D. Nießen, K. Groskurth, C. J. Kemper, B. Rammstedt, and C. M. Lechner, “The Optimism–Pessimism Short Scale–2 (SOP2): A Comprehensive Validation of the English-Language Adaptation”, Meas Instrum Soc Sci, vol. 4, no. 1, p. Article e11067, Jan. 2022.