Harker, L., Keltner, D. (2001), 'Expressions of positive emotion in women's college yearbook pictures and their relationship to personality and life outcomes across adulthood', Journal of Personality and Social Psychology, 80(1), 112. Результаты других исследований можно найти здесь: Harter, S. (2012), The Construction of The Self: Developmental and Sociocultural Foundations (2nd edition), New York: The Guilford Press.