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Psychosocial adaptation and quality of life in multiple sclerosis: assessment of the disability centrality model.

This article describes an evaluation of the disability centrality model among a sample of persons with multiple sclerosis (MS). The twofold purpose of this research was first to enhance current understanding of the relationship between MS, quality of life (QOL), and psychosocial adaptation, and second, to further assess the validity of this recently proposed model. The disability centrality model (Bishop, 2005a & b) is a multidimensional, quality of life-based model of the mechanisms of impact and adaptive response to chronic illness and acquired disability.

Multiple sclerosis (MS) is one of the most common acquired neurological diseases (McNulty, Livneh, & Wilson, 2004), affecting approximately 400,000 people in the United States, or about 1 out of every 750 persons (National Multiple Sclerosis Society [NMSS], 2006), and more than one million people worldwide (Munschauer & Weinstock-Guttman, 2005). Typically diagnosed among people between the ages of 20 and 40 years, MS is the leading cause of neurological disability in early to middle adulthood. Multiple sclerosis is currently thought to be an autoimmune disease that affects the central nervous system. Research related to a comprehensive understanding of the complex neurological processes and systems involved in the MS disease process is rapidly evolving, and although there currently is no cure for MS, a variety of medications and treatments have been identified that can slow its course or alleviate symptoms (NMSS, 2006).

Typically presenting with a relapsing-remitting course, after an average of 15 years, most people with MS experience a secondary progressive phase wherein the course becomes either continuously progressive or progresses between exacerbations (Johnson et al., 2006). The various neurochemical processes by which MS affects the central nervous system can result in a broad array of symptoms. The most commonly reported of these include changes in mood and cognitive function, bowel and bladder dysfunction, fatigue, pain, balance problems, difficulties with walking, vision problems, and sexual dysfunction (NMSS, 2006). Because onset is associated with a period of life in which individuals are establishing families, careers, and financial security (King, 2001), MS and its attendant symptoms can create a significant disruption in psychosocial functioning. The illness-related symptoms, medical treatments and their adverse effects, and unpredictable course and prognosis of MS have been associated with a significant impact on quality of life (QOL) and psychosocial adaptation.

Multiple Sclerosis, Quality of Life, and Psychosocial Adaptation

People with MS have frequently been found to report lower QOL than persons without a disability and, in some studies, lower than persons with other chronic illnesses, including rheumatoid arthritis, epilepsy, and diabetes (Benito-Leon, Morales, Rivera-Navarro, & Mitchell, 2003; Pfennings et al., 1999). Understanding the complex and potentially unique mechanisms by which MS affects QOL and psychosocial well-being is a relatively recent endeavor (Benito-Leon et al., 2003), but one that has received increased attention as QOL has gained prominence as an important measure of treatment efficacy and rehabilitation outcome (Johnson, Amtmann, Yorkston, Klasner, & Kuehn, 2004; Wilson, Goetz, & Stebbins, 1996).

Recent studies aimed at delineating the impact of MS on QOL (e.g Benito-Leon et al., 2003; Ford, Gerry, Johnson, & Tennant, 2001; Johnson et al., 2004; Koch, Rumrill, & Roessler, 2001; McReynolds, Koch, & Rumrill, 1999; Miller & Dishon, 2005; Pfennings et al., 1999; Schwartz & Frohner, 2005; Thompson, 1999) have confirmed that this impact results from both the cognitive and physical symptoms of MS, and psychosocial factors. These factors include anxiety associated with the unpredictable course of MS, disruptions or limitations in role functioning, and strain on family relationships and other social support structures (Koch et al; McReynolds et al., Miller & Dishon; Thompson).

It has also been noted in this research that many persons with MS who are experiencing significant health problems and functional limitations nevertheless report high levels of well-being, or subjective QOL (SQOL) (Johnson et al., 2004) and psychosocial adaptation (Antonak & Livneh, 1995; Warren, Warren, & Cockerill, 1991; Wineman, 1990). This apparently "paradoxical" situation (Albrecht & Devlieger, 1999; Johnson et al., 2004) that has also been observed among persons with other chronic illnesses, suggests that although they are the most frequently explored aspects of the MS-QOL relationship, disease symptoms and health status are neither solely responsible for, nor predictably related to SQOL (Ford et al., 2001), or psychosocial adaptation. Rather, researchers working from a variety of perspectives have proposed that the situation involves complex interrelationships between the variables, and various adaptive processes (Johnson et al.).

