http://www.ck12.org Chapter 7. Organizing and Displaying Data - Basic
7.2 Bar Graphs, Histograms and Stem-and-Leaf Plots
Learning Objectives
- Construct a stem-and leaf plot.
- Understand the importance of a stem-and-leaf plot in statistics.
- Construct and interpret a bar graph.
- Create a frequency distribution chart.
- Construct and interpret a histogram.
- Use technology to create graphical representations of data.
Introduction
Suppose you have a younger sister or brother and it is your job to entertain him or her every Saturday morning. You
decide to take the youngster to the community pool to swim. Since swimming is a new thing to do, your little buddy
isn’t too sure about the water and is a bit scared of the new adventure. You decide to keep a record of the length of
time they stay in the water each morning. You recorded the following times (in minutes):
12 , 13 , 21 , 27 , 33 , 34 , 35 , 37 , 40 , 40 , 41
Your brother or sister is too young to understand the meaning of the times that you’ve recorded so you decide that
you have to draw a picture of these numbers to show to the child. How are you going to represent these numbers?
By the end of this lesson you will have several ideas of how to represent these numbers and you can choose the one
that you think your little buddy will understand the best.
Bar Graphs
A bar chart orbar graphis often used for data that can be described by categories (months, colors, activities... )
which is referred to as qualitative data. A bar graph can also be used to represent numerical data (quantitative data)
if the number of data is not too large. A bar graph plots the number of times a category or value occurs in the data
set. The height of the bar represents the number of times the value or the observation appeared in the data set. The
y−axismost often records the frequency and thex−axisrecords the category or value interval. The axes must be
labeled to indicate what each one represents and a title should be placed on the graph. When a bar graph is used
to display qualitative data, the data is grouped in bins or intervals. These bins and the frequency of the data that is
located in each bin can be shown in a frequency distribution table. For a bar graph, there is a break between the bins
because the data is not continuous. The bins for a set of data could be grouped with a bin size of 10 and be written
as 10− 19 , 20 −29 and 30−31.
Example 1: Sara is doing a project on winter weather for her Science project. She has decided to research the
amount of snowfall (in inches) that fell last year for cities in Canada. Here is the information that she has collected:
TABLE7.4:
City Snowfall
Vancouver 22
Edmonton 54.2
Regina 43
Toronto 54
Ottawa 88.6