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2-7 Bar Graphs & Histograms

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2-7 Bar Graphs & Histograms

Pages 85-89

Indicators

D1 -Read and create graphs

D2 -Analyze how decisions about graphing affect the graphical representation

There are two differences

- The type of data that is presented
- The way they are drawn

Bar graphs are usually used to display "categorical data", that is data that fits into categories.

For example suppose that I

offered to buy donuts for six

people and three said they

wanted chocolate covered,

2 said plain and

one said with

icing & sprinkles.

Histograms are usually used to present "continuous data", that is data that represents measured quantity where, at least in theory, the numbers can take on any value in a certain range.

A good example is weight. If you measure the

weights of a group of adults you might

get and numbers between 90 lbs. and

240 lbs. We usually report our weight as

pounds or to the nearest 1/2 lb. but we

might do so to the nearest 1/10 lb.

depending on how accurate the scale is.

To make a histogram…

- Remember: A histogram is a particular kind of bar graph.
- The data that is being represented is in intervals…
- So…to organize your data, make a
- Frequency table first!

Weights of adults

40

30

20

10

# of people

90 I 150 I 210 I

Pounds

The weight data would then be collected into categories to present a histogram.

For Example:

might be a histogram for weights (with the appropriate scale on the vertical axis). Here the data has been collected into categories of 30 lbs.

- A histogram is a particular kind of bar graph.
- If you make a bar graph of the favorite colors of children in Mrs. Flaherty's 4th grade class (6 for pink, 8 for blue, 1 for black, etc.) that doesn't qualify as a histogram, because the colors don't correspond to any numerical values, and their order is arbitrary.
- A different kind of example: you could make a bar graph of monthly returns on your stock investment in January, February, etc. Here, there IS a natural order to the bars, but it still doesn't qualify as a histogram.

- A histogram is a bar graph of frequencies of different numerical values within a population. The most straightforward kind of example may be a bar graph of the number of 4th grade students by height: how many between 4' and 4'1" between 4'1" and 4'2" between 4'2" and 4'3"
- Both axis use numbers!

Pg. 88 #14-16 and Pg. 569 #1-4