Although identifying the MS-related variables that are associated with reduced QOL and increased psychosocial distress is important, it is equally important from a clinical perspective to understand both: (a) the mechanisms by which these variables produce these effects, and (b) the processes that people employ to adapt to this impact. Such understanding is necessary to develop both preventative and responsive rehabilitation interventions.

In one of the most extensively researched models of psychosocial adaptation among persons with MS, the illness intrusiveness model, Devins (1994; Devins et al., 1983) proposed that disease and treatment factors associated with chronic illness compromise psychosocial well-being indirectly by: (a) reducing positively reinforcing outcomes of participating in meaningful and valued activities, and (b) reducing feelings of personal control, by limiting the ability to obtain positive outcomes or avoid negative ones. In essence, Devins, and others working with this theory (e.g., Mullins et al., 2001), have identified two underlying and dynamically-related factors that appear critically involved in the MS-QOL relationship: satisfaction and control. Incorporating recent QOL research and perspectives from the fields of clinical and social psychology (e.g., Dembo, Leviton, & Wright, 1956; Schwartz & Sprangers, 2000; Wright, 1983), the disability centrality model incorporates and extends Devins' theory with respect to these factors.

The following discussion provides a brief overview of the disability centrality model. Readers seeking a more in-depth discussion of the model's background and rationale are referred to Bishop (2005a & b). Following this overview, the methods and results of the present study are provided and the clinical implications for rehabilitation professionals explored.

Disability Centrality Model of Psychosocial Adaptation

Although there is no universally accepted definition of psychosocial adaptation, most definitions of this construct share two basic ideas: (a) that it involves a continuous, complex response to an experience that affects multiple dimensions (e.g., social, emotional, physical) of a persons life, and (b) that both the experience and the response are highly subjective and individual in nature (Bishop, 2005b). Given these characteristics, an appropriate framework for assessing psychosocial adaptation must necessarily be both sufficiently broad to capture the impact of chronic illness or acquired disability (CIAD) across domains, and sensitive to the individual's subjective experience of this impact. The first tenet of the present model is that when defined as a subjective and multidimensional construct, QOL represents such a framework.

Quality of life is defined here as the sense of overall well-being resulting from an individual's cumulative evaluation of satisfaction within personally or clinically important domains. This conception of QOL has been alternately referred to as subjective QOL (Cummins, McCabe, Gullone, & Romeo, 1994; Frisch, 1999; Michalos, 1991) and subjective well-being (Ormel, Lindenberg, Steverink, & Verbrugge, 1999). Over the last three decades, QOL research has increasingly supported the existence of a relatively small set of life domains that people consider when evaluating their SQOL (e.g., Bowling, 1995; Cummins, 1997; Frisch, 1999). Among the most frequently and consistently identified domains are physical health, psychological or emotional health, social support, employment or productivity, and economic or material well-being.

Quality of life researchers have also proposed that these individual domains are valued differently by different people (e.g., Campbell, Converse, & Rogers, 1976; Diener & Diener, 1995; Frisch, 1999; Michalos, 1991), or by the same person over time or over the course of an illness (Hickey et al., 1996). The term "centrality" is used here to represent this concept. The term "psychological centrality" was introduced by Rosenberg (1979) in the context of his theoretical framework of self-concept. He proposed that self-concept consists of a set of hierarchically organized components, and that for any given individual some components may be more central to the self-concept than others. In the present context, SQOL, like self-concept, is similarly said to consist of hierarchically organized domains.

The model's second tenet, derived from this concept, is that SQOL is disproportionately influenced by satisfaction within those domains that are more important (or more central) to the individual. That is, satisfaction in more important or highly valued areas of life will have more influence, or more weight, in evaluations of overall well-being than domains of lesser importance (Frisch, 1999). By extension, satisfaction in more important domains may mitigate or compensate for dissatisfaction in less important domains (Gladis, Gosch, Dishuk, & Crits-Christoph, 1999).

