Chapter 5, Correlations and the Importance of Variables

1. You can, for example, build a diagram with the categorical values on the x axis and the numerical values on the y axis; any correlation would be clear from this diagram.
2. It should be easy for the reader to build diagrams and understand the relationship between variables.
3. No. It means that when a variable increases, the other variable decreases.
4. This formatting was used in Chapter 6, Data Mining Models in Excel Hands-On Examples.
5. We calculated the Squared Error (SSE) as ([@mpg]-[@prediction])^2. The other sum we need is SST = ([@mpg]-average([@prediction]))^2. Then, we calculate R² = 1-SSE/SST.
6. You can try using an exponential function (EXP()) or another function with a similar shape. The R² value will probably still be far from 1, since the dispersion in the data is very high.

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