Research paperProfiles of quality of life in opiate-dependent individuals after starting methadone treatment: A latent class analysis
Introduction
Quality of life (QoL) has become an important outcome measure and useful assessment tool in health care for individuals suffering from chronic illnesses (Higginson and Carr, 2001, Katschnig, 2006). Recent recognition that addiction is a chronic disorder and – consequently – requires a continuing care and support approach has resulted in growing attention to QoL in substance abuse research, mainly among opiate users (McLellan, 2002, Zubaran and Foresti, 2009). The rather limited and late attention to QoL in substance abusers contrasts sharply with studies on other chronic illnesses, such as cancer and schizophrenia, in which improved QoL is regarded as an important treatment objective (Sanders, Egger, Donovan, Tallon, & Frankel, 1998). Due to the related health and socio-economic consequences of substance dependence, most outcome studies in substance abuse research focus on aspects such as abstinence of illegal drugs, reducing the health risks involved with drug use, and the absence of criminal involvement. Limited consideration is given to outcomes important for opiate-dependent individuals themselves (Fischer et al., 2005, Ruefli and Rogers, 2004). This unilateral focus on socially desirable outcomes is inappropriate if one wants to take person-centred outcomes such as QoL into account (Fischer et al., 2005, Hagenow, 2003).
QoL is a broad, encompassing concept influenced by an individual's expectations and personal perspective, which can only be judged by the person him/herself (Allison et al., 1997, Parse, 2007). The importance or weight people attach to various dimensions or domains of QoL can differ greatly between individuals and within groups, based on their individual values and priorities, and can fluctuate through their personal course of life (Carr and Higginson, 2001, Carr et al., 1996). The focus in QoL is not only on health aspects, but it represents a wide range of life domains (e.g. self-determination, leisure and social participation, self-esteem, finances) important for an individual's life (Holmes, 2005, Schalock, 1996). Consequently, the multidimensionality of the concept QoL, together with the individualistic nature of the construct, may result in a strong heterogeneity and variation in QoL scores between individuals.
Most studies on QoL in substance abuse research are based on average QoL scores of a specific sample to demonstrate preferences of the whole group. By doing so, potential heterogeneity (inter-individual variability) within the population is ignored. Mean scores do not differentiate sufficiently and lack information on the diversity of results starting from an individual level, resulting in a loss of relevant information. Latent class analysis (LCA) is a type of modelling with categorical latent variables that gives attention to the heterogeneity of individual response patterns and defines unique subgroups in a sample (de Dios et al., 2010, Monga et al., 2007, Moss et al., 2007, Muthén and Muthén, 2000). The different subgroups in latent classes are not known in advance, as in a variable-centred approach, but are directly derived from the complete dataset based on individual responses (Muthén & Muthén, 2000). A study on illegal opiate users in Canada using LCA demonstrated that various subgroups of illegal opiate-users could be distinguished in terms of co-occurring drug use, comorbidity, and living situation (Monga et al., 2007). A recent study of Schand, Slade, Degenhardt, Baillie, and Nelson (2010) illustrated that opiate dependence can be divided in two distinct classes based on severity of dependence, with a higher risk of externalising disorders when the severity of opiate dependence increases. Furthermore, research has demonstrated that large differences exist between opiate-users in the community and those seeking treatment; however, large differences in the group seeking help were also noticeable (Eland-Goossensen et al., 1997, Schand et al., 2010). Variation in the QoL of different groups of opiate-dependent individuals in substitution treatment (e.g. presence or absence of comorbidity, gender differences) has been demonstrated in various studies (Bizzarri et al., 2005, De Maeyer et al., 2010, Fassino et al., 2004, Giacomuzzi et al., 2005). However, research on heterogeneity in a specific sample of opiate-dependent individuals is lacking, though such heterogeneity can have a large impact on the individual client and on the generalization of results (Donaldson & Moinpour, 2002).
Consequently, the aim of this study is to examine the response patterns concerning QoL of a sample of opiate-dependent individuals who started methadone treatment five to ten years ago. Given the fact that different groups of clients with their own specific needs and characteristics appeal to methadone treatment and the strong subjective character of QoL, heterogeneity in the QoL scores of opiate-dependent individuals can be expected (Bonomi et al., 2000, De Maeyer et al., 2011a, Fischer et al., 2005, Gourlay et al., 2005). The focus of the present study is to identify classes of opiate-dependent individuals with different QoL profiles. The following research questions were formulated:
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Which patterns of QoL can be distinguished in opiate-dependent individuals five to ten years after starting methadone treatment?
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Are these QoL-patterns related to socio-demographic, drug-, health- and person-related variables?
Section snippets
Study sample and design
This study was set up as a cross-sectional study on the current QoL of a cohort of opiate-dependent individuals who started outpatient methadone treatment in the region of Ghent (Belgium) between 1997 and 2002. This time frame was chosen because the first medical-social care centre for outpatient methadone treatment was opened in 1997 and we intended to monitor the current situation of opiate-dependent persons who started methadone treatment during the first six years. It has been estimated
Sample characteristics
Respondents were predominantly male (74.8%), with an average age of 36.6 years (SD = 7.5). The mean duration of methadone treatment was 7.6 years (SD = 4.4). A high proportion of the sample (86.5%) had followed at least two methadone treatment episodes. Almost three-quarters of the sample (74.2%) was currently still on methadone. Half of the participants (49.7%) reported recent heroin use and 54.1% scored above the clinical cut-off score for overall psychopathology (cf. Table 1).
Latent class analysis
Fit statistics were
Discussion
This is the first study to investigate different profiles of QoL among opiate-dependent individuals and their relatedness with socio-demographic, drug-, health- and person-related variables. The findings of our study support the existence of three distinct classes of QoL among opiate-dependent individuals five to ten years after starting methadone treatment and provide a better understanding of the heterogeneous character of QoL.
Conflicts of interest
None.
Acknowledgement
We would like to acknowledge the Special Research Fund of Ghent University, Belgium, for funding this study.
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