This premise has been supported to some extent by the work of previous researchers (e.g., Andrews & Withey, 1974; Campbell et al, 1976; Diener & Diener, 1995; Michalos, 1991), and has been incorporated in the development of several QOL measures that include a domain-importance rating (e.g. Cummins, 1997; Ferrans & Powers, 1985; Frisch, Cornell, Villanueva, & Retzlaff, 1992). It should be noted, however, that despite the intuitive appeal of the domain weighting approach, there has been some recent debate in the QOL research over its utility in practice. A number of researchers have reported that the practice of importance weighting, typically achieved by multiplying satisfaction ratings by importance ratings, may add little if any sensitivity to QOL measurement. Indeed, in some studies, the multiplicative composite of satisfaction and importance has proved practically indistinguishable from the use of satisfaction alone (Cummins et al., 1994; Russell, Hubley, Palepu, & Zumbo, 2006; Trauer & Mackinnon, 2001).

Several methodological and theoretical concerns with the domain weighting approach have also been identified, and may account for these findings. These include the relatively low reliability or internal consistency of importance scores, and their low temporal stability (Russell et al., 2006). Undoubtedly related to the problem of internal consistency is the fact that domain importance may be interpreted by the respondent in many ways, including: (1) how satisfied one is with the domain, (2) how salient the domain is currently (perhaps because it is particularly dissatisfying), (3) how important the domain is to one's self-concept or self-view, and others. A specific context for defining importance is rarely provided in instruments that include an importance scale. Despite these conflicting findings and concerns about the practical utility and appropriate method of importance weighting, research with the present model to date has supported its use (Bishop, 2005a).

The third tenet of the present model is that people seek (and actively work) to achieve and maintain a maximal level of overall SQOL in terms of an internal and personally derived set-point. Quality of life researchers have consistently found that most people rate their SQOL as being relatively high (i.e., above average or above the mid-point of measurement scales) (Cummins, 1998, 2000). This phenomenon has been found to be the case across geographic and cultural boundaries and regardless of objective circumstances (Cummins, 2000; Diener, Suh, Lucas, & Smith, 1999).

In combined reviews of large scale, international studies that measured 'life satisfaction', Cummins (1995, 2000) has consistently found the normative range to lie between 70-80% of the scale maximum among Western and non-Western populations. These findings suggest that maintaining a positive level of SQOL is both normative and adaptive, from both the phylogenetic and the individual perspective. Diener and Diener (1995) suggested that a positive SQOL baseline is adaptive from an evolutionary perspective in that it allows for greater opportunities for social and personal advancement, exploratory behavior, and reliable coping resources. Lazarus (1991) and Cummins (2000) have suggested that maintaining a high SQOL set-point provides the individual a buffer against negative emotional or behavioral experiences. These findings have also been interpreted as supporting the existence of various forms of adaptive or homeostatic mechanisms (Cummins, 1997; 2000; Cummins, Gullone, & Lau, 2002; Johnson et al., 2004), in which an adaptive response is employed when SQOL drops below the individual's set-point.

Mechanisms of Impact and Adaptive Response

The onset of chronic illness or acquired disability frequently results in an initial reduction in overall SQOL. The disability centrality model suggests that this reduction occurs to the extent that the illness (1) reduces opportunities to experience satisfaction in centrally important areas of life, (2) increases the frequency with which negative emotions are experienced, and (3) reduces feelings of personal control over changing one's experience. Because overall QOL is hypothesized to be disproportionately influenced by satisfaction in more important domains, the resulting reduction in overall QOL depends on the degree to which more important domains are affected.

Satisfaction

Based on the model of SQOL described in the preceding paragraphs, the proposed maintenance of a high level of overall SQOL depends upon the ability to maintain satisfaction over time in those domains that are most central to the individual. When satisfaction cannot be maintained, the model suggests that people will engage in specific adaptive responses. If a previously highly central and highly satisfying domain becomes less satisfying for a period of time, a reduction in SQOL will be experienced. Because the individual will seek to return to their set-point, they will respond either by engaging in efforts at controlling the change and eliminating those factors that are perceived to be reducing satisfaction, or else by rearranging the order of domain importance such that more satisfying domains become more central. Another way to consider this is that after a period of time is spent engaging in ineffective efforts at regaining a prior SQOL in previously satisfying areas of life, eventually people accept that things must change and focus their thoughts and their resources on other areas in which satisfaction is still attained or attainable.

Inherent in this framework is that the maintenance of a homeostatic level of SQOL requires a subtle and delicate balance. In the absence of significant stressors, this process likely proceeds with relatively minor corrections being made over time with little if any conscious awareness. However, in the face of more significant and complex stressors such as chronic illness the imbalance may be of such significance that more active and focused responses are required.

