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In traditional vows, married couples often make the promise to care for one another “in sickness and in health”. This vow expresses that romantic partners should remain committed to each other regardless of the obstacles that life puts in their way, including when one member of the relationship has compromised health. However, this vow seems to suggest that ill health is a condition that develops and occurs outside the context of a romantic relationship, which a couple must then manage as a unit. In the current chapter, we will highlight how this could not be further from the truth. In fact, an individual’s mental and physical health can depend on the quality of these social relationships. But how exactly do these processes occur? We will argue that the personality characteristics that each partner brings to a relationship play a role in shaping how an individual interprets and experiences their relationships, which inevitably influences one’s health. Although there are large literatures examining the associations of health with personality and interpersonal relationships independently, there are also many opportunities for these two areas of psychology to intersect in an attempt to explain the health consequences of romantic relationships as they occur across the lifespan.

In the current chapter, we describe how personality and close relationship processes may interact to influence mental and physical health. We begin with a discussion of how our romantic relationships contribute to our health and how personality can predict some of the relationship outcomes that are important in this connection. Next, we showcase some of the prominent models enabling researchers to characterize how personality and relationship factors may interact to influence health. We close with a discussion of the unanswered questions that will help to direct future research examining the combined impact that personality and relationships has on health.

2.1 How Do Our Romantic Relationships Impact Our Mental and Physical Health?

Before discussing how it is that personality and romantic relationships may interact to influence health, we must first demonstrate that: (1) our romantic relationships play an important role in determining physical and mental health, and (2) personality plays a role in determining the behaviours and experiences people have in their romantic relationships that are important to the relationship-health link. In this section, we will address the first point by describing the impact that our romantic relationships have on physical and mental health through-out the lifespan before outlining how it is that these relationships have this effect.

For decades, researchers have argued that social relationships and interactions are a basic human need that is crucial to living a happy and healthy life (e.g., Baumeister & Leary, 1995; Holt-Lunstad, Smith, & Layton, 2010). Romantic relationships are often used to vouch for this argument as those involved in a committed romantic relationship generally live longer, healthier and more satisfying lives than their noncommitted peers (Bennett, 2006; Dupre, Beck, & Meadows, 2009; Rogers, 1995). In particular, individuals in romantic relationships tend to report considerably better self-reported physical health (Lui & Umberson, 2008; Rohrer, Bernard, Zhang, Rasmussen, & Woroncow, 2008; Umberson, 1992), as well as better emotional well-being and greater life satisfaction (Bookwala & Schultz, 1996; Gove & Tudor, 1973; Horwitz, White, & Howell-White, 1996; Kessler & Essex, 1982; Tucker, Friedman, Wingard, & Schwartz, 1996; Wadworth, 2016). These effects are especially large when comparing married individuals to those who are widowed and divorced (compared to single), as the breaking of relationship bonds can have strong negative impacts on self-reported physical and mental health (Rook & Zettel, 2005; Williams & Umberson, 2004). Older adulthood is a period of the lifespan in which this association is especially critical as widowhood is typical in this age-group and older adults generally tend to already have poorer health when compared to younger adults. However, perhaps one of the most significant health benefits associated with being in a committed relationship is the minimized probability of developing a variety of acute and chronic physical and psychological conditions (Datta, Neville, Kawachi, Datta, & Earle, 2009; Nilsson, Engstrom, & Hedblad, 2008; Umberson, Williams, Powers, Liu, & Needham, 2006). This includes a substantially lower morbidity and mortality risk for cardiovascular disease and cancer, which represent two of the leading causes of death in North America (Centers for Disease Control and Prevention, 2017; Canada, 2015), as well as lower risk of anxiety and mood disorder diagnosis (see Umberson & Williams, 1999; Waite & Gallagher, 2000, for reviews), which are among the most common mental health disorders. In sum, there is a substantial body of research indicating that being involved in a romantic relationship can be beneficial for both physical and mental health. But how is it that romantic relationships have these effects on our health?

