Measuring quality of life in opioid-dependent people: a systematic review of assessment instruments
Measuring quality of life in opioid-dependent people: a systematic review of assessment instruments
Lisa Strada 0 1 2 3 4 5 6 7 8 9
Wouter Vanderplasschen 0 1 2 3 4 5 6 7 8 9
Angela Buchholz 0 1 2 3 4 5 6 7 8 9
Bernd Schulte 0 1 2 3 4 5 6 7 8 9
Ashley E. Muller 0 1 2 3 4 5 6 7 8 9
Uwe Verthein 0 1 2 3 4 5 6 7 8 9
Jens Reimer 0 1 2 3 4 5 6 7 8 9
0 Angela Buchholz
1 Wouter Vanderplasschen
2 & Lisa Strada
3 Gesundheit Nord , Kurfu ̈rstenallee 130, 28211 Bremen , Germany
4 Norwegian Centre for Addiction Research, Institute of Clinical Medicine, University of Oslo , Pb 1039 Blindern, 0450 Oslo , Norway
5 Department of Medical Psychology, University Medical Centre Hamburg-Eppendorf , Martinistrasse 52, 20246 Hamburg , Germany
6 Department of Special Needs Education, Ghent University , Henri Dunantlaan 2, 9000 Ghent , Belgium
7 Uwe Verthein
8 Ashley E. Muller
9 Bernd Schulte
Purpose Opioid dependence is a chronic relapsing disorder. Despite increasing research on quality of life (QOL) in people with opioid dependence, little attention has been paid to the instruments used. This systematic review examines the suitability of QOL instruments for use in opioid-dependent populations and the instruments' quality. Methods A systematic search was performed in the databases Medline, PsycInfo, The Cochrane Library, and CINAHL. Articles were eligible if they assessed QOL of opioid-dependent populations using a validated QOL instrument. Item content relevance to opioid-dependent people was evaluated by means of content analysis, and instrument properties were assessed using minimum standards for patient-reported outcome measures.
Centre for Interdisciplinary Addiction Research, University
Medical Centre Hamburg-Eppendorf, Martinistrasse 52,
20246 Hamburg, Germany
Keywords Quality of life Opioid Instrument Review
Content analysis Substance use disorder
Opioid dependence is a chronic relapsing disorder with the
greatest disease burden of all illicit drugs [
] and the
highest demand for treatment [
]. People dependent on
opioids not only suffer from adverse health outcomes and
high rates of overdose and overdose deaths [
], but they
also often experience negative socioeconomic
consequences, social marginalization, and serious long-term
impairments in nearly every realm of their lives [
Harm reduction programs, such as opioid substitution
treatment (OST), are therefore important strategies to
reduce the harm of unsafe drug use and the detrimental
consequences of drug dependence [
]. OST is a
pharmacological treatment preferably administered in combination
with psychosocial support, which aims to stabilize patients’
health and enhance their wellbeing [
]. However, the focus
in research and clinical practice tends to be on socially
desirable outcomes, such as reduced drug use, as opposed
to outcomes that are important to the patients themselves,
such as their personal wellbeing. Quality of life (QOL)
lends itself as a useful parameter to measure the impact of
opioid dependence on daily life and to evaluate the quality
and success of treatment and harm reduction programs,
based on patients’ subjective experiences [
QOL refers to an individual’s perception of their
position in life in relation to their goals, expectations,
standards, and concerns [
]. While patient-reported outcomes
(PROs), such as QOL, are widely recognized as valuable
outcome measures in treatment [
], the field of opioid
dependence is lagging behind in this regard. PROs are
outcomes directly reported by the patients themselves, in
contrast to clinical outcomes or clinician- or
proxy-reported outcomes. In opioid dependence, objective
outcomes, such as abstinence from opioids and the reduction
of other drug use are generally considered primary
measures of treatment success . Yet few opioid-dependent
patients achieve sustained abstinence [
] and continued
drug use is not necessarily an indicator of poor QOL [
Moreover, it is impaired QOL that seems to instigate
treatment uptake rather than a desire to reduce drug use per
], and research shows that enhanced QOL may
sustain remission [
]. Taken together, this underlines the
importance of including QOL as a complementary
The multidimensional concept of QOL is distinct from
health-related quality of life (HRQOL). While HRQOL
includes physical, psychological, and social domains of
], QOL also encompasses life domains beyond
]. Given the wide-ranging impact of opioid
