Measure to compare true observed labels with predicted labels in binary classification tasks.

## Arguments

- truth
(

`factor()`

)

True (observed) labels. Must have the exactly same two levels and the same length as`response`

.- response
(

`factor()`

)

Predicted response labels. Must have the exactly same two levels and the same length as`truth`

.- positive
(

`character(1))`

Name of the positive class.- ...
(

`any`

)

Additional arguments. Currently ignored.

## Details

The Matthews Correlation Coefficient is defined as $$ \frac{\mathrm{TP} \cdot \mathrm{TN} - \mathrm{FP} \cdot \mathrm{FN}}{\sqrt{(\mathrm{TP} + \mathrm{FP}) (\mathrm{TP} + \mathrm{FN}) (\mathrm{TN} + \mathrm{FP}) (\mathrm{TN} + \mathrm{FN})}}. $$

This above formula is undefined if any of the four sums in the denominator is 0. The denominator is then set to 1.

## References

Matthews BW (1975).
“Comparison of the predicted and observed secondary structure of T4 phage lysozyme.”
*Biochimica et Biophysica Acta (BBA) - Protein Structure*, **405**(2), 442--451.
doi:10.1016/0005-2795(75)90109-9
.