Of course, it is not merely an individual’s relationship status that impacts health, instead it is the experiences within and the quality of these relationships that influence health status (Gottman & Notarius, 2002). Indeed, many theoretical models linking relationships and health propose that the behaviours and outcomes experienced within a relationship are essential components in predicting health outcomes (Kiecolt-Glaser & Newton, 2001; Pietromonaco, Uchino, & Dunkel Schetter, 2013). This notion is supported by research indicating that having a happier and more satisfying relationship tends to coincide with living a happier and healthier life in all age groups. Specifically, those in satisfying relationships tend to report having better physical health and fewer health ailments (Bookwala, 2005; Miller, Dopp, Myers, Stevens, & Fahey, 1999; Robles, Slatcher, Trombello, & McGinn, 2014; Wickrama, Lorenz, Conger, & Elder, 1997), as well as greater psychological well-being and fewer depressive symptoms than those who are relatively unsatisfied in their relationships (Proulx, Helms, & Buehler, 2007; Whisman, 2001). Beyond relationship satisfaction, positive relationship experiences (e.g., social support, intimacy, physical touch) also have beneficial effects on physical and mental health. These positive experiences are said to alleviate the effect of stress on various psychosocial and physiological pathways that influence health (e.g., Slatcher & Selcuk, 2017). For instance, romantic partners experience lower cortisol levels on days when they engage in more physical touch (i.e., holding hands, hugging) with their spouses (Ditzen, Hoppmann, & Klumb, 2008). However, not all relationships are classified as being satisfying or characterized by positive relationships experiences. So the question becomes, when an individual is involved in an unsatisfying relationship, what happens to their physical and mental health?

As you may have expected, just as a happy and well-adjusted relationship is beneficial to health, an unhappy or poorly functioning romantic relationship can be harmful to health (Robles & Kiecolt-Glaser, 2003). In fact, individuals who are not satisfied in their romantic relationships are more likely to report experiencing a variety of physical and mental health conditions including cardiovascular disease, anxiety disorders, and depression (Frech & Williams, 2007; Hawkins & Booth, 2005; Overbeek et al., 2006). Further, negative relationship experiences (e.g., anger, relationship conflict, hostility, criticism) have also been shown to undermine health (Bookwala, 2005; Choi & Marks, 2008). This may occur because problematic social interactions can evoke negative psychological and physiological responses, which if chronically activated are associated with future health difficulties. For instance, negative relationship experiences, such as conflict and relationship strain, are associated with physiological markers of stress and detriments in immune system functioning that undermine later physical health (Kiecolt-Glaser, 2018; Kiecolt-Glaser et al., 2005; Miller et al., 1999; Robles & Kiecolt-Glaser, 2003). Similarly, these negative relationship interactions are associated with psychological distress and depression, which can have adverse impacts on long-term mental health (Fincham & Beach, 1999; Proulx et al., 2007).

The breadth of research reviewed above communicates the substantial impact that our romantic relationships have on our physical and mental health. In particular, we have outlined how relationship quality and the experiences that one has within a romantic relationship influences whether the relationship will be a benefit or a detriment to one’s health. But what are the factors that determine whether an individual will have a satisfying and functional romantic relationship? To answer this question, we will now examine the ways in which personality affects relationships and relationship quality.

2.2 Can Personality Determine Who Flourishes or Flounders Within a Relationship?

The previous section demonstrated that the behaviours and experiences that one has within a romantic relationship have a substantial impact on one’s health. However, that was only one piece of the puzzle as we also specified that we had to demonstrate that personality can determine the behaviours and experiences that an individual will likely have in their romantic relationships. In this section, we will discuss how two theories of personality can be used to influence the relationship behaviours and outcomes that we just demonstrated have considerable impact on physical and mental health.

