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Describing Data Visually (Part 2)PowerPoint Presentation

Describing Data Visually (Part 2)

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### Describing Data Visually (Part 2)

Chapter

Scatter Plots

Tables

Pie Charts

Effective Excel Charts

Maps and Pictograms

Deceptive Graphs

McGraw-Hill/Irwin

© 2008 The McGraw-Hill Companies, Inc. All rights reserved.

- A scatter plot shows n pairs of observations as dots (or some other symbol) on an XY graph.

- A starting point for bivariate data analysis.

- Allows observations about the relationship between two variables.

- Answers the question: Is there an association between the two variables and if so, what kind of association?

- Example: Birth Rates and Life Expectancy

- Here is a scatter plot with life expectancy on the X-axis and birth rates on the Y-axis.

- Is there an association between the two variables?

- Is there a cause-and-effect relationship?

- Example: Aircraft Fuel Consumption

- Consider five observations on flight time and fuel consumption for a twin-engine Piper Cheyenne aircraft.

- A causal relationship is assumed since a longer flight would consume more fuel.

- Example: Aircraft Fuel Consumption

- Here is the scatter plot with flight time on the X-axis and fuel use on the Y-axis.

- Is there an association between variables?

Strong association

Moderate association

Little or no association

Scatter Plots

- Degree of Association

- Policy Making

- Scatter plots can be helpful when policy decisions need to be made.

- For example, compare traffic fatalities resulting from crashes per million vehicles sold between 1995 and 1999.

- Do SUV’s create a greater risk to the drivers of both cars?

In Excel, highlight the two data columns, then click on the Chart Wizard icon on the toolbar.

Select the XY (Scatter) option.

- Making a Scatter Plot in Excel

- Click Next and then click the Series tab.

- Excel assumes that the first column contain X-axis values and the second column contains Y-axis values.
- Alternatively, you can specify the data range explicitly for each variable.

Embellished graph

Scatter Plots

- Making a Scatter Plot in Excel

- Click Finish to display a plain scatter plot.

- You can embellish it using Excel’s options.

- Tables are the simplest form of data display.

- A compound table is a table that contains time series data down the columns and variables across the rows.

- Example: School Expenditures

- Arrangement of data is in rows and columns to enhance meaning.

- The data can be viewed by focusing on the time pattern (down the columns) or by comparing the variables (across the rows).

- Example: School Expenditures

- Units of measure are stated in the footnote.
- Note merged headings to group columns.

- Tips for Effective Tables

1. Keep the table simple, consistent with its purpose.- Summary tables go in the main body.- Detailed tables go in an appendix.- In a slide show, main point of table should be clear within 10 seconds, otherwise, break up table.

2. Display the data to be compared in columns.

3. Round off data to 3 or 4 significant digits.

- Tips for Effective Tables

4. Table layout should guide the eye towards the desired comparison.- Use spaces or shading to separate rows or columns.- Use lines sparingly.

5. Keep row and column headings simple yet descriptive.

6. Use a consistent number of decimal digits within a column.- Right-justify or decimal align the data.

- An Oft-Abused Chart

- A pie chart can only convey a general idea of the data.

- Pie charts should be used to portray data which sum to a total (e.g., percent market shares).

- A pie chart should only have a few (i.e., 2 or 3) slices.

- Each slice should be labeled with data values or percents.

Bar Chart

Pie Charts

- An Oft-Abused Chart

- Consider the following charts used to illustrate an article from the Wall Street Journal. Which type is better?

Exploded Pie Chart

Pie Charts

- Pie Chart Options

- Exploded and 3-D pie charts add strong visual impact but slices are hard to assess.

- Common Errors in Pie Chart Usage

- Pie charts can only convey a general idea of the data values.

- Pie charts are ineffective when they have too many slices.

- Pie chart data must represent parts of a whole (e.g., percent market share).

- Effective visual displays- help you get your point across- are persuasive- help you see facts more clearly- help you make better decisions- make your business report stand out- increase your reputation- make you a more desirable employee

- Easily learned, Excel is widely used because of its excellent graphics capabilities.

Effective Excel Charts plot.

- Chart Wizard

- Click on the Chart Wizard icon on the toolbar to open a sequence of pop-up menus to guide you through the steps of creating a chart.

- Step 1: Select the Chart type and then click Next.

Effective Excel Charts plot.

- Chart Wizard

- Step 2: Add labels for years on the X-axis by selecting a data range (B4:B13). Click Next.

Effective Excel Charts plot.

