Example 6: A labor union might produce this graph to show the difference between the average manager salary and the average worker salary. The average manager salary is manager salary is 4 times as large twice as high as the average as the worker salary. The area worker salary as in a bar graph, needs to accurately portray the but the image is also twice as relationship, otherwise we will wide. That makes it look like the have a perceptual distortion. Misleading Scale Another type of distortion in bar charts results from setting the baseline to a value other than zero. The baseline is the bottom of the vertical axis, representing the least number of cases that could have occurred in a category. Normally, this number should be zero. Example 7: Compare the two graphs below showing support for same-sex marriage rights from a poll taken in December, 2008. At a glance, the two graphs suggest very different stories. The second graph makes it look like more than three times as many people oppose marriage rights as support them. But when we look at the scale we can see that the difference is about 12%. By not starting at zero the difference looks enlarged. Stacked Bar Graphs Another type of graph that can be hard to read and sometimes misleading is a stacked bar graph. In a stacked bar graph, the values we are comparing are stacked on top of each other vertically. Example 8: The lists college Student Student expenses for two different students Expense 1 2 and we want to compare them. A Rent $500 $650 stacked bar graph shows the Food $125 $125 expenses stacked vertically, but we Tuition $1750 $1450 are interested in the differences, not Books $325 $275 the totals. Misc $100 $175 It would be much easier to interpret the differences in a side-by-side bar chart.
Example 6: A labor union might produce this graph to show the difference between the average manager salary and the average worker salary. The average manager salary is twice as high as the average worker salary as in a bar graph, but the image is also twice as wide. That makes it look like the manager salary is 4 times as large as the worker salary. The area needs to accurately portray the relationship, otherwise we will have a perceptual distortion. Misleading Scale Another type of distortion in bar charts results from setting the baseline to a value other than zero. The baseline is the bottom of the vertical axis, representing the least number of cases that could have occurred in a category. Normally, this number should be zero. Example 7: Compare the two graphs below showing support for same-sex marriage rights from a poll taken in December, 2008. At a glance, the two graphs suggest very different stories. The second graph makes it look like more than three times as many people oppose marriage rights as support them. But when we look at the scale we can see that the difference is about 12%. By not starting at zero the difference looks enlarged. Stacked Bar Graphs Another type of graph that can be hard to read and sometimes misleading is a stacked bar graph. In a stacked bar graph, the values we are comparing are stacked on top of each other vertically. Example 8: The lists college expenses for two different students and we want to compare them. A stacked bar graph shows the expenses stacked vertically, but we are interested in the differences, not the totals. Expense Student 1 Student 2 Rent $500 $650 Food $125 $125 Tuition $1750 $1450 Books $325 $275 Misc $100 $175 It would be much easier to interpret the differences in a side-by-side bar chart.
Chapter3-Statistics9-7-18.docx