Measure to compare true observed response with predicted response in regression tasks.

## Arguments

- truth
(

`numeric()`

)

True (observed) values. Must have the same length as`response`

.- response
(

`numeric()`

)

Predicted response values. Must have the same length as`truth`

.- na_value
(

`numeric(1)`

)

Value that should be returned if the measure is not defined for the input (as described in the note). Default is`NaN`

.- ...
(

`any`

)

Additional arguments. Currently ignored.

## Details

R Squared is defined as $$
1 - \frac{\sum_{i=1}^n \left( t_i - r_i \right)^2}{\sum_{i=1}^n \left( t_i - \bar{t} \right)^2}.
$$
Also known as coefficient of determination or explained variation.
Subtracts the `rse()`

from 1, hence it compares the squared error of
the predictions relative to a naive model predicting the mean.

This measure is undefined for constant \(t\).