Introduction
Human immunodeficiency virus (HIV) and acquired immune deficiency
syndrome (AIDS) entered the public consciousness over two decades
ago. In the ensuing years, interest in the measurement of self-reported
functioning and well being, or health-related quality of life (HRQOL), in
HIV-infected individuals has been extensive [
1‐
4]. While the treatment
for HIV-infection remains non-curative, the improvements in mortality
and AIDS-free survival for HIV-infected individuals have been substantial [
5,
6].
The modification of the natural history of the disease with multi-pharmaceutical
regimens that have diverse beneficial as well as toxic effects [
7] makes
the measurement of HRQOL in this patient population more important
than ever. However, there is no consensus regarding the best measurement
approach.
When a particular disease is being considered, there is a tendency
to assume that disease-targeted measures are superior to general
or generic measures. HIV/AIDS is no exception. Numerous HIV/AIDS-targeted
HRQOL measures have been developed. A recent review [
8] evaluated the
psychometric properties of HIV disease-targeted HRQOL instruments.
Based on their review, the authors could not recommend the use of
any of the instruments reviewed; however, the MOS-HIV was found
to have the most available evidence for the evaluation criteria applied.
Regardless of the lack of compelling arguments for its use, the
MOS-HIV appears to be the most popular HRQOL instrument currently
reported in the HIV literature. The purpose of this investigation
is to examine the use of the MOS-HIV, a measure targeted at HIV
disease, with the leading generic HRQOL instrument, the SF-36, in studies
of persons with HIV.
The Medical Outcomes Study
The Medical Outcomes Study (MOS) was a four-year observational
study that investigated the changes in physician practice styles
and patient outcomes under different healthcare settings such as
health maintenance organizations, large physician groups, or individual
physician fee-for-service practices [
9].
One of the goals of this longitudinal study was to construct reliable
and valid tools for measuring and monitoring patient-reported functioning and
well-being [
10]. To complement
the conventional clinical outcomes in the study, a spectrum of patient-reported
outcome measures was created [
11].
The MOS Short Form 20-Item Health Survey (SF-20), a brief, generic
health status instrument that provides six scale scores (general
health perceptions, physical function, role function, social function,
pain, and mental health), was the first short form developed from
the MOS and was used for the screening of patients for chronic disease
status during the cross sectional phase of the study [
11]. The SF-36, a second generation of
the short form, includes an additional health concept (energy/fatigue), increases
the precision of previous single-item measures (pain, social functioning)
and multi-item measures (physical functioning) by adding additional
items, measures the extent of physical limitations rather than the duration
of the limitation, and focuses on a wider array of role limitations.
The SF-36 was developed for the longitudinal phase of the MOS. At
least nine short form instruments developed from the MOS scales
have been used in studies of HIV-infected persons [
11]. Among those instruments, the MOS-HIV
has been reported to be the most widely used by researchers in patients
with HIV infection [
2,
12,
13].
Background to MOS-HIV and SF-36 Instruments
Owing to the perceived need for a succinct instrument to evaluate
HRQOL in HIV-infected patients in multi-center AIDS clinical trials,
the development of the MOS-HIV was begun in 1987 [
14]. Sixteen items selected from the six scales
of the SF-20 were the foundation for the construction of MOS-HIV.
Four additional scales that were hypothesized to be related to the
health status of HIV-infected persons (i.e., cognitive functioning
[4 items], energy/fatigue [4 items], health distress [4 items] and quality
of life [1 item]) as well as a single item assessing health transition
were added to the original scales in the SF-20, resulting in a 30-item
questionnaire [
14]. The original
MOS-HIV included only one general health perception item. Subsequently,
the 4 other SF-20 current health items were added, leading to the
34-item MOS-HIV. With the addition of a second pain item, the current
version of the MOS-HIV (distributed by the Medical Outcomes Trust)
contains 35 items. It covers 11 dimensions of health including physical
functioning, role functioning, pain, social functioning, emotional
well-being, energy/fatigue, cognitive functioning, general health,
health distress, overall QOL, and health transition. Mental (MHS) and
physical health summary (PHS) scores can be calculated from the
MOS-HIV scales [
15]. The MOS-HIV scales range
from 0 to 100, with higher scores representing better functioning
and well-being. The MHS and PHS are scored using a method that transforms
the scores to a standardized scale (T score) with a mean of 50 and
a standard deviation of 10 in the sample in which the summary scores
were developed [
15]. Mean PHS and
MHS scores above or below 50 can be interpreted as having better
or worse HRQOL than the HIV-infected patient sample from which the
summary measures were developed.
The SF-36 is one of the most widely used HRQOL instruments [
16] and has demonstrated high levels of
reliability and validity in diverse patient populations [
17,
18].
