In probabilistic classification problems, the label space $\mathbf{Y}$ is finite and Forecaster is required to output a probability measure on $\mathbf{Y}$. In binary classification problems, the size of $\mathbf{Y}$ is 2; usually, $\mathbf{Y}=\{0,1\}$ or $\mathbf{Y}=\{-1,1\}$, and a forecast can be interpreted as a number in the interval ${[0,1]}$ (the predicted probability of the outcome 1).