Transcript Making and Interpreting Graphs

Week 4
LSP 120
Joanna Deszcz
3 Types of Graphs used in QR

Pie Charts
 Very limited use
 Category sets must make a whole

XY Graphs or Line Graphs
 Use with “a lot” of data points

Bar Charts or Column Charts
 Very flexible
 Work well with limited data
 Compares more than one series
Pie Charts



Only used when have
a quantitative variable
associated with a list
of categories
Both the categories
and the quantities
each add up to a
whole
Categories must be
disjoint – no
overlapping
Most Common Pie Chart
Mistakes
Use on set of categories that don’t make
a whole
 Use on categories that overlap
 Include total in chart data


Let’s try an example
 Leading Causes Of Death Tab
Creating a Pie Chart



Select labels and
values
Choose Pie chart type
Choose layout
 Must include % value,
title and labels
 Layout 6 does it all

Add the source in a
text box
Labeling the Chart

Title should be descriptive
 Consider who, what, when and where

Percents should be formatted to 2
decimal places
 Format – Data Labels – Numbers –
Percentage – 2 decimal places

Source – add in text box
 Insert – Text Box – Draw text box on the
chart and type in source
 If not source give type “Unknown”
Chart Themes
Found on Page Layout Tab
 Slide mouse over built-in themes

 Chart will change to reflect each theme
The Result…
Flow Theme applied to the chart
XY Graphs



Used with a lot of
data
X-axis categories
are numeric, (often
years)
Choose xy graph
option with
connected data
points
3.5
3
2.5
2
1.5
1
0.5
0
1999
2000
2001
Note: Don’t use the Line Graph

Excel line graphs always treat the x-axis
categorically instead of numerically

Causes endless array of mistakes

Use XY (Scatter) graph instead to avoid
errors

Let’s try one
 Lake Michigan Levels Tab
Creating XY (Line) Graphs


Select category
labels and values
Choose Scatter
chart option
 Scatter with straight
lines and markers
type
 2nd row, 2nd column

Choose design
layout 1 from Design
tab
Labeling the Chart

Title should be descriptive
 Consider who, what, when and where

Remove the legend from the chart
 Not needed when there is only one series

Source – add in text box
 Insert – Text Box – Draw text box on the
chart and type in source
 If not source give type “Unknown”

Apply a theme if you wish
Make Your Chart More
Readable


XY Graphs often only
take up a small range
of values
If all data points
located in a central
area on the graph
 Adjust y-axis so
values start at or
just below the
lowest data point
value
•Right-click on y-axis
•Choose Format axis
•Adjust Minimum value
The Result…
Solstice Theme applied to this chart
What’s the Story?

XY (Line) Graphs usually tell a story about the data

Analysis should carefully describe what the graph is
saying

Start the “story” from the left and move to the right

Be sure to include the high point and the low point
as well as anything that is interesting or unexpected

Write a well-written paragraph telling the “story”
Describing your graph
In a paragraph, point out what you want the
reader to know about the graph
 Examples:

“In the Annual Averages of Lake Michigan/Lake
Huron Water Levels chart we find that between
1988 and 1997 water levels in the lakes
increased overall. The high point of the lake
levels occurred in 1997 when the level was
176.98 meters. However, lake levels took a
sharp decline in the following 2 years and
reached their low point in 2003 when the level
was only 175.89 meters. Since 2003 lake levels
have increased slightly but appear to be
declining once again.”
Bar Chart or Column Chart




Very flexible
Used when a
quantitative variable
is associated with
the a categorical
variable
Work well with
limited data
Can compare more
than one series
Note: Be Careful
If you do use a bar chart and have years
along the x-axis
 Be sure the years are in equal intervals.
 Otherwise, you can be guilty of creating
a misleading graph


Let’s try one
 Home Heating Tab
Creating a Column Chart


Select the data
including category
labels and values
Choose Column
Chart
 2-D Clustered column
option

Add Titles and axis
labels
 Layout 9 works well
Labeling the Chart

Title should be descriptive
 Consider who, what, when and where
Both the x-axis and y-axis should be
labeled
 Source – add in text box

 Insert – Text Box – Draw text box on the
chart and type in source
 If not source give type “Unknown”

Apply a theme if you wish
Name Each Series in the legend

To change names
 Click on chart to





activate
Click on Design Tab
Under Data Group –
choose Select Data
Data Series labels
appear on left
Highlight label and
click edit button
Type new series
name in Edit Series
Dialog box
The Result…
Source: US Dept of Energy
Aspect Theme applied to chart
Add the other column of data

Reselect the data to include all 3
columns
The New Result
Source: US Dept. of Energy
Advantages of Multiple Bar Charts
Succinctness
 Can make comparisons within
categories and across categories
 Best used in printed works

 Can be carefully studied
Disadvantages
Can present too much information to
view as part of presentation
 Hard to make a single clear point with
bar charts
 Presenters don’t leave them up long
enough to absorb info fully

Describing a Bar/Column Chart
Usually include high and low values in
graph description
 Not always effective/appropriate with
bar/column charts
 Include top 2 or 3 values instead
 Low value may be insignificant

 Often describes “Other” category
 Not significant in the “story”
Guidelines for Creating an
Effective Graph
1.
What is the purpose of making a graph
from this data?
2.
What type of graph should you make?

Decide on a title and consider the W's
3.

4.
Pie, bar, x-y scatter (line)
(who, what, where and when)
Do you need to include a legend?
Guideline continued…
5.
Add a descriptive x-axis and y-axis label
for bar and xy-scatter graphs
6.
Add percentages for pie charts, 2 decimal
places
7.
Adjust the scale for bar and xy-scatter
graphs (if applicable)
8.
Add source
Can the Graph Stand Alone?

A good graph should be able to stand
alone
 Without any words to tell the reader what
they are looking at

If the reader doesn't understand the
graph without a caption (or story) then
the graph isn't very good
Faulty or Misleading Graphs

Data can be displayed "correctly" yet
gives different messages depending on
how it is displayed
Y-axis Scale Effects
Most common way to create a
misleading graph
 Y-axis scale should begin at 0
 Not always the case
 Can work in favor of the one distributing
the graph

Bad Chart Examples

What’s wrong with this chart
Another Bad
Example –
Misleading
Graph
Graph appeared in
Chicago Tribune and
on billboards along
the Kennedy
Expressway