The Investment Model Scale (IMS): further studies on construct validation and development of a shorter version (IMS-S).

The Investment Model (IM; Rusbult, 1980, 1983) has been widely used to study the development and maintenance of romantic relationships. Its components--satisfaction, quality of alternatives, investment size and commitment--are operationalized in the Investment Model Scale (IMS; Rusbult, Martz, & Agnew, 1998). Given its importance for personal relationships literature, this article presents the adaptation and validation of the IMS to Portugal, and the development and validation of a shorter version, the IMS-S. A confirmatory factor analysis replicates the IMS's original four factors structure. A similar structure was found for the IMS-S. For both versions, results show the instruments to have validity and good reliability. Results are discussed considering the scales' importance for studying romantic relationships.