Often our personalities play a role in how we interpret and behave within interpersonal situations. Thus, not surprisingly, personality traits are suggested to predict relationship quality, relationship experiences, relationship dissolution, and marital divorce (Roberts, Kuncel, Shiner, Caspi, & Goldberg, 2007; Robins, Caspi, & Moffitt, 2002). In fact, it is estimated that up to 60% of the variance in marital quality and 25% of the variance in divorce risk can be explained by the personality traits of the spouses involved in the relationship (Jocklin, McGue, & Lykken, 1996; Russell & Wells, 1994; Solomon & Jackson, 2014). The research linking personality to relationship experiences has primarily focused on the impact that constructs from attachment theory and the Big Five model have on relationship behaviours and outcomes. Although we acknowledge the large literature investigating other individual differences in relationship research (e.g., self-esteem, narcissism; Murray, Rose, Bellavia, Holmes, & Kusche, 2002; Brunell & Campbell, 2011), we will concentrate on discussing the influence that attachment and the Big Five personality traits have on the relationship experiences that we previously established were associated with health. However, before we begin, it should be noted that since these individual difference factors are believed to be relatively stable over time, the impacts that attachment and the Big Five traits have on relationship processes tends to be fairly stable across relationships and the lifespan.

2.2.1 Adult Attachment

Attachment theory is one of the only prominent theories of personality that was designed with interpersonal interactions specially in mind. The original purpose of attachment theory was to describe and explain the close, emotional bond that develops between an infant and his or her primary caregiver (Bowlby, 1969). However, it was quickly expanded to describe adulthood relationships as the attachment processes responsible for the bonds that develop between adults were deemed to be similar to the ones responsible for the bond that develops between an infant and caregiver (Bowlby, 1969; Fraley & Shaver, 2000; Hazan & Shaver, 1994). Regardless as to whether we are referring to children or adults, the underlying notion behind attachment theory is the same: individuals develop an attachment orientation—patterns of interpersonal cognitions, emotions, and behaviors—based on their unique interactions and experiences with attachment figures. It is these attachment orientations that guide how an individual interprets and behaves within their close relationships (Fraley & Shaver, 2000; Shaver & Mikulincer, 2007). In adulthood, people are thought to vary on two independent dimensions of attachment, which determine their attachment orientation: (a) attachment anxiety, which refers to the tendency to ruminate and be obsessively worried about close relationships due to fears of rejection and abandonment, and (b) attachment avoidance, which involves the tendency to experience discomfort in situations of physical and emotional closeness or dependence (Brennan, Clark, & Shaver, 1998; Campbell & Marshall, 2011; Fraley & Shaver, 2000). Individuals who report high levels of either attachment anxiety or avoidance are said to display an insecure attachment orientation, whereas those who report low levels on both dimensions are thought to exhibit attachment security, which refers to the tendency to feel comfortable with interpersonal closeness as well as independence. Now that the basis of attachment theory has been established, we can discuss how each attachment orientation can shape the relationship experiences that are significant to the connection between relationships and health. In particular, we will focus on relationship quality (i.e., relationship satisfaction and commitment) and stability.

When evaluating the impact that attachment has on relationships, researchers often focus on whether or not people are happy with and committed to their partner (i.e., relationship quality; Etcheverry, Le, Wu, & Wei, 2013). This focus has consistently demonstrated that individuals higher on attachment insecurity experience lower levels of relationship satisfaction in romantic relationships compared to those with greater attachment security (see Mikulincer & Shaver, 2016 for detailed review). In fact, these individuals report lower daily relationship satisfaction (Campbell, Simpson, Boldry, & Kashy, 2005; Lavy, Mikulincer, & Shaver, 2013; Neff & Karney, 2009), and tend to be less satisfied with their relationships in the first 3 years of marriage (Davila, Karney, & Bradbury, 1999). The negative impact that attachment insecurity has on romantic relationships is not limited to relationship satisfaction as similar patterns have been seen for relational commitment. Specifically, those who exhibit attachment insecurity often report being less committed to their romantic partner (see Mikulincer & Shaver, 2016 for detailed review). Given that relationship quality is one of the largest predictors of relationship stability, individuals with attachment insecurity also tend to be in relationships that are characterized by instability. In fact, anxious and avoidant individuals tend to have shorter dating relationships and marriages when compared to more secure individuals (Birnbaum, Orr, Mikulincer, & Florian, 1997; Crowell & Treboux, 2001; Duemmler & Kobak, 2001; Kirkpatrick & Davis, 1994). However, the reason for this instability differs according to the individual’s attachment orientation. In particular, despite being relatively unsatisfied and uncommitted to their relationships, anxious individuals are overly dependent on the affections of their partner, while also having a generalized fear of abandonment. Thus, these individuals are at greater risk of remaining in unhappy marriages for extended periods of time (Davila & Bradbury, 2001; Kirkpatrick & Davis, 1994). But these relationships are often unstable as anxious individuals commonly breakup and re-partner with the same people multiple times. On the other hand, since avoidant individuals have an overall dislike of emotional intimacy, these individuals have a higher likelihood of terminating a relationship as soon as relationship distress is experienced (Kirkpatrick & Davis, 1994).

