HOW
TO CHOOSE WHICH TYPE OF GRAPH TO USE?
When to Use . . .
. . . a Line graph.
Line
graphs are used to track changes over short and long periods of time. When
smaller changes exist, line graphs are better to use than bar graphs. Line
graphs can also be used to compare changes over the same period of time for
more than one group.
. . . a Pie Chart.
Pie
charts are best to use when you are trying to compare parts of a whole. They do
not show changes over time.
. . . a Bar Graph.
Bar
graphs are used to compare things between different groups or to track changes
over time. However, when trying to measure change over time, bar graphs are
best when the changes are larger.
. . . an Area Graph.
Area
graphs are very similar to line graphs. They can be used to track changes over
time for one or more groups. Area graphs are good to use when you are tracking
the changes in two or more related groups that make up one whole category (for
example public and private groups).
. . . an X-Y Plot.
X-Y
plots are used to determine relationships between the two different things. The
x-axis is used to measure one event (or variable) and the y-axis is used to
measure the other. If both variables increase at the same time, they have a
positive relationship. If one variable decreases while the other increases,
they have a negative relationship. Sometimes the variables don't follow any
pattern and have no relationship.
When you watch the
news on television - particularly news that centers of business and investing -
you have probably noticed a number of colorful graphics used to describe and
track trends. These graphics are generally graphs and charts and they are
critical for clearly conveying information in an easy to understand manner as
well as in a way that the difference between two different pieces of data is
clearly drawn. In a way, graphs and charts are illustrative methods of clearly
presenting various types of differences in a clear method. Of course, not all
charts and graphs are the same because certain charts and graphs and more
appropriate for one type of comparison than another. These graphs/charts
generally fall into three different categories: line graphs, bar graphs and pie
charts. Each of these three has their own particular similarities and
differences all of which need to be examined for a better understanding.
A line graph provides
a means in which to compare two different types of information through showing
how they are similar and how they are differ. This is performed through the use
two lines each representing the two aforementioned pieces of information which
are then charted along a numerical scale. A common example of a line graph
would be two lines with one line showing the level of unemployment in the city
of Los Angeles and one line showing the unemployment in New York City. The
graph the lines run can represent the years 1978 to 2008 and the "ups and
downs" of the unemployment rate of each city over the course of 20 years
can be accurately compared.
Line Graph Example
A bar graph is very
similar to a line graph in the sense that it is designed to show different
values of two or more subjects but instead of using lines it using horizontal
and vertical bars that represent a different value. There are numbers along the
side of a bar graph and they are scales identical to what would be found on a
line graph. In a way, this type of graph is somewhat easier to read than a line
graph and it conveys informational equally as well.
Bar Graph Example
A pie chart serves
the same purpose of a line graph and a bar graph in the sense it is designed to
show differences between two separate subjects although it eschews the common
linear style found in the two other graphs. A pie chart is a very common type
of graph that is in the shape of a circle with the circle representing a
collective of 100%. Then, within the circle smaller percentage portions within
the 100% will be presented in different colors. Sometimes the shapes look like
slices taken out of a pie and this is where it gets the nickname of a pie
chart. An example of a chart could include a question who likes to play
Playstation III with the pie cut in half with 50% colored to represent teens,
and two 25% "triangles" representing children and adults. It is
probably the easiest chart to read and is commonly used in marketing and
business presentations.
Pie Chart Example
Examining X-Y (Scatter) Plots
X-Y
plots, or scatter plots, can be used to see if one event affects another event.
For example, if you spend more hours studying, will you get better grades? The
following pages describe the different parts of an x-y plot.
The Title
The
title offers a short explanation of what is in your graph. This helps the
reader identify what they are about to look at. It can be creative or simple as
long as it tells what is in the graph. The title of this graph tells the reader
that the graph contains information about the difference in money spent on
students of elementary and secondary schools from different countries.
The Legend
The
legend tells what each point represents. Just like on a map, the legend helps
the reader understand what they are looking at. Each of the colors in this
legend represents a different country.
The Source
The
source explains where you found the information that is in your graph. It is
important to give credit to those who collected your data! In this graph, the
source tells us that we found our information from the Organization for
Economic Cooperation and Development.
Y-Axis
In x-y
plots, the y-axis runs vertically (up and down). Typically, the y-axis has
numbers for the amount of stuff being measured. The y-axis usually starts
counting at 0 and can be divided into as many equal parts as you want to. In
this line graph, the y-axis is measuring the Gross Domestic Product (GDP) of
each country.
The Data
The
most important part of your graph is the information, or data, it contains.
Line graphs can present more than one group of data at a time. In this graph,
two sets of data are presented.
X-Axis
In x-y plots, like
the one above, the x-axis runs horizontally (flat). Typically, the x-axis has
numbers representing different time periods or names of things being measured.
In this plot, the x-axis measures the amount of money spent by a country on
elementary and secondary education per child.
Analyzing Area Graphs
Like
line graphs, area graphs can be used to show how something changes over time.
They can be used when you're plotting data that has peaks (ups) and valleys
(downs), or that was collected in a short time period. The following pages
describe the different parts of an area graph.
The Title
The
title offers a short explanation of what is in your graph. This helps the
reader identify what they are about to look at. It can be creative or simple as
long as it tells what is in the graph. The title of this graph tells the reader
that the graph contains information about the changes in enrollment of
elementary and secondary schools from 1970 to 2000.
The Legend
The
legend tells what each shaded area represents. Just like on a map, the legend
helps the reader understand what they are looking at. This legend tells us that
the blue area represents enrollment in public schools and the yellow area
represents enrollment in private schools.
The Source
The
source explains where you found the information that is in your graph. It is
important to give credit to those who collected your data! In this graph, the
source tells us that we found our information from the NCES.
Y-Axis
In area
graphs, the y-axis runs vertically (up and down). Typically, the y-axis has
numbers for the amount of stuff being measured. The y-axis usually starts
counting at 0 and can be divided into as many equal parts as you want to. In
this area graph, the y-axis is measuring the number of students enrolled in
public and private schools.
The Data
The
most important part of your graph is the information, or data, it contains.
Area graphs can present more than one group of data at a time. In this graph,
two sets of data are presented.
X-Axis
In area
graphs, like the one above, the x-axis runs horizontally (flat). Typically, the
x-axis has numbers representing different time periods or names of things being
compared. In this area graph, the x-axis measures different school years.
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