Considering the physical, cognitive, and emotional sequelae frequently associated with MS, a situation in which satisfaction in the various domains of life may be threatened is not difficult to envision. The psychological distress, fatigue, prolonged medical treatment and its side effects, and interference in the performance of daily activities may affect participation across the range of roles and social relationships.

Control

The existence of a relationship between perceived control and SQOL has been increasingly recognized in recent years (Pallant, 2000). The maintenance of a relatively stable and predictable psychological and physical environment provides a number of features that have been identified as important to the maintenance of SQOL. Such an environment, for example, enables the setting, striving for, and attainment of goals; the experience of positive emotions that arises from anticipating positive events; and the ability to estimate the effort and resources necessary to effectively cope with negative or threatening events (McNulty et al., 2004).

The experience of reduced control has been identified as a hallmark of MS and, along with the related concept of illness uncertainty (Mishel, 1988), has frequently been associated with such outcomes as depressed mood and hopefulness, reduced quality of life, and poor psychosocial adjustment (Devins & Shnek, 2001; McNulty et al., 2004; Wineman, Schwetz, Goodkin, & Rudick, 1996; Wineman, O'Brien, Nealon, & Kaskel, 1993). The onset of MS has frequently been associated with increased risk for negative affect (Antonak & Livneh, 1995) and more than half of people with MS will have a major depressive episode during the course of their illness (NMSS, 2006).

Although control is a broadly defined and complex construct, for the purpose of the present model control is defined in the specific context of efforts aimed at reducing or eliminating factors that reduce satisfaction. When chronic illness and its effects are defined as such factors, then control may be enhanced through self-management.

For persons with chronic illnesses such as MS, self-management has been identified as an important component in combating the experience of reduced control (Devins & Shnek, 2001). Self-management involves taking active responsibility for, and informed control of one's disability or illness. This includes becoming an active and informed partner in the relationship with health care providers and a participant in treatment decisions, adhering to treatment regimens, and gaining information about how one's behavior may affect disease or disability course.

Higher levels of self-management have been associated with increased perceptions of control over both illness and non-illness aspects of life among persons with chronic illnesses (Devins, 1994, Dilorio, Faherty, & Manteuffel, 1992). Unfortunately, self-management is relatively unexplored in the MS literature. Because of the significant clinical implications of a relationship between self-management and an overall sense of increased control, this relationship was specifically evaluated in the present study.

Assessment of the Disability Centrality Model

In the present study, a number of hypotheses related to the proposed model were tested among a sample of adults with MS. In order to fully assess the disability centrality model, it will be necessary to complete a longitudinal analysis of the proposed changes in the domain structure of a sample of individuals over time. Although such research is currently under way, the present analysis describes a cross-sectional analysis in which only a limited assessment of the complete model is possible. This analysis examines the existence of a number of hypothesized relationships that would be expected to exist at a point in time if indeed the model accurately portrays the ongoing process of adaptation. Specifically, the following hypotheses were evaluated:

1. Domain satisfaction and domain control mediate the relationship between illness impact and overall SQOL.

2. Domain importance moderates the relationship between domain satisfaction and overall QOL (i.e., satisfaction in more central domains has a greater influence on evaluations of overall SQOL than in more peripheral domains).

3. Overall SQOL, domain satisfaction, control, and importance are all negatively correlated with the level of perceived impact.

4. Subjective QOL scores would be correlated with scores on an existing measure of psychosocial adaptation, and

5. Self-management would be positively related to both perceived control, and as a result, QOL.

Method

Participants

The participants for this study were adults with MS who were on the mailing list of a chapter of the National Multiple Sclerosis Society (NMSS) located in the Southeastern United States. Participants were mailed the survey instrument, a letter of invitation, statement of informed consent, and a description of the study during the fall of 2004 and winter of 2005. To ensure participant anonymity, staff at the NMSS chapter were responsible for mailing the research packet on behalf of the researcher. A total of 350 surveys were mailed. A second mailing was conducted after 30 days. Forty-six envelopes were returned to the researcher as having an incorrect or undeliverable address, or having been sent to an individual who did not have MS. A total of 98 completed responses were returned, providing an effective response rate of 32%.

Instruments

Four research instruments were used in this study. These were the Delighted-Terrible Scale (Andrews & Withey, 1976), the Ladder of Adjustment (Crewe & Krause, 1990), the Disability Centrality Scale (Bishop, 2005a), and a self-management scale that was developed for this study.