The impact that attachment insecurity has on relationship quality and stability may be understood by the behavioural tendencies associated with each of the insecure attachment orientations. For instance, due to their fears of rejection and abandonment, anxious individuals require constant affection and reassurance from their partner in order to feel a sense of emotional closeness and stability (Hazan & Shaver, 1994; Shaver & Mikulincer, 2007). This results in these individuals consistently engaging in behavioral and emotional strategies that involve seeking proximity and closeness to a romantic partner (i.e., hyperactivating strategies; Mikulincer & Shaver, 2012). However, they are often disappointed by their partners’ lack of reciprocity of affection, which has been suggested to lead to low levels of satisfaction and commitment among anxious individuals. In comparison, because avoidant individuals are uncomfortable with closeness or dependence, these individuals often attempt to maintain a sense of autonomy while in a romantic relationship (Hazan & Shaver, 1994; Shaver & Mikulincer, 2007). Thus, avoidant individuals engage in behavioral and emotional strategies that distance themselves from a romantic partner (i.e., deactivating strategies). These include being more critical of their partner, tending not turn to their partner for support, and ignoring the emotional cues and signals in their relationship (Campbell et al., 2005; Simpson, Rholes, & Nelligan, 1992). It is these dismissive tendencies that are believed to account for the consistently low levels of relationship satisfaction and commitment reported by individuals high in avoidance.

Although attachment theory takes a relationship perspective on individual differences and applies it to social relationships, some researchers still prefer to take a broader personality approach when examining the impact that personality has on our relationships. Thus, many researchers have examined the impact that the Big Five traits have on relationship experiences and outcomes. Despite having some empirical overlap with attachment orientations (e.g., Noftle & Shaver, 2006), an entirely separate literature examining the associations between the personality traits outlined in the Big Five model and relationship functioning has emerged.

2.2.2 The Big Five Model

The Big Five model is perhaps the most popular and well-known theory of personality. The five personality traits that make up this model—agreeableness, conscientiousness, neuroticism, extraversion, and openness—have emerged as an empirically based framework that captures the major individual differences that exist between people (John & Srivastava, 1999). Although not developed with interpersonal relationships specifically in mind, the personality traits outlined in the Big Five nevertheless impact how we understand, experience and act within our social relationships. Below, we will describe each of the Big Five personality traits and outline how these traits can shape relationship quality and stability, which we have been shown to be related to health.

Agreeableness is a social trait that reflects individual differences in the propensity to be altruistic, trusting, modest, and warm (John & Srivastava, 1999). Agreeable individuals are more motivated to maintain positive relationships with others and they tend to engage more in social behaviors that facilitate intimacy (Jensen-Campbell & Graziano, 2001). Not surprisingly, agreeableness has been consistently related to many positive relationship variables. For instance, agreeableness is positively associated with marital and relationship satisfaction, and negatively associated with both marital dissatisfaction and divorce (Dyrenforth, Kashy, Donnellan, & Lucas, 2010). In addition, agreeable individuals experience greater intimacy, commitment, and passion within their relationships (Ahmetoglu, Swami, & Chamorro-Premuzic, 2010). Although agreeableness is linked to relationship quality, little research has directly examined why the two are linked. Some researchers have suggested that the link may be explained by the impact that agreeableness has on conflict. Generally speaking, agreeable individuals tend to report having fewer negative interactions with their romantic partners (Donnellan, Conger, & Bryant, 2004), and use more productive conflict resolution skills when negative interactions present themselves in a relationship (Graziano, Jensen-Campbell, & Hair, 1996).

