From SuperMemo Help
Jump to navigation Jump to search
decline of O-Factors with successive repetitions can be approximated with a power curve that begins at O-Factor that equals A-Factor. D-Factors are no longer used in SuperMemo Algorithm. When a power regression is used to compute O-Factors on the basis of R-Factors for successive repetitions in a single A-Factor category, the decay constant of the resulting function is called a D-Factor. You can see individual D-Factors for all A-Factors in Toolkit : Statistics : Analysis : Graphs : D-Factor vs. A-Factor. The larger the D-Factor the faster the decline of O-Factors with each repetition. This means that large D-Factors imply more frequent repetitions in a given difficulty category. Naturally, over time, D-Factors tend to be lower for easy item categories (unless O-Factors hit their minimum value of 1.2 for very difficult items). D in D-Factor stands for decay (it is a decay constant of the negative power function)