A-Factor

A-Factor (for absolute difficulty factor) is a number that reflects item difficulty in Algorithms SM-8, SM-11 and SM-15. In SuperMemo 18, A-Factor is a number associated with every element in the collection. A-Factors help determine how much intervals increase in the learning process. The higher the A-Factor, the faster the interval increase. You can see A-Factors in the Element data window.

For items: A-Factors correspond with item difficulty. In most cases, the higher the A-Factor the easier the item. The most difficult items usually have A-Factors equal to 1.2. For items, A-Factor is defined as the quotient of the second optimum interval and the first optimum interval used in repetitions in Algorithm SM-15.

For topics and tasks: A-Factors modulate topic priority (by affecting the frequency of exposition). For topics and tasks, A-Factor is interpreted as the number by which the current interval should be multiplied to get the value of the next interval (as it was the case with E-Factors in the early versions of SuperMemo).

For origins of A-Factors, see: First data-driven spaced repetition algorithm: Algorithm SM-8

This glossary entry is used to explain SuperMemo, a pioneer of spaced repetition software since 1987