dependence on people’s lives [
], the concept of
HRQOL is limited for use in drug users, providing only a
unilateral perspective of their wellbeing . Researchers
have been advocating the use of QOL as opposed to
HRQOL measures in opioid dependence research, stressing
the need for a holistic and integrative approach to treatment
16, 22, 23
Over the past two decades, there has been increasing
research on QOL in opioid-dependent people. A systematic
review demonstrated that until 2009, fifteen HRQOL and
QOL instruments had been used in 38 studies on people
with opioid dependence and about half of the studies used
HRQOL rather than QOL instruments [
heterogeneity of tools hampers our ability to compare study
outcomes, and the use of HRQOL tools provides a limited
view on drug users’ QOL. (Here, tool is synonymous with
instrument.) A further methodological concern that limits
our ability to generalize study findings is the use of
different types of instruments. QOL instruments can be
generic or disease specific. Generic tools allow for
comparisons across populations, while disease-specific
tools measure aspects that are relevant to a specific
population. Instruments can also be uni- or multidimensional.
Unidimensional measures provide a global assessment of
QOL (e.g., ‘How satisfied are you with your life as a
whole?’) whereas multidimensional measures assess
satisfaction with multiple life domains.
While research shows that the QOL of opioid users both
in and out of treatment is significantly lower compared to
the general population [
], it is unclear to what extent
QOL instruments capture aspects of QOL that are relevant
to people with opioid dependence, and whether they are
valid and reliable measures for this population. An
evaluation of tools is now of utmost importance, because the
continued employment of heterogeneous, possibly
ill-suited QOL instruments may affect the interpretability and
comparability of study outcomes and hinder further
advancements in the field [
This comprehensive systematic review examines the
suitability and quality of QOL instruments for use in
people with opioid dependence. The scope of this review is
limited to illicit opioid dependence (including patients in
substance use treatment, such as OST) and does not include
prescription opioid dependence (e.g., chronic pain), as we
focus on the context of illegal drug use. We identify QOL
instruments that have been used in opioid-dependent
populations to date and evaluate the item content relevance to
this population, as well as the instruments’ properties (e.g.
conceptual and measurement model, psychometric
properties). In line with expert recommendations that the way
forward in opioid dependence research is a holistic and
multidimensional approach to QOL [
], HRQOL tools
and single-item measures are excluded from this review.
A systematic review of QOL instruments was conducted
using an adaptation of the PRISMA guidelines (Preferred
Reporting Items for Systematic Reviews and Meta-analysis
). We evaluated the item content relevance of
instruments by examining the extent to which items reflect QOL
domains that are important to opioid-dependent people
(indicating ‘suitability’). We also assessed the properties of
instruments using recommended minimum standards that
PRO measures must meet to be considered suitable for use
in scientific studies (indicating ‘quality’).
Search strategy and inclusion criteria for articles
A comprehensive literature search was performed on 16
March 2017 in the databases MEDLINE (OVID),
PsycINFO, The Cochrane Library, and CINAHL (EBSCO).
The search strategy included four categories of keywords:
(i) quality of life, (ii) instrument, (iii) drug addiction, and
(iv) opioids (see Online Resource 1). Reference lists of
relevant articles and reviews were screened, a manual
Internet search was performed, and colleagues were
consulted to identify additional literature and instruments.
Authors of articles that could not be accessed were
contacted for missing information.
Inclusion criteria for articles were as follows: (1) The
QOL of individuals with opioid dependence was assessed.
Studies about people with other substance use problems or
chronic diseases were included if opioid dependence was
present among a subsample of the study and if a QOL
outcome was reported for that opioid-dependent sample, or
for a mixed drug user sample if at least half was opioid
dependent. (2) A validated QOL instrument was used. (3)
QOL was self-reported by opioid-dependent individuals.