Delighted-Terrible Scale. Overall QOL was measured using the Delighted-Terrible Scale (DTS). This single-item QOL rating scale consists of seven response categories, ranging from terrible (1) to delighted (7). The DTS has been used in hundreds of studies in the last three decades and has proved highly valid (Andrews & Robinson, 1991). In the present study, a Cronbach's coefficient alpha of .80 was calculated for the DTS.

Ladder of Adjustment. The Ladder of Adjustment is a 2-item scale and has been found to correlate (r = .71) with the Multidimensional Adjustment Profile (Crewe & Krause, 1990). Reliability analysis of the Ladder of Adjustment in the present study showed that the scale had an acceptable level (Nunally, 1978) of internal consistency (Cronbach [alpha] = .81). The Ladder was presented with the following introduction:
 Suppose that a person's overall adjustment to a disability
 or illness could be shown on a ladder having 10 steps
 with the tenth step representing the best possible
 adjustment and the first representing the worst possible.
 On what step of the ladder would you place yourself to
 indicate your current overall adjustment (1-10) (check
 one)? Where on the ladder do you expect yourself to be
 in 5 years (1-10)?


Disability Centrality Scale. The Disability Centrality Scale assesses the respondents' level of satisfaction, CIAD-related impact, and perceived control within 10 life domains, as well as the level of importance ascribed to each of the domains. The domains were identified based on a review of the literature and previous research by the first author (Bishop & Allen, 2003) and were selected as being those domains most frequently represented in multidimensional QOL instruments. The domains included the following (as phrased on the questionnaire): Physical Health, Mental Health (e.g., emotional well-being, happiness, enjoyment of life), Work (or studies), Leisure Activities (e.g., sports, hobbies, things you do to relax or have fun), Financial Situation, Relationship with your spouse (or partner if not married), Family Relations, Other Social Relations (e.g., friends, people who offer you support), Autonomy/independence (e.g., the ability to do the things you want, independence, freedom), Religious/Spiritual Expression (e.g., spiritual health, church life, relationship with God).

The participants responded to the following questions for each of the 10 domains based on a seven-point interval scale ranging from "Not very" to "Very" followed by the appropriate descriptor (e.g., Not very important"):

1. How important is this part of your life to your overall quality of life?

2. How satisfied are you with how this part of your life is going?

3. How much control do you have over changing this part of your life?

4. How much does your illness or disability and/ or its treatment impact your ability to function in this area of your life as you would like to?

Reliability analysis of the Domain Scale indicated that overall the scale had an acceptable level of internal consistency (Cronbach [alpha] = .74). The four component scales had the following alphas: satisfaction (Cronbach [alpha] = .88), control (Cronbach [alpha] = .84), impact (Cronbach [alpha] = .89), and importance (Cronbach [alpha] =.64).

Self-management Scale. In order to assess self-management, an 11-item scale was developed for this study through a review of the MS and self-management literature. The scale was designed to assess the participants' awareness of and engagement in MS-related self-management practices. The scale assessed the degree to which participants understood their medical treatments, communicated with health-care providers about their treatment, felt informed about and sought information about MS, and engaged in various health-promotion activities. A Cronbach's coefficient alpha of .68 was calculated for the scale.

Statistical Analysis

Descriptive and correlational analyses, and a series of multiple regression analyses were conducted to test the hypotheses of this exploratory study. Descriptive statistics were used to describe the model-variables. The mean ratings for domain satisfaction, domain importance, domain impact, and domain control were calculated and used to assess the model. Pearson correlation coefficients were calculated among the variables of interest. To assess the relationship between adaptation and QOL, correlations were computed between scores on the Ladder of Adjustment Scale and scores on two measures of QOL, the Delighted Terrible Scale and the mean of the participants' domain satisfaction ratings.

Tests of the proposed mediating role of satisfaction and control between impact of the CID and overall QOL were conducted using the method described by Baron and Kenny (1986). According to this method, three regression equations are estimated. First, the mediator is regressed on the independent variable; second, the dependent variable is regressed on the independent variable; and third, the dependent variable is regressed on both the independent variable and the mediator. In order to establish mediation, the independent variable must affect the mediator in the first equation; the independent variable must affect the dependent variable in the second equation, and the mediator must affect the dependent variable in the third equation. If in the third equation the effect of the independent variable on the dependent variable is less than in the second, mediation is established (Baron & Kenny). The Sobel test (Sobel, 1982) was also used to determine the indirect effect of the independent variable on the dependent variable through the mediator. This test determines the significance of any reduction in the effect of the independent variable on the dependent variable when the mediator is included in the model.

