# Graphing - PowerPoint PPT Presentation

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Graphing Types of Graphs Pie Charts XY Graphs Bar Charts What type of graph to use? Pie Charts Limited in their applicability Can only be used when you have a quantitative variable associated with a list of categories where BOTH the categories and the quantities each add up to a WHOLE

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Graphing

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## Graphing

• Pie Charts

• XY Graphs

• Bar Charts

### What type of graph to use?

• Pie Charts

• Limited in their applicability

• Can only be used when you have a quantitative variable associated with a list of categories where BOTH the categories and the quantities each add up to a WHOLE

• The categories must be disjoint

• Most common error – using a pie chart on a set of categories that do not make a whole & to use a pie chart when the categories overlap

• Do not include the total in your pie chart

### What type of graph to use?

• XY Graphs

• Should be used when you have “a lot” of data points and the categories along the x-axis are numerical

• Use the XY Scatter type and then choose a graph option with connected data points, usually

• What Excel calls a “line graph” is very confusing and should essentially never be used (Excel “line graph” always treats the x-axis categorically)

### What type of graph to use?

• Bar Charts

• Very flexible

• Can be used whenever there is a quantitative variable associated with the categorical variable

• Great when you have a limited amount of data or when you want to compare more than one series

• If you do use a bar chart and have years along the x-axis, be sure the years are consecutive

### How to make a pie chart

• ../../Excel_Files/EnergyConsumption2005.xls

• Select both the categories and the values

• The graph needs a descriptive title

• The percentages might need to be “increased” to show one or two decimals

### How to make a Bar Chart

• http://qrc.depaul.edu/Excel_Files/HomeHeating.xls

• Main advantage is their succinctness and the ability they afford to make comparisons within categories and across categories

• Best used in printed works so that a view can study them carefully

• Disadvantage is that they sometimes present far too much information to view as part of a presentation

• It is hard to make a single, clear point with them, and presenters tend not to leave them up long enough to absorb the information fully

• People often make bar charts with quantitative data on the x-axis, but they are not careful about the fact that bar charts treats the x-axis categorically

### How to Make an XY Graph

• http://qrc.depaul.edu/Excel_Files/LakeMichiganLevels1988-2000.xls

• Vocabulary: increasing/decreasing, absolute minimum/maximum, relative minimum/maximum, increasing at an increasing rate, decreasing at a decreasing rate, periodic

• Be able to write paragraphs which describe what the graph is saying, generally going from left to right, telling the “story” of the graph

### Guidelines for making an effective Graph

• What is the purpose of making a graph from this data?

• What type of graph should you make?

• Pie

• Bar

• XY scatter (line)

• Decide on a title and consider the Ws (who, what, where, and when)

• Legend: yes or no?

• Descriptive x-axis label (if applicable)

• Descriptive y-axis label (if applicable)

• Scale (if applicable)

• Source

### How to Describe Graphs

• The 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

• In a paragraph describing the graph, you should point out what you want the reader to know about the graph

### Y-Axis Scale Effects

• One of the most common ways graphs can be misleading

• It has become more and more accepted in the media to adjust the y-axis