This dissertation is concerned with the role of regret aversion in decision making. Specifically, it examines how regret aversion influences decision process, choice, and post-decisional behaviors and feelings. Chapter 1 provides an overview of the past empirical findings and theorizing on regret aversion. Chapter 2 examines whether regret aversion leads to a stronger or weaker preference for so-called reason-based choices (cf., Shafir, Simonson, & Tversky, 1993), or options that are more easily justifiable. Specifically, four experiments test whether four well-known reason-based choice effects are amplified or attenuated when regret is made salient. These effects are the asymmetric dominance effect, the compromise effect, the select/reject effect, and the most important attribute effect. Chapter 3 reports on five experiments that examine whether regret aversion leads decision makers to engage in more careful decision processing as suggested by Janis and Mann (1977). It extends the study of regret aversion from choice behavior to decision processing. Chapter 4 studies the effects of regret aversion in repeated decisions. Specifically, it examines experimentally how decision makers handle the trade off between seeking feedback on foregone options that may facilitate learning and better decision making in future decisions, and avoiding feedback on foregone options as such feedback may cause feelings of regret. Chapter 5 summarizes the contributions of this dissertation and concludes.

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Det senaste decenniet har användandet av sociala medier exploderat och blivit en plattformdär information och tips om aktier och investeringar delas ut. Unga personer är de störstaanvändarna av sociala medier, och tidigare studier visar att denna åldersgrupp uppvisar ettmer riskfyllt beteende på aktiemarknaden. Syftet med denna studie var således att undersökahuruvida det finns ett samband mellan aktivitet på sociala medier och riskbenägenhet. Vidareundersöktes om tre variabler - överdrivet självförtroende, ångeraversion och kognitivdissonans - hade en medierande effekt i sambandet mellan aktivitet på sociala medier ochriskbenägenhet. En kvantitativ metod med en enkätstudie användes för studiensdatainsamling. Statistiska mått, däribland regressionsanalys och medieringsanalys, användesför att besvara forskningsfrågan. Resultaten visade att sociala medier har en statistisktsignifikant effekt på riskbenägenhet på aktiemarknaden, och att överdrivet självförtroende haren statistiskt signifikant medierande effekt på relationen. Det fanns inga belägg ellerindikationer på att kognitiv dissonans och ångeraversion har en medierande effekt.Sammanfattningsvis visade studien att aktivitet på sociala medier i investeringssyfte kanbidra till ökad riskbenägenhet, och att överdrivet självförtroende har en viktig roll sommedierande variabel i förhållandet. / The last decade, the use of social media has escalated and become a platform whereinformation and tips about stocks and investments are shared. Young individuals aregenerally the most frequent users of social media, and studies also show that the same agegroup displays a more risk-prone behavior in financial markets. Therefore, the purpose of thisstudy was to examine the potential effect of social media activity on risk propensity on thestock market. Furthermore, the study investigated whether the three variables -overconfidence, regret aversion, and cognitive dissonance - could be classified as a mediatingvariable between social media activity and risk propensity. The study was conducted using aquantitative method, employing a survey, where 130 people responded. Statistical measuressuch as regression analysis and mediation analysis were used to answer the research question.The results showed that social media has a statistically significant effect on risk propensity onthe stock market, and that overconfidence has a statistically significant mediating effect onthe relationship. There was no evidence or indication that cognitive dissonance or regretaversion has a mediating effect. In summary, the study demonstrated that use of social mediain investment purposes can increase risk willingness, and that overconfidence plays animportant role as a mediating variable in this relationship.