(4) Articles were published between 1990 and 2017. This
time limit was set, because QOL research in opioid
dependence only began in the 1990s. No language
restrictions were applied to the search. All identified
references were independently reviewed by two of the authors
Assessment of item content relevance
Instrument items need to be comprehensive and measure
important aspects of a target population’s QOL [
therefore assessed the extent to which instrument items
measure QOL domains that have been found relevant to
opioid-dependent populations (i.e., a kind of face validity
assessment). We used the QOL model of Schalock [
which was developed for people with intellectual
disabilities, but has also been found relevant to opioid-dependent
], people with mental health problems
], and other social service recipients [
adopted a sociopolitical perspective, defining quality of life
as the promotion of equal opportunities for people with
different needs [
]. This makes the model especially
useful for studying marginalized populations. The
theoretical framework was derived from an extensive review of
the QOL literature and consists of eight core domains:
emotional wellbeing, interpersonal relations, physical
wellbeing, material wellbeing, personal development,
selfdetermination, social inclusion, and rights. While the
former four domains are common among models of QOL, it is
the latter four that distinguish Schalock’s model. These
domains relate to issues of autonomy, social exclusion, and
discrimination, which are more pertinent to marginalized
populations than to the general population [
propose that if an instrument is to adequately and
comprehensively assess the QOL of opioid-dependent
individuals, each of Schalock’s QOL domains should be
represented by at least one item.
The content of QOL instruments was systematically
differentiated by content analysis (as seen in a study by Van
]). Four researchers (BS, AB, AM, LS)
independently coded the instrument items using MAXQDA
software for qualitative data analysis. Each item was
assigned to one of Schalock’s eight QOL domains or an
additional code ‘global quality of life.’ The latter code was
added because instruments often include items that measure
QOL on a global scale. Differences in codings were
discussed, iteratively, until consensus was reached. Decision
rules that were developed during the discussions include:
Code for meaning, rather than the exact words
When an item asks about ‘satisfaction with X,’ code X
rather than emotional wellbeing (‘satisfaction’)
When items are subdivided by domains in the original
instrument, do not automatically code items as the
When the instrument instructions say to consider an
item in a certain context, also consider that context
Code ‘global quality of life’ when an item refers to life
as a whole or when it can be understood in terms of any
of the eight domains
Finally, we compared our codings to the original
instrument domains reported in the instrument
development papers (see Online Resource 2). This comparison
loosely served as a measure of external validity, based on
the premise that the distribution of codings should not
differ excessively from the original domains.
A QOL instrument should describe the population it is intended for
A QOL instrument should describe (i) the conceptual model including how the authors
define the concept of QOL or the theoretical framework within which the tool is
developed, and (ii) the measurement model including evidence for the dimensionality of
Items should be generated with patient input and instruments should be piloted tested
A QOL instrument should have low respondent and administrator burden. We examine the
mode of administration, the number of items and domains, and completion time
The scores of a QOL instrument should be easy to interpret: (i) there should be
information on what high and low scores represent, and (ii) norm values should be
We report the availability of instruments in different languages
Instruments should have evidence of good responsiveness, internal consistency reliability,
construct validity (e.g., convergent and discriminant validity), and content validity in the
target population of the research application (here: opioid-dependent people)
Assessment of instrument properties
We assessed the instrument properties using recommended
minimum standards for PRO measures developed by the
International Society of Quality of Life (ISOQOL).