Conscientiousness is a trait of self-discipline that reflects individual differences in the propensity to plan, organize, delay gratification, and be achievement-oriented (Roberts, Jackson, Fayard, Edmonds, & Meints, 2009a). Conscientiousness has been found to be positively related to relationship satisfaction in both dating and married couples (Dyrenforth et al., 2010; Engel, Olson, & Patrick, 2002). Further, it is positively associated with many other positive relationship experiences such as commitment, passion, and intimacy (Ahmetoglu et al., 2010; Engel et al., 2002). It is thought that the achievement orientation of those with a conscientious personality motivate these individuals to make their relationships work; while their other tendencies allow them to consistently enact positive relationship behaviors, such as remembering relevant information, being reliable, and upholding promises (Jackson et al., 2010). Further, the self-control habits of conscientious individuals are believed to prevent relationship problems as these individuals can easily avoid temptations, such as enacting revenge and committing infidelity (Engel et al., 2002). The responsible, dependable, and hardworking nature of those with a conscientious personality generally creates fewer areas of disagreement (Donnellan et al., 2004). However, future work is needed to explicitly test the mechanisms that link conscientiousness to these positive relationship experiences and outcomes.

Neuroticism reflects individual differences in the tendency to experience negative emotions and emotional instability (John & Srivastava, 1999). Early personality researchers identified that many of these tendencies and emotional experiences create and define unhappy and unstable relationships (Karney & Bradbury, 1995). A significant body of research has supported this insight by linking neuroticism with poor relationship quality (e.g., Barelds, 2005; Davila, Karney, Hall, & Bradbury, 2003; Donnellan et al., 2004), and a greater risk of marital dissolution (Kurdek, 1993; Roberts et al., 2007). In fact, neuroticism has been found to have the strongest association with marital satisfaction when compared to the other four Big Five personality traits (Heller, Watson, & Ilies, 2004). This is also found when examining the effects of partner personality—having a highly neurotic partner is among the largest predictors of life and relationship satisfaction (Chopik & Lucas, 2019). These results may be explained by the tendencies of neurotic individuals to express more criticism, contempt, and defensiveness, which may damage a relationship. Further, these individuals use greater avoidance coping (Lee-Baggley, Preece, & DeLongis, 2005) and report experiencing fewer positive and more negative social interactions overall (Russell & Wells, 1994). Such characteristics may lead to conflicts in a romantic relationship and prevent others from engaging in socially supportive behaviors. Overall, when comparing the Big Five personality traits, neuroticism is generally the strongest and most consistent trait impacting our social relationships. However, unlike agreeableness and conscientiousness, neuroticism is characterized by lower relationship quality and more negative relationship experiences.

Like agreeableness, extraversion has a strong sociability component and refers to individual differences in the tendencies to be sociable, active, assertive, and to experience positive affect (John & Srivastava, 1999). It is often believed that extraverted individuals should have more positive relationship experiences because these individuals are better equipped to communicate their desires, wants, and intentions than those low on extraversion (Taraban, Hendrick, & Hendrick, 1998). However, the available literature on the associations between extraversion and relationship outcomes has yielded inconsistent findings (e.g., Donnellan et al., 2004; Watson, Hubbard, & Wiese, 2000). For instance, extraversion has been associated with several positive relationship variables, such as satisfaction (Solomon & Jackson, 2014) and passion (Ahmetoglu et al., 2010). But it has also been associated with many negative relationship variables, such as lower relationship satisfaction (for men; Bentler & Newcomb, 1978) and marital instability (Ahmetoglu et al., 2010). The inconsistent findings regarding extraversion may be explained by the fact that extraversion appears to capture individual differences that relate to social impact (as opposed to maintaining positive relations), which may not be an important process in shaping romantic relationships (Tobin, Graziano, Vanman, & Tassinary, 2000). Regardless, given the empirical inconsistencies concerning the role of extraversion in close relationships, future work will be needed to create a clearer picture.

