^May, D. R., Gilson, R. L., & Harter, L. M. (2004). The psychological conditions of meaningfulness, safety and availability and the engagement of the human spirit at work. Journal of Occupational and Organizational Psychology, 77, 11-37
^Schaufeli, W.B., Salanova, M., González-Romá, V., & Bakker, A. B. (2002). The measurement of Engagement and burnout: A confirmative analytic approach. Journal of Happiness Studies, 3, 71-92
^Schaufeli, W.B., Bakker, A.B. & Salanova, M. (2006). The measurement of work engagement with a short questionnaire: A cross-national study. Educational and Psychological Measurement, 66, 701-716
^Schaufeli, W.B., Martínez, I., Marques Pinto, A. Salanova, M. & Bakker, A.B. (2002). Burnout and engagement in university students: A cross national study. Journal of Cross- Cultural Psychology, 33, 464-481
^For an overview see: Schaufeli, W.B. 2007 pp. 135-177