Exploring Data in One Dimension

Bar Charts

Interval variables contain values distributed over a continuous range. For example, in Figure 4.2 baseball players' salaries are stored in SALARY, an interval variable. To create a bar chart of players' salaries, follow these steps.

Select SALARY in the data window.

Scroll all the way to the right to find the SALARY variable. Point and click on the variable name.

Figure 4.2: Selecting the SALARY Variable

Choose Histogram/Bar Chart ( Y ) from the Analyze menu.

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Figure 4.3: Creating a Bar Chart

This creates a bar chart, as shown in Figure 4.4.

Figure 4.4: Bar Chart

Point and click on any bar.

This labels the bar with its frequency and selects all the observations in the bar.

Figure 4.5: Clicking on a Bar

Notice that the observations are selected in the data window as well as in the bar chart window. Windows in SAS/INSIGHT software are just different views of the same data, so observations you select in one window are selected in all other windows.

Figure 4.6: Selecting Observations in Multiple Windows

From this bar chart, you can see that the distribution of players' salaries is skewed to the right, with a few players earning high salaries. To find the number of players making the highest salaries, you can label all bars with their heights.

Click on the menu button in the bottom left corner of the chart.

This displays the bar chart pop-up menu in Figure 4.7. Click on Values.

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Figure 4.7: Bar Chart Pop-up Menu.

This toggles the display of values for all bar heights. There are three players making salaries above $2,000,000.

Figure 4.8: Bar Heights

It would be interesting to determine whether salaries differ in the American and National leagues. To compare the distribution of salaries from both leagues, follow these steps.

Select LEAGUE in the data window.

Figure 4.9: Selecting LEAGUE

Note that LEAGUE is a nominal variable. Nominal variables contain a discrete set of values. For example, LEAGUE contains only two values, American and National, for the American and National leagues.

Choose Histogram/Bar Chart ( Y ) from the Analyze menu.

From the bar chart in Figure 4.10 you can see that the BASEBALL data set has more observations from the American League.

Figure 4.10: Bar Chart of LEAGUE

Select Values from the bar chart pop-up menu in the new bar chart.

This displays the frequencies for each of the leagues at the top of the bars on the bar chart.

Figure 4.11: Bar Chart with Frequency Values

Arrange the windows so you can see both bar charts.

Click on the bar that represents the American League.

This selects all observations for players in the American League.

Figure 4.12: Selecting American League Observations

Click on the bar that represents the National League.

This selects all observations for players in the National League.

Figure 4.13: Selecting National League Observations

Both leagues have a broad distribution of SALARY with most players earning below $1,000,000 and a few earning much more.

You can examine the distributions in more detail by creating box plots.