Some psychologists suggest there is problems measuring the key variables involved due to the reliance on self-report techniques, such as questionnaires and interviews.
The majority of research into the Investment Model is correlational, so psychologists are unable to conclude that investment causes commitment in relationships.
Le & Agnew (2003) Meta analysis of 52 studies including 11,000 participants from 5 countries. They found that satisfaction, comparison with alternatives and investment size all predicted relationship commitment. Relationship where commitment was greatest where most stable and long lasting. Goodfriend and Agnew (2008) argue that it is not just things we bring to the relationships that could count as investment, but also a couple's plans for their future. In the early stages, partners will have made very few actual investments.
According to the investment model, if a partner feels that the investment they made into relationships will be lost if they leave, they are more likely to stay in a relationship even when the costs are high (such as physical or emotional abuse) and rewards are few. Research like Rusbult and Martz supports this.
Rusbult’s investment model of commitment has got wide application in society e.g. across countries and sexual orientations
Le and Agnew’s (2003) meta-analysis reviewed the results of 52 different studies that used participants from five different countries (US, UK, Netherlands, Israel and Taiwan). They also included both hetrosexual and homosexual couples; couples that were married and unmarried; romantic relationships, abusive relationships and friendships.