Experienced members of the ISOQOL identified minimum
standards for the design and selection of PRO measures
that instruments must meet to be considered suitable for
use in scientific studies [
]. These recommendations are
near identical to the suggested guidelines of the Scientific
Advisory Committee of the Medical Outcomes Trust from
15 years ago, underlining the importance and timelessness
of these properties [
]. Given that we evaluate the
instruments’ suitability for use in opioid-dependent people,
we reviewed the psychometric properties when instruments
were used in opioid-dependent populations. In addition to
the minimum standards, we examined the methodology
used to develop the instruments. Methodological rigor is an
important aspect in the development of a good PRO
measure and yet it appears that few instruments follow
systematic ‘gold standard’ development procedures [
Five properties were examined at a descriptive level
(target population, mode of administration, number of
items and domains, completion time, availability of
languages) and six properties were evaluated using assessment
criteria (conceptual and measurement model, instrument
development methodology, interpretability of scores,
responsiveness, reliability, validity). A description of the
eleven properties as operationalized in this systematic
review is presented in Table 1. Assessment criteria were
concretely defined to enhance the inter-rater reliability
A data extraction table was used to compare the
instrument properties. Two investigators (AM, LS)
extracted the relevant information independently in
duplicate. Most information was extracted from the instrument
development and validation papers, and the instrument
manuals. Psychometric properties for opioid-dependent
populations were extracted from the 94 studies identified in
our literature search. Translations and norm values were
found by carrying out an additional search of the literature.
Three authors (AB, AM, LS) independently rated the
properties and disagreements were discussed until
consensus was reached.
In total, 581 articles were retrieved. Of those, 487 were
excluded because they did not assess QOL among people
dependent on illicit opioids (n = 281), they used HRQOL
tools, non-validated QOL tools, or single-item QOL tools
(n = 186), or they did not report a QOL outcome for an
opioid-dependent sample (n = 20). Thus, 94 articles used
instruments to assess self-reported QOL among
opioiddependent individuals (Fig. 1).
Among the 94 articles, we found 22 differently named
instruments, which could be grouped into 16 distinct
instruments (Table 3). Measuring instruments were
grouped if their content was the same, such as translations,
adaptations with a few different items, or different
temporal forms of items. WHOQOL-BREF was the most
frequently used tool (57 articles), followed by
LQoLPmodified in 10 articles, IDUQOL, SWLS, and PWI in 4
articles each, and 11 other instruments in 1–3 articles each.
The instruments were developed between 1977 and 2003,
a Standardized Response Mean
b Responsiveness and reliability: When values are reported for multiple items or domains, at least half of the items or domains must be at or
above the minimum acceptable value, to rate the property a ‘2’
ten in the English language and six in a foreign language
(LQoLP-modified in Dutch, MSQOL in German, SQLP
and TEAQV in French, EBP in Spanish, QOL-DA in
Chinese). Thirty-seven articles (39%) were based on
studies conducted in Asia (14 in Taiwan, 7 in China, 7 in
Malaysia, 6 in India, 3 in Vietnam), 35 articles (37%) were
from Europe, 8 articles from Australia, 6 articles from the
United States and Canada, 7 articles from the Middle East,
and one article was based on a study conducted in multiple
countries around the world.
Of the sixteen instruments, six were excluded from
analysis, because they could not be retrieved (SQLP,
Q-LES-Q), they were not available in the authors’ native or
professional languages English, German, or Dutch
(TEAQV in French, EBP in Spanish, QOL-DA in Chinese),
or the instrument had already been abandoned by the
author due to major flaws (ComQol [
]). A total of ten
instruments were included in the analysis. We assessed the
most frequently used version of each instrument, which
was incidentally also the most recently developed version.
The 341 items of the 10 instruments were assigned to
Schalock’s eight QOL domains or a global QOL category.
Four independent coders initially agreed on 71% of the
items. Coding agreement was highest for the domain’s
emotional wellbeing, physical wellbeing, interpersonal
relations and material wellbeing. Figure 2 presents
information on the QOL domains captured by each instrument.
Overall, the domain’s emotional wellbeing, interpersonal
relations, physical wellbeing, and material wellbeing were
coded more frequently across instruments than the other
four domains. Global QOL items were found in six
instruments. Only two instruments, LQoLP-modified and
IDUQOL, include at least one item on each of Schalock’s
eight domains. The five least-frequently used tools
(MSQOL, QOLI, QOLI-BV, MQOL, QLQ) have no items
on social inclusion and/or rights. WHOQOL-BREF, PWI,
and QLQ do not assess self-determination.
