Making and Interpreting Graphs

Making and Interpreting Graphs

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Making and Interpreting Graphs

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1. Week 4 LSP 120 Joanna Deszcz Making and Interpreting Graphs

2. 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

3. 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

4. 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

5. 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

6. 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”

7. Chart Themes • Found on Page Layout Tab • Slide mouse over built-in themes • Chart will change to reflect each theme

8. The Result… Flow Theme applied to the chart

9. XY Graphs • Used with a lot of data • X-axis categories are numeric, (often years) • Choose xy graph option with connected data points

10. 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

11. 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

12. 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

13. 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

14. The Result… Solstice Theme applied to this chart

15. 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”

16. 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.”

17. 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

18. 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

19. 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

20. 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

21. 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

22. The Result… Source: US Dept of Energy Aspect Theme applied to chart

23. Add the other column of data • Reselect the data to include all 3 columns

24. The New Result Source: US Dept. of Energy

25. Advantages of Multiple Bar Charts • Succinctness • Can make comparisons within categories and across categories • Best used in printed works • Can be carefully studied

26. 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

27. 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”

28. Guidelines for Creating an Effective Graph • What is the purpose of making a graph from this data? • What type of graph should you make?  • Pie, bar, x-y scatter (line)    • Decide on a title and consider the W's • (who, what, where and when) • Do you need to include a legend?

29. Guideline continued… • Add a descriptive x-axis and y-axis label for bar and xy-scatter graphs • Add percentages for pie charts, 2 decimal places • Adjust the scale for bar and xy-scatter graphs (if applicable) • Add source

30. 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

31. Faulty or Misleading Graphs • Data can be displayed "correctly" yet gives different messages depending on how it is displayed

32. 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

33. Bad Chart Examples • What’s wrong with this chart

34. Another Bad Example – Misleading Graph Graph appeared in Chicago Tribune and on billboards along the Kennedy Expressway