- Chart Wizard

- Step 3: Embellish the chart by adding a title, axis labels, adjusting the gridlines or appending a data table to the graph by clicking on the appropriate tab.

Effective Excel Charts plot.

- Embellished Charts

- Charts created in Excel can be edited to:

- Improve the titles (main, X-axis, Y-axis).

- Change the axis scales (minimum, maximum, demarcations).

- Display the data values (on the top of each bar).

Effective Excel Charts plot.

- Embellished Charts

- Charts created in Excel can be edited to:

- Add a data table underneath the graph.

Effective Excel Charts plot.

- Embellished Charts

- Charts created in Excel can be edited to:

- Change color or patterns in the plot or chart areas.

Effective Excel Charts plot.

- Embellished Charts

- Charts created in Excel can be edited to:

- Format the decimals (on the axes or data labels).

- Edit the gridlines (color, dotted or solid, patterns).

Effective Excel Charts plot.

- Embellished Charts

- Charts created in Excel can be edited to:

- Alter the appearance of the bars (color, pattern, gap width).

Effective Excel Charts plot.

- Embellished Charts

- To alter a chart’s appearance, click on any chart object and then right-click to see a menu of properties that you can change.

- For example, right-click on the Y-axis scale and choose Format Axis.

Over-embellished chart plot.

Embellished bar chart

Effective Excel Charts

- Embellished Charts

- Be careful about over-embellishing your charts.

Area (mountain) chart plot.

Multiple bar chart

Effective Excel Charts

- Embellished Charts

- Excel offers many other types of specialized charts.

Effective Excel Charts plot.

- Embellished Charts

- Other specialized Excel charts:

- Bubble chart displays three variables on a 2-dimensional scatter plot.

- Note: bubble size is proportional to third variable.

Data from http://peltiertech.com/Excel/ChartsHowTo/HowToBubble.html

Effective Excel Charts plot.

- Embellished Charts

- Other specialized Excel charts:

- Stock chart for high/low/close stock prices.

Data from

http://finance.yahoo.com

Effective Excel Charts plot.

- Embellished Charts

- Other specialized Excel charts:

- Radar (or Spider) chart compares individual performance against abenchmark.

- Caution, data may be distorted by emphasized areas.

Maps and Pictograms plot.

- Spatial Variation and GIS

- Maps can be used for displaying many kinds of data.

- Appropriate when patterns of variation across space are of interest.

- Self-explanatory and revealing.

- Assess patterns based on geography.

- GIS (geographic information systems) combines statistics, geography and graphics.

Maps and Pictograms plot.

- Pictograms

- A visual display in which data values are replaced by pictures.

Maps and Pictograms plot.

- Pictograms

- Although entertaining, they can create visual distortion. What do you think?

Deceptive Graphs plot.

- Error 1: Nonzero Origin

- A nonzero origin will exaggerate the trend.

Correct

Deceptive

Deceptive Graphs plot.

- Error 2: Elastic Graph Proportions

- Keep the aspect ratio (width/height) below 2.00 so as not to exaggerate the graph. By default, Excel uses an aspect ratio of 1.8.

Correct

Deceptive

Deceptive Graphs plot.

- Error 3: Dramatic Title

- Keep short and grab readers attention.

- Error 4: Distracting Pictures

- Avoid so as not to distract readers or impart an emotional slant.

- Error 5: Authority Figures

- Can use pictures of authority figures to impart credibility to self-serving commercial claims.

Deceptive Graphs plot.

- Error 6: 3-D and Rotated Graphs

- Can make trends appear to dwindle into the distance or loom towards you.

Correct

Deceptive

Deceptive Graphs plot.

- Error 7: Missing Axis Demarcations

- If tick marks are missing, you cannot identify individual data values.

- Error 8: Missing Measurement Units or Definitions

- Missing or unclear units of measurement can render a chart useless.

- Error 9: Vague Source

- May indicate lost citation, unknown source, or mixed data sources. Use complete source citations.

Deceptive Graphs plot.

- Error 10: Complex Graphs

- Avoid if possible. Keep your main objective in mind. If necessary, break graph into smaller parts.

Deceptive Graphs plot.

- Error 11: Gratuitous Effects

- Avoid too many annoying special effects when using slide shows.

- Error 12: Estimated Data

- Estimated points should be noted when used or avoided if possible.

Deceptive Graphs plot.

- Error 13: Area Trick

- As figure height increases, so does width, distorting the area.

Deceptive

Correct

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