Instruments vary greatly in their item content focusing
on different QOL domains. WHOQOL-BREF comprised
42.3% and MSQOL comprised 30.5% physical wellbeing
items, followed by emotional wellbeing (WHOQOL-BREF
11.5%; MSQOL 28.8%) and interpersonal relations
(WHOQOL-BREF 11.5%; MSQOL 22.0%). Both
instruments include fewer or no items in the remaining domains.
LQoLP-modified and IDUQOL are the only two
instruments that comprised at least one item in each of
Schalock’s eight QOL domains. LQoLP-modified focuses
more on emotional wellbeing (25.4%), interpersonal
relations (14.4%), material wellbeing (16.1%), and
selfdetermination (19.5%), and has only 1 out of 118 items
relating to social inclusion. IDUQOL focuses on the social
domains (interpersonal relations 23.8%; social inclusion
23.8%), while items are evenly distributed for the
remaining domains (4.8–9.5%).
SWLS measures exclusively global QOL. QOLI has 1–4
items on each domain except rights, and measures more
interpersonal relations, social inclusion, and material
wellbeing (3–4 items) than the other domains (1–2 items).
QOLI-BV has a large percentage of items pertaining to
material wellbeing (40.3%), followed by physical
wellbeing (19.4%), interpersonal relations (17.7%), and up to
9.7% on the remaining domains. MQOL measures
emotional wellbeing (37.5%), followed by physical wellbeing
(25.0%), and 0 to 2 items on the remaining domains.
The domain distribution of PWI and QLQ must be
interpreted with caution due to the small number of items
(8 and 10, respectively). PWI items are evenly distributed
across domains with about 1 item per domain. QLQ
includes 1–3 items per domain, with a greater focus on
interpersonal relations and physical wellbeing, and no
items on self-determination, social inclusion, and rights.
As a measure of external validity, our codings were
compared to the original instrument domains. We found
that the original domains were mostly reflected in our
codings. For instance, over 80% of MSQOL items were
coded emotional wellbeing, physical wellbeing, or
interpersonal relations. Similarly, most of MSQOL’s original
domains pertained to those life domains. However, there
were also differences to the original domains. Over 40% of
WHOQOL-BREF items were coded physical wellbeing,
which differs from the original WHOQOL-BREF domains,
in which ‘physical health’ is one of four domains (i.e.,
25%). This suggests that WHOQOL-BREF has a greater
focus on health than indicated by the original domains.
Characteristics of the ten QOL instruments are presented in
Table 4. Four generic tools (WHOQOL-BREF, SWLS,
PWI, QOLI) and six disease-specific tools were identified,
of which four are for mental health care populations
(LQoLP-modified, MSQOL, QOLI-BV, QLQ), one for
people with life-threatening or terminal illness (MQOL),
and one for injection drug users (IDUQOL). Seven tools
are in questionnaire format and three are applied as
structured interviews (LQoLP-modified, IDUQOL, QOLI-BV).
Most tools contain 5–26 items measuring QOL, whereas
MSQOL, QOLI-BV, and LQoLP-modified contain 48, 74,
and 133 QOL items, respectively. Thus, two of the three
Instrument abbreviation (number of articles the instrument was used Instrument and reference
Note that two articles used two QOL instruments each [
a Similar versions grouped under WHOQOL-BREF: (i) WHOQOL-BREF (n = 39) was used in eleven languages: Malay, Chinese, Hindi,
Persian, Vietnamese, Slovenian, Slovak, Spanish, German, English, Italian; (ii) WHOQOL-BREF-Taiwanese version (WHOQOL-BREF-TW,
n = 13)
b Similar versions grouped under LQoLP-modified: (i) Lancashire Quality of Life Profile-modified (LQoLP-modified, n = 3), (ii) Berlin Quality
of Life Profile (Berliner Lebensqualita¨tsprofil, BELP, n = 6), (iii) Manchester Short Assessment of Quality of Life (MANSA, n = 1)
c Similar versions grouped under IDUQOL: (i) Injection Drug User Quality of Life Scale (IDUQOL, n = 3), (ii) Drug User Quality of Life Scale
(DUQOL, n = 1)
d Similar versions grouped under SWLS: (i) Satisfaction With Life Scale (SWLS, n = 2), (ii) Temporal Satisfaction With Life Scale (TSWLS,
n = 1), (iii) Temporal Satisfaction With Life Scale - present (TSWLS-present, n = 1)
e The tools examined in this review are taken from the instrument development articles referenced in Table 1, except if the most frequently used
version of an instrument differed from the original. We examined (i) the 21-item IDUQOL from Hubley and colleagues , instead of the
17-item version from Brogly and colleagues [
], (ii) the 16-item QOLI from Frisch [
], instead of the earlier 17-item version from Frisch and
], (iii) the 59-item MSQOL that we received from the author, instead of the version from Pukrop and colleagues [
], and (iv) the
16-item MQOL from Cohen and colleagues [
], instead of the earlier 17-item version from Cohen and colleagues [
* Instruments marked with an asterix are excluded from further analyses
tools in interview format are also the longest tools
(LQoLP-modified and QOLI-BV).
Completion time was only reported for half the tools and
ranged from 10–35 min (IDUQOL, QOLI, QOLI-BV,
MQOL) and 45 min for LQoLP-modified. Four tools are
available in more than 16 languages (WHOQOL-BREF,
SWLS, PWI, MQOL), five tools in English and up to 4
other languages (IDUQOL, MSQOL, QOLI, QOLI-BV,
QLQ), and LQoLP-modified is available in Dutch and
The conceptual and measurement model are described in
nearly all tools, except MSQOL, QOLI, and QLQ, which
lack a description of the conceptual model or evidence for
the dimensionality, or both. Instrument development
methodologies vary greatly between tools. For the three
most frequently used instruments (WHOQOL-BREF,
LQoLP-modified, IDUQOL) and QLQ, items were
generated with input from the target population and the
instrument was piloted. For PWI, QOLI-BV, and MQOL, items
were generated with target population input or they were
piloted. The remaining tools were developed from
alreadyexisting instruments or a review of the literature, and they
were not piloted. The interpretability of outcomes is high in
WHOQOL-BREF, SWLS, PWI, and QOLI, with
information on what high and low scores represent and available
normative values, while the other six tools lack normative
Data on psychometric properties for opioid-dependent
populations were scarce and incomplete. Psychometrics of
five instruments (WHOQOL-BREF, IDUQOL, PWI,
MSQOL, QOLI-BV) was tested in nine studies, of which
five were on WHOQOL-BREF. Responsiveness was only
assessed for WHOQOL-BREF and yielded mixed
evidence, with one study demonstrating above moderate effect
sizes (Cohen’s d C 0.50 for all four WHOQOL-BREF
domains) and another study failing to reveal any significant
changes over time (below moderate effect sizes: Cohen’s
d \ .50 for all four domains). Reliability was above the
minimum acceptable value for internal consistency for five
instruments (all Cronbach’s a C .70); no information on
reliability was reported for the other five instruments.
Content validity was not tested in any tool. Construct
validity was assessed in four instruments
(WHOQOLBREF, IDUQOL, MSQOL, QOLI-BV) although evidence
varies. Three studies demonstrated acceptable or marginal
goodness-of-fit of WHOQOL-BREF (via Rasch Analysis
or Confirmatory Factor Analysis), but with misfit items,
new emerging domains, or only a good fit after making
adjustments to the questionnaire. One study demonstrated
adequate fit indices for IDUQOL (GFI = .92; CFI = .97;
RMSEA = .044). Adequate convergent and discriminant
validity was demonstrated for MSQOL (moderate and low
correlations with a range of variables), and evidence of
convergent and discriminant validity of QOLI-BV was
suggested by moderately high and low correlations,
Finally, we examined whether instruments include
subjective and/or objective items. While QOL comprises
both subjective and objective components, the subjective
component prevails and research tends to focus
increasingly on QOL as a subjective concept [
]. We found that
seven instruments assess exclusively subjective QOL,
while three instruments assess both subjective and
objective QOL. LQoLP-modified and MSQOL consist about
one-third and QOLI-BV more than half of objective items.
