Memory variability is due to the contribution of recollection and familiarity, not to encoding variability.

It is well established that the memory strength of studied items is more variable than the strength of new items on tests of recognition memory, but the reason why this occurs is poorly understood. One account for this old item variance effect is based on single-process theory, which proposes that this effect is due to variability in how well items are initially encoded into memory (i.e., the encoding variability account). In contrast, dual-process theory argues that old items are more variable because they are influenced by both recollection and familiarity, whereas recognition of new items relies primarily on familiarity. The present study shows that increasing encoding variability did not increase old item variance and that old item variance is directly related to the contribution of recollection. These results indicate that old item memory variability is due to the relative contribution of recollection and familiarity.