CK-12 Probability and Statistics - Advanced

2.1. Histograms and Frequency Distributions http://www.ck12.org

TABLE2.5:(continued)

Liters per Person Frequency

[ 100 − 110 ) 1

[ 110 − 120 ) 0

[ 120 − 130 ) 1

[ 130 − 140 ) 1

[ 140 − 150 ) 2

[ 150 − 160 ) 0

[ 160 − 170 ) 2

[ 170 − 180 ) 0

[ 180 − 190 ) 1

Figure:Completed Frequency Table for World Bottled Water Consumption Data(2004)

Notice the mathematical notation used for each classification. A bracket [ or ] indicates that the endpoint of the
interval is included in the class. A parentheses ( or ) indicates that the endpoint is not included. What do you do with
a number that is in between two classifications? For example, it is unlikely, but possible that a country consumed
exactly90 liters of bottled water per person. It is intuitive to include this in the90 s, not the 80 s, but how would we
label the categories? If you wrote 80−90 and 90−100, it would seem as if 90 belongs in both classes. But if you
wrote80−89, what would you do with 89.5? It is common practice in statistics to include a number that borders
two classes in thelargerof the two. So,[ 80 − 90 )means this classification includes everything from 80 that gets
infinitely close to, but not equal to 90. Even if the bracket notation is not used, you should always place such values
in the higher classification.

Histograms, Not Bar Graphs!

Once you can create a frequency table, you are ready to create our first graphical representation, called a histogram.
Let’s revisit our data about student bottled beverage habits.

TABLE2.6:

Number of Plastic Beverage Bottles per Week Frequency

1 1

2 1

3 3

4 4

5 6

6 8

7 7

8 2

Figure:Completed Frequency Table for Water Bottle Data

Here is the same data in a histogram: