Colligan, R. C., Offord, K. P., Malinchoc, M., Schulman, P., & al., et. (1994). CAVEing the MMPI for an optimism-pessimism scale: Seligman’s attributional model and the assessment of explanatory style. Journal of Clinical Psychology, 50(1), 71–95. John Wiley \& Sons Inc, US,  http://www.wiley.com