Śliwak, J., and R. P. Bartczuk. “Altruism/Non-Altruism Questionnaire – Short Version: The Revision of the Method Based on Bifactor Analysis”. Journal for Perspectives of Economic Political and Social Integration, vol. 29, no. 1, Dec. 2023, pp. 31-59, doi:10.18290/pepsi-2023-0002.