To assess the hypothesized moderating effect of domain importance between domain satisfaction and overall QOL, the regression with interaction procedure was used (Baron & Kenny, 1986). A moderator variable influences the relationship between a predictor variable and a criterion variable by affecting the strength or direction of the relationship. In the present model, it was hypothesized that the relationship between domain satisfaction and overall QOL is stronger at higher levels of the domain importance variable. Testing for a moderator effect involves a two-step multiple regression analysis. First, the predictor (domain satisfaction) and moderator (domain importance) main effects are regressed on the criterion variable. Second, the interaction term, representing the product of the two main effects, was entered into the equation. The moderator hypothesis is supported when the interaction is significant. Due to the manner in which the interaction is computed, the main effects are highly correlated with the interaction term and produce problematic multicollinearity effects. To eliminate these effects, the predictor and moderator variables were first centered, creating a variable in deviation score form with a mean of zero. This transformation has no impact on the level of significance of the interaction terms.

Prior to the multiple regression analyses, the variables were inspected to determine whether assumptions of normality and linearity were met. Although the model variables were negatively skewed, none of the skewness values exceeded +/- .70 and were therefore judged appropriate for further analysis (Tabachnick & Fidell, 2001). Due to correlations among the potential predictor variables, each regressor was normalized prior to entry into the regression models. Normalization minimizes the degree of association between the variables and reduces the likelihood that multicollinearity is distorting the estimated parameters (Cronbach, 1987).

Results

Participants

Eighty-four percent of the sample was female (n = 82). Participants identified their race/ethnicity as White (non-Hispanic) (n = 94; 96%), African American (n = 2; 2%), and Native American (n = 2; 2%). The average age of the participants was 48.7 (SD = 11.4) at the time of the study and 35.9 (SD = 9.1) at the time of onset. The average duration of the illness since onset was 12.8 years (SD = 8.6). Approximately 65% of the participants were married, 10% were widowed, 19% divorced, 1% separated, and 5% were never married.

All of the participants reported completing high school, 41% reported having some college or technical school, 34% reported being a college graduate, and 6% reported having a Master's degree of higher. With regard to employment, 32% were employed full-time, 7.2% part-time, 2.1% unemployed and looking for work, 7.2% unemployed but not currently looking for work, 5.2% were retired, 28.9% were on permanent disability, 16.5% were homemakers, and 1% were students. The median reported monthly household income was $2,500, with an evenly distributed range between less than $500.00 and over $4000 per month.

Inter- Variable Correlations

The results of the correlational analyses are presented in Table 1. All correlations were in the predicted direction. Adaptation to disability, as measured with the Ladder of Adjustment Scale was moderately correlated with overall QOL as measured using both the Delighted-Terrible Scale (r = .54, p = .001) and the mean of the domain satisfaction ratings (r = .63, p = .001). As hypothesized, perceived impact was negatively correlated with overall QOL (r = -.31, p = .001), domain satisfaction (r = -.42, p = .001), and domain control (r = -.40, p = .001). In addition, self-management was positively related to both perceived control, (r =.32, p = .001) and QOL (r = .27, p = .001).

Mediation Analysis

To test the mediating role of domain satisfaction between domain impact and overall QOL, domain satisfaction was first regressed on domain impact. This relationship was significant (p < .0001). Second, QOL was regressed on impact. This relationship was also significant (p = .002). Third, QOL was regressed on both domain impact and domain satisfaction. In this equation the relationship between satisfaction and QOL was significant (p < .0001), and the previously significant relationship between impact and QOL was no longer significant (p = .774). The Sobel test for this mediation model was significant (Sobel statistic = -4.01, p < .0001) further indicating the mediating role of satisfaction in the relationship between impact and QOL.

To test the mediating role of domain control between domain impact and overall QOL, control was first regressed on domain impact. This relationship was significant (p < .001). The second equation, in which QOL was regressed on impact was significant, as described above. Third, QOL was regressed on impact and control. In this equation the relationship between control and QOL was significant (p < .0001), and the previously significant relationship between impact and QOL was no longer significant (p = .540). The Sobel test for this mediation model was significant (Sobel statistic = -3.78, p < .0001), supporting the mediating role of control in the relationship between impact and QOL. The multiple regression analyses conducted to assess mediation are presented in Table 2.