Openness reflects individual differences in the propensity to be imaginative, creative, curious, and adventurous (John & Srivastava, 1999). Originally, it was thought that openness may facilitate relationship quality and maintenance by promoting intellectual approaches to problem solving, more flexible attitudes towards change, and a willingness to try new things within a relationship (Robins et al., 2002). However, it appears that openness is often unassociated or has conflicting associations with relationship quality (e.g., Chopik & Lucas, 2019). Meta-analyses examining the impact of personality on relationship quality has demonstrated that there is often no relation between openness and relationship satisfaction (Malouff, Thorsteinsson, Schutte, Bhullar, & Rooke, 2010). Further, openness has not been found to have a significant association with other relationship factors, including intimacy, passion or commitment (Engel et al., 2002). Thus, openness may not be the most important individual difference characteristics to consider when attempting to understand relationship processes.

The research reviewed above implies that individual differences in attachment and the Big Five traits help to explain variability in how individuals interpret, behave, and experience their romantic relationships. We will now combine this discussion with that outlining the ways in which relationship processes influence health so that we may consider how it is that personality and relationship experiences may interact to influence physical and mental health.

2.3 How Do Individual Differences in Personality Interact with Relationship Processes to Influence Health?

The first section of the current chapter focused on establishing the role that various relationship processes have on physical and mental health. We followed this with a discussion of how personality plays a role in determining the relationship processes that are important to the relationship-health link. However, the independent discussion of these two topics defeats the overall purpose of the current chapter to consider how it is that personality and relationship science may work together to impact health across the lifespan. Thus, in this section, we will work towards outlining how it is that the research reviewed in the two previous sections may be combined to provide us with a better understanding of how our relationships and personality traits impact our mental and physical health.

The notion of combining relationship and personality science in an effort to better understand health is not a completely novel idea. For instance, Pietromonaco et al. (2013) developed a model outlining how individual differences in attachment interact with relationship processes to influence physical health. The model suggests that differences in attachment help determine how an individual behaves in a relationship, which subsequently impacts how that relationship functions. These relationship behaviours and outcomes shape physiological stress response patterns, affect, and health behavior engagement, which contribute to later physical health and disease outcomes. Similarly, Slatcher and Selcuk (2017) designed a broader model to explain how personality and marital experiences interact to impact physical health. Within this model, individual difference characteristics (not limited to attachment) influence the positive (i.e., strengths) and negative (i.e., strain) aspects of a relationship. These aspects are thought to impact physical health by influencing various psychological (i.e., affect and cognitions) and behavioural (i.e., health behaviours) mechanisms. Although separate models, these two frameworks tell the same story: personality plays a role in determining various relationships processes, which subsequently influence health and disease outcomes.

Unfortunately, there is very limited evidence to support theoretical frameworks like those designed by Pietromonaco et al. (2013), and Slatcher and Selcuk (2017). In fact, the state of the current literature follows the same structure as the current chapter: there are the researchers who focus on the associations between relationships and health, and then there are a variety of other researchers linking personality to relationship processes and health. And, it appears as though many of the personality and relationship researchers working in the area of health psychology ignore the existence of one another. The emphasis that is placed on examining either the influence that personality or relationship processes have on health creates an incomplete understanding of various important health outcomes. In other words, although comprehensive models have been developed, we are still unsure as to how personality characteristics and relationship processes may be working together to influence health. Despite the lack of research combining these two areas of psychology, there are two ways in which personality and relationship processes may be combined to influence health. The first is that individual difference characteristics moderate the link between relationship processes and health (as seen in Slatcher & Selcuk, 2017). That is to say that the extent to which our relationships impact our health is dependent on our personality. This pathway has found some support as relationship conflict has been shown to be related to disruptions in immune systems responses, particularly among highly anxious individuals (Powers, Pietromonaco, Gunlicks, & Sayer, 2006). Broadly, this research suggests that the impact that negative relationship interactions have on health is more prominent for individuals with certain personality traits, in this case individuals who are anxiously attached. But overall, there is a lack of studies examining the possible moderators for the links between relationships and health (Robles et al., 2014).