Objective items include ‘‘Do you have a paid job?’’
(LQoLP-modified) and ‘‘What is your current living
situation?’’ (QOLI-BV), whereas subjective items include
‘‘How satisfied are you with your income?’’
(LQoLPmodified) and ‘‘How do you feel about the living
arrangements where you life?’’ (QOLI-BV).
Despite increasing use of QOL measures in studies on
opioid-dependent people, no suitable QOL instrument is
available to date. When selecting an instrument, both its
quality and content are important considerations. Yet, no
instrument in this review scored perfectly on the
recommended minimum standards for PRO measures and
comprehensively assessed QOL according to Schalock’s model
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]. Only IDUQOL and LQoLP-modified had good
item content relevance. However, their high respondent
and administrator burden (interview format, long
completion time) make them less practical for repeated use in
research and routine patient care. Moreover, they had little
evidence of good psychometric properties in opioid users.
On the other hand, WHOQOL-BREF was the only tool that
scored adequately on the properties, but its item content
focuses on physical health, thereby providing a limited
view of drug users’ QOL. This is a critical observation
because the majority of studies in this review used
WHOQOL-BREF. Other instruments have further
limitations. For instance, SWLS is a measure of global QOL and
so does not provide a multidimensional assessment of
QOL, and QOLI-BV assesses largely material wellbeing,
thus providing limited insight into individuals’ overall
The strength of this review lies in its structured approach
to the instrument evaluation using a theoretical framework
and well-established standards for PRO measures. Results
highlight limitations in item content and properties that
need to be addressed in QOL instruments in the future.
Particularly evidence of validity, reliability, and
responsiveness in opioid-dependent populations was scarce across
tools. The field of QOL measurement in opioid dependence
is in its infancy. This becomes particularly evident when
comparing the results to other instrument reviews. Many
medical disciplines have multiple disease-specific
instruments available for any one condition, and reviews
determine the ‘best’ instrument by assessing psychometric
properties using detailed quality criteria [
]. This would
not have been possible in this review considering the lack
of disease-specific tools and scarce evidence of
psychometric properties. Additionally, instruments in this review
scored rather poorly on the properties. A reason for this
might be that most tools were developed before the year
2000, while numerous guidelines and criteria for the
transparent development and psychometric evaluation of
PRO measures were developed in more recent years
]. We strongly recommend that available guidelines
and criteria be applied in the development of new QOL
Item content relevance of an instrument for a given
study population is important and must be investigated if
the population differs from the one in which the tool was
]. Only IDUQOL was developed for drug
users and no tools specifically for opioid-dependent people.
Accordingly, IDUQOL was the only one of two tools that
comprehensively measured Schalock’s domains. The other
instruments were developed for (and with input from) the
general population or broad mental health populations.
Overall, the instruments varied greatly in their content,
focusing on different life domains. The different foci may
in part be due to the lack of a universally accepted
definition of QOL and because researchers operationalize the
concept differently. Researchers need to be aware of the
different conceptualizations of QOL when selecting an
instrument for a study, as the item content needs to match
the study population. It should be noted that, in the current
literature, self-determination is no longer always seen as a
domain of QOL (as in Schalock’s model) but rather a
prerequisite of QOL. The self-determination theory [
proposes that individuals’ wellbeing is determined by the
fulfillment of three basic needs: autonomy, competence,
and relatedness. This could change how we approach the
concept of QOL in future research.
The field of opioid dependence is in need of a
highquality, disease-specific QOL instrument
9, 22, 23, 41, 42
]. While research consistently shows that
the QOL of opioid-dependent populations is poor, the use
of HRQOL and generic tools may undermine our
understanding of the extent and severity of the impact of the
disease, as well as overestimate the effectiveness of
treatment. The advantage of disease-specific instruments is that
they provide more relevant and sensitive results than
generic instruments, which are applicable across populations
]. Qualitative research revealed that specific barriers in
the domains of social inclusion, rights, and
self-determination reduce the QOL of people with opioid dependence
]. However, it is especially these QOL domains that
were underrepresented in the instruments in this review. In
order to develop a valid and reliable QOL instrument, more
qualitative research will be essential to identify what is
most important to opioid-dependent people for a good
QOL and what needs to be included in an instrument.
