 15Houston 2 2San Francisco 3 7Atlanta 4 1Chicago 5 11Philadelphia 6 14Cincinnati 7 10Milwaukee 8 12New York 9 4St. Louis 10 8Pittsburgh 11 6San Diego 12 3Los Angeles 13 5Montreal 14 8Florida 15 16Arizona 16 13

1. Construct a scatterplot of these data pairs. Explain what the graph tells you about the relation between the teams’ batting and pitching.

2. Draw the y = x line on the scatterplot. Explain the relationship between the teams’ batting and pitching by looking at the points shown above, on, or below that line.