The second way in which personality and relationship processes may be combined to influence health is that relationship experiences may mediate the link between personality and health (as seen in Pietromonaco et al., 2013). This pathway takes a slightly different approach as it suggests relationship processes are able to explain the association between personality and health. In other words, mediation implies that personality does not have a direct effect on health. Instead personality influences health via the relationship processes that personality impacts. As we have demonstrated in the two previous sections of this chapter, there is piecemeal support for the mediation argument. That is, personality plays a role in determine various relationship processes, which later have an impact on physical and mental health. However, this is insufficient support and there are few studies that have examined both personality and relationships experiences together in an effort to establish whether relationship processes can explain the association between individual difference characteristics and health.

In sum, a handful of researchers have clearly outlined how it is that relationship processes and personality may interact to influence physical and mental health. We reviewed two models which each take a different approach in combining relationship and personality science to explain health. Although theoretically sound, these models are lacking in empirical support. But in order to test these models correctly, researchers need to ensure that the data and the analytics strategy are sufficient for such an undertaking. Thus, we will now discuss the ways in which we think researchers should be testing these models and answering the questions posed in the current chapter.

2.4 Future Directions

When conducting research including romantic partners it is important to remember that relationships are dynamic and reciprocal. That is, the reactions, experiences, and traits of one partner influence and are influenced by those of the other partner. This mutual influence between romantic partners becomes apparent when examining models such as the one designed by Pietromonaco et al. (2013) as the impact that each partner has on one another is clearly delineated within their framework. Thus, in order to formally test the mechanisms through which individual differences and close relationships influence health, researchers need to design studies in a way that allows for an assessment of both partners’ characteristics and outcomes (i.e., dyadic research). In particular, the data analytics that are needed for dyadic studies require an adjustment for non-independence as partners’ responses are often impacted by one another. Further, the study methods and analyses need to account for how each person’s own characteristics, those of their partner, and the interaction between their own and their partner’s characteristics predict the various outcomes of interest (see Kenny, Kashy, & Cook, 2006). The Actor–Partner Interdependence Model (APIM; see Kenny et al., 2006; Kenny, 2018) is a popular analytic model that enables researchers to test the each of these pathways. In particular, APIM allows researchers to examine the extent to which: (a) the characteristics of each relationship partner influence their own outcomes (i.e., actor effects), (b) the characteristics of one relationship partner influence the other partner’s outcomes (i.e., partner effects), and (c) the characteristics of one relationship partner interact with those of the other partner to predict one or both partners’ outcomes (i.e., interactive actor x partner effects). To date, many dyadic studies that include individual difference measures have tried to merely establish links between the characteristics of each spouse to each spouse’s health status (Kim, Chopik, & Smith, 2014; Roberts, Smith, Jackson, & Edmonds, 2009b). These studies ignore the possible relationship processes that may act as mechanisms for the associations between personality and health, such as those outlined in the theoretical frameworks designed by Pietromonaco et al. (2013) and Slatcher and Selcuk (2017). Thus, much more dyadic research is needed to establish how it is that personality characteristics and relationships experiences of each partner may work together to impact the health status of each of the partners in a romantic relationship. Beyond conducting dyadic research, it is necessary for health research to be conducted longitudinally as many health outcomes develop over time after many social interactions with a romantic partner. Naturally, this adds to the complexity of the models discussed above, as now the dyadic analytics also need to model how personality and relationship processes unfold over time to influence the health conditions that develop across the lifespan (Ledermann & Kenny, 2017).

In sum, it is important for future research to ensure that: (a) dyadic longitudinal data is collected on personality, relationship processes, and health outcomes, and (b) the analytic strategy used allows for researchers to correctly address all the different factors that play a role in deciding how the relationship processes and personality of each partner may work together to influence physical and mental health.

2.5 Conclusion

At the beginning of this chapter, we argued that the personality characteristics each partner brings to a relationship play a role in shaping how an individual interprets and experiences their relationships, which inevitably influences one’s health. We believe that the current chapter has outlined a solid theoretical basis for this argument. However, the current piecemeal empirical evidence that exists to support this argument is not sufficient to glean strong conclusions regarding the value of the discussed theories. Thus, it is our hope that this chapter provides future researchers with the necessary theoretical and practical knowledge to test this argument more thoroughly as we believe that integrating the science of individual differences with relationship science can bring us closer to the prospect of living happily—and healthily—ever after.