Is self-identity an independent determinant of intention in the Reasoned Action Approach?

This thesis investigated whether self-identity is a variable within the Reasoned Action Approach, a theoretical model about decision making. The Reasoned Action Approach is one of the most used models for understanding behavior in health psychology and is used in interventions and health programs. Therefore, an addition to that model has an effect on a lot of research which can benefit from having an additional variable that can be used in a wide range of behaviors. Three studies have been done in the thesis. In the first study thirty years of studies about self-identity within Reasoned Action have been studied and resulted in a new definition and a new self-identity scale. In the two following up studies that self-identity scale was tested and it was found that self-identity indeed is an additional variable and thus should be included. Researchers and implementors, for example in the healthcare, will find a new, clear definition of what self-identity is, how to measure it and some suggestions for implementation within this thesis.