Another important observation regarding the literature is
that researchers often did not use the original, validated
instrument but a variation of the tool. Researchers added or
removed items seemingly at random (e.g., SWLS,
MSQOL) or developed a number of different but very
similar versions of an instrument (e.g., LQoLP-modified,
IDUQOL). We speculate that researchers wanted to adapt
the instruments to meet the study needs. However, this
hinders the assessment and comparison of outcomes.
Moreover, sixteen different tools were used in 94 articles.
Increased uniformity of instruments used would enhance
the interpretability of results and the comparability of
outcomes across studies. We also found that about half of
the articles used HRQOL as opposed to QOL instruments,
meaning that measures of HRQOL were still used as much
as nearly a decade ago [
]. While HRQOL instruments are
useful to gain insight on the impact of a disease on patients’
functioning, researchers need to be aware that the term
HRQOL refers to patients’ self-perceived health status and
is not synonymous to QOL [
Limitations to this review relate to assumptions we
made and possible sources of bias. First, we assumed that
Schalock’s domains are key components to a good QOL
for opioid-dependent individuals. Schalock’s model has not
been extensively tested in opioid users yet. Nevertheless
we chose this model because the eight domains have been
found to be pertinent to opioid users, as well as broader
groups of drug users and other marginalized populations
6, 46, 47
]. Second, the coding of instrument items
involved a somewhat subjective evaluation. We tried to
reduce the subjectivity by engaging four independent
coders, developing coding rules, and discussing
disagreements in a consensus meeting. Third, our selection of
instruments may be biased. Five instruments were excluded
from analysis because they could not be retrieved or were
not available in the author’s languages. However, we did
assess the most frequently used tools, which are arguably
more relevant to the literature. Also the frequency of
instrument use may be biased. Foreign language
instruments are more popular in their respective countries and
used more in local journals, which we did not target in our
literature search. Finally, it should be noted that the results
of the content analysis do not indicate opioid dependence
specificity of instruments. This would require an
assessment of content validity. But seeing as the QOL of
opioiddependent people is not precisely defined yet, we took a
more conservative approach and assessed broad QOL
domains that have been shown to be pertinent to opioid
]. A next step might be to assess the content
validity of instruments that performed well in our content
Opioid-dependent people make up the largest proportion
of patients seeking drug treatment and they suffer
wideranging detrimental impacts on their QOL. Yet no
suitable instrument is available to measure QOL in this
population. This review enables researchers to make an
informed decision when selecting a QOL tool, and it
enables improved interpretation of the literature (e.g., by
knowing that certain instruments measure largely
healthrelated aspects of QOL). Furthermore, this systematic
review highlights the pressing need of a multidimensional
QOL instrument that is specific to opioid-dependent
populations. The development of such tool is critical for
advancements in the field. A disease-specific tool will
provide more relevant and valid data and thereby more
accurate assessment of the impact of the disease and
treatment on people’s QOL. Moreover, it will demonstrate
patient needs, providing an incentive for improving
treatment and patient-centered drug policy. We especially
recommend the development of a short QOL questionnaire
that is practical to use in routine patient care, in order to
further bridge the gap between research and practice.
Acknowledgements This work was supported by a research Grant
from the Federal Ministry of Health of Germany (Bundesministerium
fu¨r Gesundheit). The funder had no role in the design or conduct of
Funding This study was funded by the Federal Ministry of Health of
Germany (Grant Number ZMVI5-2515DSM214).
Compliance with ethical standards
Conflict of interest The authors declare that they have no conflict of
Ethical approval This article does not contain any studies with
human participants or animals performed by any of the authors.
Open Access This article is distributed under the terms of the Creative
Commons Attribution 4.0 International License (http://creative
commons.org/licenses/by/4.0/), which permits unrestricted use,
distribution, and reproduction in any medium, provided you give appropriate
credit to the original author(s) and the source, provide a link to the
Creative Commons license, and indicate if changes were made.
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