643 The Impact of Unfair Treatment on Depressive Mood: The Moderating Role of Self-Esteem Level and Self-Esteem Instability Laurenz L. Meier Norbert K. Semmer Jörg Hupfeld University of Bern, Switzerland anxiety and depression (e.g., Niedhammer, David, & Degioanni, 2006; Schulz et al. 2006), and daily hassles are related to negative affect, low self-esteem, and depression on a daily level (e.g., Bolger, DeLongis, Kessler, & Schilling, 1989; Nezlek & Plesko, 2001, 2003; Zeigler- Hill & Showers, 2007). Chronic stressors and negative events vary in the degree of their severity. Events involving interpersonal rejection may be especially aversive because they undermine the fundamental need to belong to significant groups and to maintain good interpersonal relationships (Baumeister & Leary, 1995). Previous research has shown that rejection is likely to compromise people’s well-being (see Leary, 2001; Williams, 2007). Interpersonal rejection can take many forms and occurs in different social contexts, such as rejection by a romantic partner, bullying at school, exclusion from a sport club, or unfair treatment at the workplace. Unfair treatment at the workplace can have different faces. Generally, researchers have identified three types of (un)fairness (see Colquitt, Greenberg, & Zapata- Phelan, 2005): first, fairness of outcomes (distributive fairness); second, fairness of procedures used for allocation decisions (procedural fairness); and third, fairness of interpersonal treatment during procedures Authors’ Note: Laurenz L. Meier and Norbert K. Semmer are affili- ated with the Swiss Centre for Affective Sciences. We thank Ulrich Orth, Sven Gross, Fabienne T. Amstad, Martial Berset, Viviane Gisler, and Colm O’Mahony for their helpful comments on an earlier version of this article and Markus Hausammann, Christian Rohr, and David Schönenberger for their help during data collection. Correspondence concerning this article should be addressed to Laurenz L. Meier, Department of Psychology, University of Bern, Muesmattstrasse 45, CH-3000 Bern 9, Switzerland; e-mail: laurenz.meier@psy.unibe.ch. PSPB, Vol. 35 No. 5, May 2009 643-655 DOI: 10.1177/0146167208331337 © 2009 by the Society for Personality and Social Psychology, Inc. This research examines the moderating roles of self-es- teem level and self-esteem instability in the relationship between perceived unfair treatment and depressive mood. Based on the assumption that unfairness is a threat to one’s social standing and self-esteem, the authors proposed that individuals with highly fragile self-esteem (i.e., the combination of unstable and high self-esteem) react more strongly when experiencing unfair treatment. This hypothesis was tested in a real- world setting using cross-sectional and diary data of 101 employees. As expected, unfair treatment was related to depressive mood among individuals with unstable high self-esteem but not among individuals with stable high self-esteem. This pattern of results held for both cross-sectional and diary data. In contrast, unfairness was not related to depressive mood among individuals with unstable low self-esteem. Keywords: self-esteem; self-esteem instability; fairness; depres- sive mood R esearch suggests that people are highly concerned about how fairly they are treated by others and that they react with impaired well-being to perceived unfairness (Folger & Cropanzano, 1998). However, individuals differ in the degree to which they are reac- tive to unfair events (De Cremer, 2002a). This study focuses on individual differences by examining the mod- erating effects of self-esteem level and instability. Unfair treatment can be regarded as a stressor. Stressors, both in terms of chronic conditions and in terms of negative daily events, affect psychological adjustment on a chronic level as well as on a daily level. For example, enduring stressors like the experience of workplace bullying and discrimination are related to