Graphing Data

3 Types of Graphs

• Bar Graph• Line Graph• Circle (or Pie) Graph

Bar Graph

Useful for graphing items with different categories

Bar Graph

“Game of Life” Salaries

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Business Teacher Journalist Doctor

I can change the order.

Bar Graph

“Game of Life” Salaries

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Doctor Journalist Teacher Business

Does this change the information?

Bar Graph

“Game of Life” Salaries

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Business Doctor Journalist Teacher

Whatever helps me get the point across

Circle Graph

Satisfaction with the Temperature in Mr. Jackson’s

Room5% 2%

53%

40%

Too Cold

Too Hot

UndecidedJust Right

Ideal for showing percentages(fractions)

All the parts add up to a whole

To find the percentage

• Divide the number in whichever category by the total number.– 10 students are too hot– 12 students are too cold– 2 students aren’t sure– 1 Teacher thinks it is just right

• The total is 25

To find the percentage

• 10/25 = 40% are too hot• 12/25 = 48% are too cold• 2/25 = 8% aren’t sure• 1/25 = 4% is just right

• When making the graph:– 1 circle is 360° = 100%– Each percent is 3.6°

Line graph

• A line graph is useful when a dependent variable changes due to a relationship with an independent variable.

• The independent variable is “x”• The dependent variable is “y”

Line graph

• We’ll start with an experiment.

Line graph

• As we turn the knob, we will take data. The knob location will be x, and the gauge reading will be y.– x=½ and y=0– x=1 and y=1– x=2 and y=3– …and so on

Let’s look at our data

• Let’s make a table with our data.

• It may be helpful to sort the data by the independent variable.

X Y½ 01 12 30 -1-1 -3

X Y-1 -30 -1½ 01 12 3

Let’s look at our solutions

• Now let’s plot the solutions on a graph.

X Y-1 -30 -1½ 01 12 3

Tow the line!

• It is reasonable to use the line as the solution rather than just the points.– Interpolation– Extrapolation

If it doesn’t fit…

• Usually, real data doesn’t fit on a perfect line.

• DO NOT play “connect the dots”.

• Make a “regression” line, or “best fit” line.

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If it doesn’t fit…

• Usually, real data doesn’t fit on a perfect line.

• DO NOT play “connect the dots”.

• Make a “regression” line, or “best fit” line.– “Eyeball” it– Use Excel 0

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It doesn’t look square!

• We won’t always have a straight line on a graph.

• This is a parabola. It is common in science graphs.

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It doesn’t look like anything!

• Often, we can write an equation for a graph.

• Sometimes we can’t.

• That’s okay.

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Assignment

• p. 26, 1-5• Worksheet

• Chapter 1 Test Friday 8/27

• Bring Index Cards tomorrow