Phi Coefficient Formula

[santiviquez]

We are missing the formula. It should be color-coded and described with arrows following the standards of other formulas present in the book.

Here it is standard Accuracy as an example:

[elcapo]

Hi @santiviquez,

The formula that appears in the Wikipedia article about the Phi coefficient, in other words, this:

$${\displaystyle {\upphi}={\frac {{\mathit {TP}}\times {\mathit {TN}}-{\mathit {FP}}\times {\mathit {FN}}}{\sqrt {({\mathit {TP}}+{\mathit {FP}})({\mathit {TP}}+{\mathit {FN}})({\mathit {TN}}+{\mathit {FP}})({\mathit {TN}}+{\mathit {FN}})}}}}$$

Is correct?

If so, I'd be happy to contribute by adding it.

[santiviquez]

Hi @elcapo that's correct. But I've just realized that this issue is duplicated since phi-coefficient is exactly the same as the Matthew’s Correlation Coefficient and that one has already been solved under this PR #168

But feel free to take another one.