Notes for Lesson 12 – 2: Frequency and Histograms

Vocabulary:Frequency – The number of data items in an intervalFrequency Table – A table that groups a set of data values into intervals and shoes the frequency for

each intervalHistogram – A special type of bar graph that can display data from a frequency tableCumulative Frequency Table – A table that shows the number of data values that lie in or below the

given interval

12-2.1 – Making a frequency table

A frequency table is a chart that has divided the set of data into equal intervals then tells how many lie in that interval. You must make sure that the intervals do not overlap.

Examples:

Since the values range from 2 to 17 it would seem that intervals of 4 would be reasonable.Home Runs Frequency

2-5 46-9 4

10-13 314-17 3

12-2.2 – Making a Histogram

A histogram is a graph that displays the data from a frequency table. The intervals on the histogram must be the same as the frequency table. The height of the bar must match the frequency of the interval.

Examples: (also see histogram for the table from 12-2.1

012345

2 - 5 6 - 9 10 - 13 14 - 17

12-2.3 – Interpreting Histograms

Histograms can be described by their shape. If each of the bars are about the same height the histogram is said to be uniformed. If a vertical line can divide the histogram into two parts that are close to mirror images it is symmetric. If the histogram has a peak that is not in the center then it is skewed.

Uniform Symmetric Skewed

12-2.4 – Making a cumulative frequency table.

To make a cumulative frequency table you add a third column that will add up each interval frequency as you go.

Example: