Statistics for Dummies by Deborah Jean Rumsey
Authors: Deborah Jean Rumsey
Tags: Reference, Non-Fiction
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the actual "slices" of pizza that correspond to the percentages in the table. What's nice about this display, however, is that it shows the amount of money as well as the percentages that are spent in each area. (By the way, no matter what the total amount of tax dollars is, the percentages showing where the money is allocated don't change; only the dollar amounts do.)
Examining Figure 4-6 , you can see that the biggest slice of your tax dollars go to Social Security (23%), and the second biggest slice goes to national defense (17%). It seems strange, though, that the IRS breaks down certain categories as low as single digits (for example 7% going to Medicaid), but the third highest slice of the pie (or in this case, pizza) actually shows up as "other expenses" (16%).
HEADS UP
Ideally, a pie chart doesn't have too many slices because a large number of slices distracts the reader from the big issues that the pie chart is trying to relay. However, if lumping all of those remaining categories into a category called "other" results in a category that's one of the largest ones in the whole pie chart, readers are left wondering what's included in that slice of pie.
Perhaps you're wondering what those "other expenses" are in the IRS chart. If you probe further on the IRS Web site, the IRS tells you that "other expenses" means "federal employment retirement benefits, payments to farmers, and other activities." This doesn't provide a great deal of additional information, but maybe that's all you really want to know. In fairness to the IRS, I'm sure the details are all spelled out in some neatly filed government report.
Predicting population trends
The U.S. Census Bureau provides many data displays in its reports about the U.S. population. Figure 4-7 shows two pie charts comparing the racial breakdown of the United States in 1995 (actual figures) with the projected racial breakdown in 2050, if current trends continue. You can see that in 1995, about 73.6% of the U.S. population was White, while Blacks made up the second highest group at 12.0%, closely followed by those of Hispanic origin, who comprised 10.2% of the population. (Note that although Hispanics are typically white or black, they are shown here as a separate category, independent of racial background.) The Census Bureau projects that Whites will be a declining share of the total U.S. population in the future, whereas the Hispanic share of the population will grow faster than that of non-Hispanic Blacks. This point is made well using the two pie charts, as opposed to tables simply showing the percentages.
Figure 4-7: Ethnicity trends for the United States.
Evaluating a pie chart
Tip
To taste test a pie chart for statistical correctness:
Check to be sure the percentages add up to 100% or close to it (any round-off error should be very small).
Beware of slices of the pie called "other" that are larger than many of the other slices.
Look for a reported total number of units, so that you can determine how big the pie was before being divided up into the slices that you're looking at.
Putting Statistics on the Table
A table is a data display that presents summary information from a data set in a row-and-column format. Some tables are clear and easy to read; others leave something to be desired. Although a pie chart or a bar graph is usually intended to make one or two points at most, a table can make several points at once (which can be good or bad, depending on the effect this has on the reader).
Statistical information is compiled by researchers not only for their own reports, but also so that others can use the information to do their own research and answer their own questions. Tables are often used in these situations.
Examining birth statistics
The Colorado Department of Public Health and Environment compiles tables on birth statistics for Colorado residents. Table 4-2 shows the number of live births by the sex of the child and the plurality status (single
Examining Figure 4-6 , you can see that the biggest slice of your tax dollars go to Social Security (23%), and the second biggest slice goes to national defense (17%). It seems strange, though, that the IRS breaks down certain categories as low as single digits (for example 7% going to Medicaid), but the third highest slice of the pie (or in this case, pizza) actually shows up as "other expenses" (16%).
HEADS UP
Ideally, a pie chart doesn't have too many slices because a large number of slices distracts the reader from the big issues that the pie chart is trying to relay. However, if lumping all of those remaining categories into a category called "other" results in a category that's one of the largest ones in the whole pie chart, readers are left wondering what's included in that slice of pie.
Perhaps you're wondering what those "other expenses" are in the IRS chart. If you probe further on the IRS Web site, the IRS tells you that "other expenses" means "federal employment retirement benefits, payments to farmers, and other activities." This doesn't provide a great deal of additional information, but maybe that's all you really want to know. In fairness to the IRS, I'm sure the details are all spelled out in some neatly filed government report.
Predicting population trends
The U.S. Census Bureau provides many data displays in its reports about the U.S. population. Figure 4-7 shows two pie charts comparing the racial breakdown of the United States in 1995 (actual figures) with the projected racial breakdown in 2050, if current trends continue. You can see that in 1995, about 73.6% of the U.S. population was White, while Blacks made up the second highest group at 12.0%, closely followed by those of Hispanic origin, who comprised 10.2% of the population. (Note that although Hispanics are typically white or black, they are shown here as a separate category, independent of racial background.) The Census Bureau projects that Whites will be a declining share of the total U.S. population in the future, whereas the Hispanic share of the population will grow faster than that of non-Hispanic Blacks. This point is made well using the two pie charts, as opposed to tables simply showing the percentages.
Figure 4-7: Ethnicity trends for the United States.
Evaluating a pie chart
Tip
To taste test a pie chart for statistical correctness:
Check to be sure the percentages add up to 100% or close to it (any round-off error should be very small).
Beware of slices of the pie called "other" that are larger than many of the other slices.
Look for a reported total number of units, so that you can determine how big the pie was before being divided up into the slices that you're looking at.
Putting Statistics on the Table
A table is a data display that presents summary information from a data set in a row-and-column format. Some tables are clear and easy to read; others leave something to be desired. Although a pie chart or a bar graph is usually intended to make one or two points at most, a table can make several points at once (which can be good or bad, depending on the effect this has on the reader).
Statistical information is compiled by researchers not only for their own reports, but also so that others can use the information to do their own research and answer their own questions. Tables are often used in these situations.
Examining birth statistics
The Colorado Department of Public Health and Environment compiles tables on birth statistics for Colorado residents. Table 4-2 shows the number of live births by the sex of the child and the plurality status (single
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