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Table Of Contents
Data Analysis Using SQL and Excel - Second Edition
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How good is the best-fit line? Understanding how well a model works can be as important as building the model in the first place. Scatter plots of some data look a lot like a line; in such cases, the best-fit line fits the data quite well. In other cases, the data looks like a big blob, and the best-fit line is not very descriptive. The R2 value provides a measure to distinguish these situations.
R2 measures how well the best-fit line fits the data. When the line does not fit the data at all, the value is zero. When the line is a perfect fit, the value is one.
The best way to understand this measure is to see it in action. Figure 12-92 value of 0.9; the two on the bottom have an R2 value of 0.1. The two on the left have positive correlation, and the two on the right have negative correlation.
Figure 12.9: The four examples here show the different scenarios of positive and negative correlation among the data points, and examples with...
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