The Investment Model was put forward by Rusbult et al. (2001), as a development of Social Exchange Theory. The rationale for developing SET further was that many couples stay together despite the costs outweighing the rewards, so there must be some other factors that keep them together. Rusbult's Investment Model investigates what these other factors might be.
According to Rusbult's proposal, there are three major factors that maintain commitment in relationships: satisfaction level, comparison with alternatives and investment size.
Satisfaction level and comparison with alternatives are based on the idea of comparison levels from Social Exchange Theory. People will have a high level of satisfaction with relationships if they have more rewards (companionship, attention, emotional support) and fewer costs (arguments, time). They also tend to be committed to relationships if, when asking themselves, 'Is there a better alternative to satisfy my needs?' the answer is ‘no’. Alternatives can include staying on their own and not engaging in romantic relationships at all, as well as finding a new partner.
However, for Rusbult et al., the most important factor that maintains commitment to a relationship is investment. Investment refers to the number of resources, both tangible, like money or possessions, and intangible, like happy memories, that people will lose if they leave relationships. The model proposes two types of investment: intrinsic and extrinsic. Intrinsic investment comprises the things we put directly into the relationship, such as effort, money, possessions, self-disclosure. Extrinsic investment refers to the things that are brought to people's life through the relationships, such as children, friends and shared memories.
Because both intrinsic and extrinsic investments can potentially be lost if relationships end, Rusbult et al. concluded that the bigger the investment, the more likely people are to stay in relationships. Therefore, it is the investment size that influences commitment to relationships, rather than just the level of satisfaction or existence of potential alternatives.
In addition to the factors influencing partners’ commitment, Rusbult et al. also identified maintenance mechanisms partners use to keep relationships going.
These mechanisms are:
Research Examining the Investment Model
There are numerous research studies supporting the Investment Model. Impett, Beals and Peplau (2002) conducted a longitudinal study using a large sample of married couples over an 18 months period. They found that stability of the relationships positively correlated with commitment shown by the partners.
Rhahgan and Axsom (2006) studied a group of women and found that all three factors identified by Rusbult et al. (satisfaction, comparison with alternatives and investment) featured in participants' decision to stay with their partner.
Similar trends were found in Le and Agnew’s (2003) study. They conducted a meta-analysis of 52 studies, featuring 11,000 participants in total, and discovered that satisfaction, comparison with alternatives and investment greatly contributed to commitment; and that commitment was a defining feature of long-lasting relationships.
Evaluation of the Investment Model
One strength of the Investment Model is that it is supported by numerous research studies. For example, Le and Agnew (2003) found that satisfaction, comparison with alternatives and investment greatly contributed to commitment. This supports the model’s claims about the factors contributing to commitment and about commitment being the most promising feature in successful long-term relationships, and thereby increases the reliability of the model.
The Investment Model provides a plausible explanation for why people stay in abusive relationships. According to the 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 into abusive relationships supports this idea. For example, Rusbult and Maltz, in their study of 'battered' women, found that women were more likely to return to an abusive partner if they felt they had invested in the relationship and they didn't have any appealing alternatives. This shows that the Investment Model can be applied to a wide range or relationships experiences that the SET and Equity Theory fail to explain, thus increasing the Investment Model’s application to everyday relationships.
The majority of research into the Investment Model is correlational, so psychologists are unable to conclude that investment causes commitment in relationships. This limits the predictive validity of the model, as it would fail to predict which types of investment and how much investment will lead to long-term commitment to a relationship. Lack of predictive validity also makes the Investment Model less scientifically rigorous, as the ability to predict people's behaviour, in this case, whether or not they will stay committed to the relationship, is one of the main goals of psychology as a science.
Some psychologists point out that most evidence for the Investment Model comes from interviews and questionnaires, which are known to be subjective and unreliable. However, other researchers argue that, because satisfaction, investment and commitment are subjective values and depend on people's perception, using self-report techniques is an appropriate way to test the Investment Model. Therefore, data obtained through self-report techniques may provide a more realistic picture of reasons for relationship satisfaction and how it is related to investment and commitment, therefore making Investment Model more valid.
Even though the importance of investment was clearly demonstrated by research, some psychologists think that Rusbult’s idea of relationship investment is oversimplified. For example, 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 their view, partners will be committed to staying in the relationships because they want to see these plans realised. This shows that investment in romantic relationships is a complex phenomenon, consisting of many different factors, which makes the Investment Model reductionist.
Culture bias doesn't seem to be an issue for the Investment Model. Le and Agnew’s (2003) meta-analysis of 52 studies found support for the Investment Model across individualist and collectivist cultures, such as in the USA (individualist culture) and in Taiwan (collectivist culture). Furthermore, the Investment Model, as an explanation of relationship maintenance, is also shown to be valid for different sub-groups, such as friendships; homosexual relationships; and cohabiting couples, etc. This suggests the universality of the Investment Model, making it applicable to wide range of relationships.
The fact that the evidence for the Investment Model is found across cultures may suggest that the human need for investment and commitment to relationships developed through the process of natural selection to help people survive and reproduce. For example, parents who are committed to their relationship and invest in it will have a higher chance of ensuring their children's survival and therefore of passing on their genes. This means that the Investment Model supports the nature side of the nature-nurture debate.
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