Concept drift

A model suffers a concept drift if the very meaning of the modeling problem changes: for example, the criteria to diagnose an illness change.

• $P(y_s|x_s)\ne P(y_t|x_y)$, when $X\to Y$
• $P(x_s|y_s)\ne P(x_t|y_t)$, when $Y\to X$