It has 36 items that measure eight multi-item health concepts (i.e.,
physical functioning, role-physical, bodily pain, general health,
vitality, social functioning, role emotional, and mental health).
This instrument was developed to address the health-related concepts
that are most influenced by disease states and their related treatments [
11]. The SF-36 can be scored to yield
two orthogonal factor-based component summary scores for mental
and physical health. The mental (MCS-36) and physical component summary
(PCS-36) scores were derived from the eight scales of the SF-36
using principal components analysis of the total patient sample
from the MOS and a sample of the general US population [
19]. These physical and mental components
account for 82% of the reliable variance in the SF-36's scales in
the general US population. The SF-36 scales are scored on a 0 to
100 possible range, with higher scores representing better functioning
and well-being. The MCS-36 and PCS-36 are scored using a method that
transforms the scores to a standardized scale (T-scores) with a
norm of 50 and a standard deviation of 10 in the general US population.
Sample mean MCS-36 and PCS-36 scores above or below 50 can be interpreted
as having better or worse HRQOL than the general US population.
With norms established in subgroups based on gender and age and
thirty medical conditions, including "healthy" with no chronic conditions,
this standardized scoring provides a means of comparing results
across patients with diverse medical conditions [
20].
Examples of Studies of Persons with HIV using MOS-HIV
or SF-36
A series of literature searches was performed to identify studies
that measured health status in persons with HIV with the SF-36 or
MOS-HIV. The literature in three databases, Medline, HealthStar,
and PsychInfo, was searched from 1975 through 2002. The terms "quality
of life," "HIV," and the name of the MOS instrument (i.e., SF-36 or
MOS-HIV) were cross-referenced in each search of the databases.
Only articles written in English were included.
Discussion
Although other MOS-derived instruments have been used, studies
incorporating either the MOS-HIV or SF-36 were found to be the most
prevalent in studies of HIV disease. Thirty-nine citations for the
MOS-HIV were found which presented empirical data [
12,
15,
21‐
57].
Fourteen empirical articles were found for the SF-36 [
20,
58‐
70]. At the time of
this review, more than 40 cross-cultural translations were available
for the SF-36 and 14 translations for the MOS-HIV [
14,
71].
Only the SF-36 and the SF-12 (a subset of items from the SF-36 that
reproduces > 90% of the variance of the SF-36's summary scores) [
19] have norms available for their summary/composite
measures that have been calculated from nationally representative samples.
Table
1 compares the numbers
of items for each of the scales of the MOS-HIV and SF-36. The SF-36
has four additional items for the measurement of the physical functioning
domain (10
vs. 6), five more items for the role functioning
domains (7
vs. 2), and one more item for the social functioning
domain (2
vs. 1) than the MOS-HIV. However, the MOS-HIV
measures three domains (two with multi-item scales [cognitive functioning
and health distress] and one with a single item [overall quality
of life]) that are not measured by the SF-36.
Table 1
Number of items
in the scales of the MOS-HIV and SF-36.
Physical functioning | 6 | 10 |
Role functioning | 2 | 7 |
Pain | 2 | 2 |
Social functioning | 1 | 2 |
Emotional well-being | 5 | 5 |
Energy / fatigue | 4 | 4 |
Cognitive functioning | 4 | 0 |
General health | 5 | 5 |
Health distress | 4 | 0 |
Overall QoL | 1 | 0 |
Health transition | 1 | 1 |
The two instruments take about five to ten minutes to be self-administered
and can be interviewer administered in person or by telephone [
48]. Reliability has been supported for
the MOS-HIV [
14,
15]and the SF-36 [
20,
59,
72]. in this patient
population. Support for item discrimination of the MOS-HIV has been
shown in comparison with other HIV-targeted and generic HRQOL instruments [
14]. One study found no differences in
health distress and quality of life scale scores of the MOS-HIV
in patients with early
vs. late stages of HIV disease [
12]. Differences have been found between
HIV-infected and non-infected persons on all scales of the SF-36 [
66] while only the summary scores of MOS-HIV
distinguished between these two groups [
22,
23].
The physical health summary scores from the SF-12 and the MOS-HIV
both have been found to discriminate between HIV-infected patients
with <200
vs. ≥ 200 CD4 t-cell counts [
32,
73].
The summary scores of the SF-36 have been shown to be responsive
to HIV disease progression [
20,
74].
The MOS-HIV has been useful in illustrating changes in clinical
status between treatment and control groups in intervention and
observational studies; however, the role functioning, pain, mental
health, health distress, and quality of life scales were shown to
be non-responsive to treatment in one anti-retroviral intervention
study [
29]. Ceiling effects have
been found for the physical functioning, role functioning and role
emotional scales of the SF-36 [
60] and MOS-HIV [
37,
55].
