However, when you are interested in the way that two numeric variables are related, you are asking a different sort of question, and you use a different sort of statistical analysis. The relationship between the two variables differs fundamentally from those discussed earlier in this chapter, where the emphasis is placed on the sum or average of a numeric variable, such as number of vehicles, according to the category of a nominal variable, such as make of car. In Figure 1.8, for example, you can see the relationship between a person’s height and weight: Generally, the greater the height, the greater the weight. Chapter 4, “How Variables Move Jointly: Correlation,” goes into considerable detail about this sort of relationship. The overall pattern of the markers can tell you quite a bit about the relationship between the variables, as expressed in each record’s measurement. The markers in an XY chart show where a particular person or object falls on each of two numeric variables. For the most part, this book opts for the brevity of XY chart, and when you see that term you can be confident it’s the same as an XY (Scatter) chart.
In its 2007 version, Excel started referring to it as an XY chart in some places, as a Scatter chart in others, and as an XY (Scatter) chart in still others. Since the 1990s at least, Excel has called this sort of chart an XY (Scatter) chart.
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