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# 数据科学代写|经济统计代写Economic Statistics代考|ECON121 Bar Charts and Pie Charts

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## 数据科学代写|经济统计代写Economic Statistics代考|Bar Charts and Pie Charts

A bar chart is a graphical display for depicting categorical data summarized in a frequency, relative frequency, or percent frequency distribution. On one axis of the chart (usually the horizontal axis), we specify the labels that are used for the classes (categories). A frequency, relative frequency, or percent frequency scale can be used for the other axis of the chart (usually the vertical axis). Then, using a bar of fixed width drawn above each class label, we extend the length of the bar until we reach the frequency, relative frequency, or percent frequency of the class. For categorical data, the bars should be separated to emphasize the fact that each category is separate. Figure $2.1$ shows a bar chart of the frequency distribution for the 50 soft drink purchases. Note how the graphical display shows Coca-Cola, Pepsi, and Diet Coke to be the most preferred brands. We can make the brand preferences even more obvious by creating a sorted bar chart as shown in Figure 2.2. Here, we sort the soft drink categories: highest frequency on the left and lowest frequency on the right.

The pie chart provides another graphical display for presenting relative frequency and percent frequency distributions for categorical data. To construct a pie chart, we first draw a circle to represent all the data. Then we use the relative frequencies to subdivide the circle into sectors, or parts, that correspond to the relative frequency for each class. For example, because a circle contains 360 degrees and Coca-Cola shows a relative frequency of $.38$, the sector of the pie chart labeled Coca-Cola consists of $.38(360)=136.8$ degrees. The sector of the pie chart labeled Diet Coke consists of $.16(360)=57.6$ degrees. Similar calculations for the other classes yield the pie chart in Figure 2.3. The numerical values shown for each sector can be frequencies, relative frequencies, or percent frequencies. Although pie charts are common ways of visualizing data, many data visualization experts do not recommend their use because people have difficulty perceiving differences in area. In most cases, a bar chart is superior to a pie chart for displaying categorical data.
Numerous options involving the use of colors, shading, legends, text font, and three-dimensional perspectives are available to enhance the visual appearance of bar and pie charts. However, one must be careful not to overuse these options because they may not enhance the usefulness of the chart. For instance, consider the three-dimensional pie chart for the soft drink data shown in Figure 2.4. Compare it to the charts shown in Figures 2.1-2.3. The three-dimensional perspective shown in Figure $2.4$ adds no new understanding. The use of a legend in Figure $2.4$ also forces your eyes to shift back and forth between the key and the chart. Most readers find the sorted bar chart in Figure $2.2$ much easier to interpret because it is obvious which soft drinks have the highest frequencies.

## 数据科学代写|经济统计代写Economic Statistics代考|Frequency Distribution

As defined in Section 2.1, a frequency distribution is a tabular summary of data showing the number (frequency) of observations in each of several nonoverlapping categories or classes. This definition holds for quantitative as well as categorical data. However, with quantitative data we must be more careful in defining the nonoverlapping classes to be used in the frequency distribution.

For example, consider the quantitative data in Table 2.4. These data show the time in days required to complete year-end audits for a sample of 20 clients of Sanderson and Clifford, a small public accounting firm. The three steps necessary to define the classes for a frequency distribution with quantitative data are

1. Determine the number of nonoverlapping classes.
2. Determine the width of each class.
3. Determine the class limits.

## 数据科学代写|经济统计代写ECONOMIC STATISTICS代考|BAR CHARTS AND PIE CHARTS

$.38(360)=136.8$ 度。饼图中标有健怡可乐的部分包括. $16(360)=57.6$ 度。其他类的类似计算得出图 $2.3$ 中的饼图。为每个扇区显示的数值可以是频率、相对频

1. 确定每个类的宽度。
2. 确定类限制。

## Matlab代写

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