Moderation Analysis

The test of the proposed moderating role of importance in the relationship between domain satisfaction and overall QOL was conducted using a two-step multiple regression analysis. In step one, domain satisfaction (path a) and domain importance (path b) main effects were entered into the regression equation. In step two, the interaction term, representing the product of the two main effects, was entered into the equation with the main effects (path c). The hypothesized moderating effect of importance was supported by the significant path from the interaction term to overall QOL (p = .053; B =.656), and by the significant change in [R.sup.2] when the interaction term entered the regression equation. The results of this analysis are presented in Table 3.

Discussion

The results of this study support the existence of the relationships proposed within the disability centrality model, including the mediating roles of satisfaction and perceived control between the impact of MS and QOL, and the hypothesized moderating role of domain importance between domain satisfaction and overall QOL. A statistically significant positive correlation was found between scores on the self-management scale and both perceived control and QOL. Finally, a statistically significant positive correlation was found between scores on the Ladder of Adjustment scale and both an existing measure of overall QOL, and QOL when represented as an aggregate of satisfaction across domains. These results support the contention that overall QOL represents an appropriate measure of psychosocial adaptation.

Although further research, including a longitudinal assessment of the proposed model is clearly necessary, based on the present findings a number of clinical implications for working with persons with MS are suggested by the present findings.

Clinical Implications

It has frequently been suggested that psychosocial adaptation, or the individual's adaptive response to living with chronic illness, is a critical factor in the success of the rehabilitation process (e.g., Affleck, Tennen, Pfeiffer, & Fifield, 1987; Kendall & Buys, 1998; Livneh, Martz, & Wilson, 2001). The correlation between QOL and psychosocial adaptation found in this and previous research (Bishop, 2005a) suggests that a comprehensive multidimensional QOL assessment, such as was used in the present study, can provide a valid and useful method of assessing psychosocial adaptation. Such an assessment can provide a clear picture of the client's experience across important life domains, and a means of prioritizing rehabilitation interventions. The present study also suggests that such an assessment is improved with the inclusion of a domain importance assessment.

The present findings with regard to the hypothesized mediating role of perceived satisfaction and control suggest two specific routes of clinical intervention that may result in increased client QOL. The first is interventions that enhance perceived control. Several forms of intervention have been proposed in this area and found to be effective. These include client education about the illness and its treatment, helping the client to develop self-management skills, assisting the client in identifying and implementing accommodations that allow increased control over his or her environment, and teaching time management and problem-solving skills (Corbin & Strauss, 1988; Endler, Kocovski, & Macrodimitris, 2001; Endler, Kocovski, & Macrodimitris, 2001). The evidence of a correlation between self-management and the broader concept of multidimensional control also has significant clinical implications. It may suggest that engaging in self-management practices and illness-education promotes feelings of personal control across a number of domains. Of course, because a causal relationship cannot be assumed (i.e., it may be the case that persons with higher levels of personal control are more likely to engage in self-management) longitudinal assessment of this relationship is necessary.

The second route amenable to clinical intervention involves assisting the client to expand his or her perspective about the means of attaining satisfaction. For example, when previously satisfying activities can no longer be engaged in, the counselor can educate the client about alternative ways of achieving satisfaction in the same domain, by learning new ways of participating. Alternately, the counselor may assist the individual to explore new interests, new social outlets, and new ways of engaging life such that clients learn to find satisfaction in previously peripheral domains.

The present study has a number of limitations that should be considered in interpreting the results. The sample was geographically and demographically restricted, with only a small proportion of respondents from racial or ethnic minority backgrounds. The response rate was also relatively low. Internal validity was threatened by the operationalization of the variables in the study. Quality of life, satisfaction, control, and impact are all broad constructs that may be assessed by numerous other means.

Conclusion

Understanding the impact of MS and other chronic illnesses on QOL and psychosocial adaptation is a critically important rehabilitation goal. The model assessed in this study provides a potentially useful approach to improved understanding and clinical intervention. Although further research with the model is clearly needed, the results of this study provide a number of directions for clinical intervention, and particularly highlight the importance of self-management knowledge and behaviors in reducing the impact of MS on QOL.

