The investment model of commitment, originally described by Caryl E. Rusbult, is a predictive psychological theory that aims to explain why people remain in relationships.
Its tenants are based primarily on those of interdependence theory, created by Harold Kelley and John Thibaut.
[6] Given that in relationships, there is often an unjustified persistence for people to stay together, it seems as though there must be other things at work besides just satisfaction, and comparison with alternatives.
[7] Given this fact, the investment model describes these three factors, and claims that all of these things add up to a central measure of commitment.
Much has been researched regarding this topic, and evidence points towards the investment model as an accurate predictor of all types of relationship success.
[11][better source needed] Intrinsic investments are commonly referred to as things that are put directly into the relationship that we are in.
In order to test this theory, a longitudinal study was performed in which married participants were mailed a questionnaire to fill out asking various questions about the relationship, regarding satisfaction, investments, and quality of alternatives.
[18] After analysis of the data, it was found that levels of satisfaction, quality of alternatives, and investments all fit with Rusbult's predicted model.
[11] Another study, performed by Rhahgan and Axsom in 2006, attempted to understand if the investment model would be successful in predicting the commitment shown by women in abusive relationships.
The participants included were recruited from a battered women's shelter, and were asked to complete a questionnaire regarding relationships they had in the past.
Using 52 studies and over 11,000 participants, they found that 2/3 of variance in partners' commitment to relationships could be explained by satisfaction, alternatives, and investment.
Moreover, the study found that commitment was the primary predictive measure that could determine long-term relationship success.
All of the couples were asked to fill out a questionnaire, with questions about commitment, satisfaction, quality of alternatives, and investments.
After answering all of the questions, the results were put together, and it was found that satisfaction and quality of alternatives are much more important for determining total commitment levels than investment size.
This disagrees partially with Rusbult's initial model, and supports an interdependence theory way of predicting relationship outcomes, by disregarding the investments.