3.2 Scatter diagrams

A scatter diagram is another way to visualise a quantitative bivariate data set. This is a two-dimensional diagram or graph with one variable on the x-axis (the independent variable) and the other variable on the y-axis (the dependent variable). We then plot the corresponding point on the diagram.

In the next activity, you will learn how to produce a scatter diagram in Excel.

Activity 9: Drawing scatter diagrams

Allow approximately 60 minutes to complete this activity

In this activity you will learn how to make an ungrouped frequency table in Excel, either by watching the screencast or by following the instructions that are given below.

Video 3

Transcript (opens in new window)

Look at the following example, which shows a data set relating to the temperature on days in June, and the number of Pepsi drinks sold in a small shop.

Table 9 Temperature and number of drinks sold

Temperature (X)	12	14	15	17	22	13	20	23
Pepsi (Y)	12	16	16	19	32	10	24	40

Now we draw the scatter diagram (see file: Pepsi data.xlsx). In the example above, temperature is the independent variable and number of Pepsis is the dependent variable, as the sale of Pepsi is affected by changes in the temperature. Hence, we plot temperature on the x-axis and Pepsi on the y-axis.

To find out if there is any relationship between variable X (Temperature) and variable Y (Pepsi), execute the following steps in Excel.

Select the range A1:B9

Figure 25 Spreadsheet of Pepsi sold and Temperature

On the Insert tab, in the Charts group, click the Scatter symbol.

Figure 26 How to select the Scatter symbol

Section of the Scatter type selection menu in Excel

Figure 27 How to select the Scatter chart type

Optional – returning to our example JC Electrics, draw a scatter diagram for Generators

Discussion

Scatter diagram showing the relationship between temperature and Pepsi sales

Figure 28 Temperature versus Pepsi sales

The final image shows the positive relationship between the number of Pepsis sold and the temperature. This shows that as the temperature increases, sales of Pepsi also increase.

For JC Electrics Generators, a scatter diagram for Generators will show as in Figure 28. This presents a slight overall increase in sales, with peaks in sales in quarter 6 with a value of 14, and quarter 10 and 15 with a value of sales of 13 generators, as well as in quarter 21 with a value of 14 and quarter 22 with a value of 15.

Figure 29 Generator sales scatter diagram

OpenLearn - Data analysis: visualisations in Excel
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