Admittedly, this model of the conditions for maintaining satisfaction and psychosocial well-being provides a rather mechanistic and mathematical view of what is in reality a much messier and more complicated reality. The idea, for example, that high satisfaction in a highly central domain may, by extension of the theories behind this model, negate dissatisfaction in two domains that are half as important appears to suggest that complex experiences may be reduced to a series of mathematical equations. The methodology and measurement techniques currently employed to assess such concepts as satisfaction and importance are not well-aligned with the sort of highly fluid and complex weighting that occurs in the human mind.

However, despite its simplistic and analytical nature, so apparently incongruous with reality, the ideas underlying the model do appear to have basis in the machinations of adaptive cognitions and behavior. There is evidence from the present and previous research with this model, for example, that the level of satisfaction in more important domains does indeed have a stronger relationship with overall QOL than satisfaction in less important domains. There is evidence, from research with this model as well as with the illness intrusiveness model, that the impact of chronic illness on one's QOL is mediated through indirect mechanisms; by reducing domain-based satisfaction and one's sense of control over reducing this impact. And because this evidence has broad implications for continued theory development, for enhanced understanding, and for preventive and curative interventions, further investigation of the model and its underlying ideas is warranted.

Acknowledgements

We would like to gratefully acknowledge the assistance of Doug Dressman (President), Sonya Sandridge (Director of Chapter Programs), and the staff and volunteers of the National Multiple Sclerosis Society- Kentucky-Southeast Indiana Chapter. This research would not have been possible without their help and commitment to improving the lives of persons with multiple sclerosis.

This research was made possible through the generous support of the Arvle and Ellen Turner Thacker Research Endowment.

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Malachy Bishop

Department of Special Education and Rehabilitation

Counseling at the University of Kentucky

Donald M. Stenhoff

Department of Special Education and Rehabilitation

Counseling at the University of Kentucky

Lindsey Shepard

Department of Special Education and Rehabilitation

Counseling at the University of Kentucky

Malachy Bishop, Ph.D., Rehabilitation Counseling Program, 220 Taylor Education Building, University of Kentucky, Lexington, KY, 40506. Email: mbishop@uky.edu
Table 1. Intercorrelations among Study Variables

Variable (1) (2) (3)

(1) QOL --
(2) Ladder .535 ** --
(3) Importance .308 ** .260 * --
(4) Satisfaction .707 ** .632 ** .397 **
(5) Control .673 ** .594 ** .260 *
(6) Impact -.314 ** -.399 ** -.205
(7) Self-Mgmt .272 * .268 * .232

Variable (4) (5) (6)

(1) QOL
(2) Ladder
(3) Importance
(4) Satisfaction --
(5) Control .815 ** --
(6) Impact -.417 ** -.403 ** --
(7) Self-Mgmt .391 ** .317 ** -.344 **

Note. QOL = Delighted-Terrible Scale (Andrews & Withey, 1976); Ladder
= Ladder of Adjustment Scale (Crewe & Krause, 1990); Importance,
Satisfaction, Control, and Impact = mean scores across domains on the
Disability Centrality Scale; Self-Mgmt = mean score on self-management
scale.

** p < .01, * p < .05

Table 2. Tests of Domain Satisfaction and Domain Control as Mediating
Variables between Domain Impact and Overall QOL

Dependent Independent [R.sup.2. B SE p
Variable Variable sub.cum]

 Analysis 1

Step
1. Domain Domain Impact .174 -.356 .079 .0001
 Satisfaction
2. Overall QOL Domain Impact .100 -.267 .082 .002
3. Overall QOL Domain Impact -.020 .068 .774
 Domain .500 .694 .079 .0001
 Satisfaction

 Analysis 2

Step
1. Domain Control Domain Impact 162 -.323 .075 .0001
2. Overall QOL Domain Impact .100 -.267 .082 .002
3. Overall QOL Domain Impact -.043 .070 .540
 Domain Control .455 .692 .088 .0001

Table 3. Test of the Moderating Effect of Importance between Domain
Satisfaction and QOL

Predictor B SE [R.sup.2. [R.sup.2] Significance
Variables sub.cum] Change of F Change

Step 1.
 Satisfaction .592 .103
 Importance .083 .105 .373 .373 .0001

Step 2.
 Satisfaction .285 .186
 Importance .352 .244
 Satisfaction .656 .334 .405 .032 .053
 X Importance
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