This study addresses the problem of individual differences in solving simple addition problems by comparing the result of group to individual data. We found that if the group data are better explained by the currently dominant model (retrieval of arithmetic facts from memory), individual data are explained by different models at the level of the process used.
"Individual Differences in Cognitive Addition,"
The Psychological Record: Vol. 48
, Article 8.
Available at: http://opensiuc.lib.siu.edu/tpr/vol48/iss2/8