24
Ron Gutman (2011), ‘The hidden power of smiling’, TED talk, .
25
Ernest L. Abel and Michael L. Kruger (2010), ‘Smile Intensity in Photographs Predicts Longevity’, Psychological Science, volume 21, issue 4, pp. 542–544.
26
M. E. P. Seligman and S. F. Maier (1967), ‘Failure to escape traumatic shock’, Journal of Experimental Psychology, volume 74, pp. 1–9.
27
Robert A. Karasek, Jr. (1979), ‘Job Demands, Job Decision Latitude, and Mental Strain: Implications for Job Redesign’, Administrative Science Quarterly, volume 24, number 2, pp. 285–308.