Ceiling effects have been found in the cognitive functioning, pain,
and health transition scales of the MOS-HIV in HIV-infected patients
with more advanced HIV disease [
35].
In addition, the role functioning scale of the MOS-HIV has been
found to have floor effects in HIV-infected patients with more advanced
HIV disease [
21,
22,
35,
37].
Conclusions
One of the primary distinctions between the MOS-HIV and the SF-36
is the availability of nationally representative norms for the SF-36.
Mental and physical health summary scores can be calculated for
the MOS-HIV, but norms for these scores are available from only
the subjects in the studies from which they were developed. The
availability of nationally representative normative data permits
the comparison of summary scores from one individual or a group
of study subjects with scores from a sample representative of the
general population. In addition, nationally representative norms
for the MCS-36 and PCS-36 summary scores are available for males
and females in seven age groups and for fourteen chronic conditions [
75]. These norms permit healthcare decision makers
to utilize the summary scores from the SF-36 to compare the health
status of HIV-infected persons with other persons of similar gender
and age, or with another chronic condition.
Perceived health of asymptomatic HIV-infected individuals does
not appear to vary much from non-infected subjects. Wu and colleagues [
76] demonstrated that HRQOL in HIV-infected
patients with no symptoms or significant abnormalities was not different
from that of healthy non-infected individuals. In a more recent
study, Hays and colleagues found that the physical functioning of
asymptomatic HIV-infected subjects was similar to that of the general
US population [
74]. In addition to
increased measurement precision, using the SF-36 in patients in
the early stages of HIV disease would allow a researcher to compare
and contrast the health status of these HIV-infected individuals
with the health status of patients with diverse chronic conditions
in a range of cultures.
While the MOS-HIV has demonstrated evidence of reliability, construct
validity and responsiveness among HIV-infected patient subjects, [
12,
15,
42,
43,
77] there are limitations
to the instrument. To allow for the addition of "disease-targeted"
scales while not increasing respondent burden, the developers of
the MOS-HIV sacrificed some measurement precision for the physical
functioning, social functioning, and role functioning scales by
reducing the number of items [
21,
24,
35,
37].
These scales, in particular, appear to be important in assessing
HRQOL in this patient population since the majority of the persons infected
with HIV are young adults who are still functioning normally in
society and may not perceive themselves as having functional impairment [
13,
37].
For example, the full-length 10-item physical functioning scale
of the SF-36 allows for the sampling of a wider range of severe and
minor physical limitations and may provide for a better representation
of the levels and types of physical limitations in this population [
18]. The decreased measurement precision
of the functioning scales in the MOS-HIV may explain why ceiling
and floor effects have been found in a number of studies. Ceiling
and floor effects become problematic when patients in longitudinal studies
score the lowest or highest possible score at the baseline since
subjects then can not report any lower or higher score that may
occur if their health status deteriorates or improves at follow-up
[
78].
The MOS-HIV was developed over a decade ago when HIV disease
and its treatment were very different from today [
79]. At that time, rapid health deterioration
from HIV disease and its associated sequelae was prevalent. With rapid
progression into the late stages of HIV disease, monitoring the
HRQOL of patients who were developing HIV-infection associated sequelae
such as cancers (e.g., Kaposi's sarcoma), opportunistic infections
(e.g., pneumocystis carinii pneumonia), and AIDS dementia was imperative.
The disease-targeted scales (i.e., cognitive functioning, health
distress, and quality of life) added to the 16 items from the SF-20
to develop the MOS-HIV were included in the instrument to measure
domains hypothesized to be associated with the HIV disease-related
health deterioration [
12]. Currently, however,
with the availability of HAART, HIV disease is, for the majority
of patients, a chronic rather than acute condition [
79] and, as such, may require an instrument
to assess HRQOL that was designed for chronic rather than acute
diseases. Indeed, empirical evidence supporting the construct validity
of the disease-targeted scales of the MOS-HIV is limited [
12].
The current chronic nature of the disease may preclude the necessity
to monitor the HIV disease-targeted domains of the MOS-HIV in the
general population of HIV-infected patients. Nevertheless, if monitoring
of HIV disease-targeted health concepts is important, the MCS-36
summary score of the SF-36 is strongly correlated with the cognitive functioning
(r = 0.70) and quality of life (r = 0.68) scales and negatively
correlated with the health distress (r = -0.57) scale of the MOS-HIV [
75]. This indicates that the MCS-36 represents
these health concepts to some degree. Furthermore, in populations
of patients in the late stages of HIV disease, augmenting the SF-36
with additional scales or instruments targeting the specific consequences of
the disease and its treatment may be an effective approach. Two
abstracts presented at the 1996 International Conference on AIDS
found that the addition of HIV disease-targeted scales to the SF-36
did not detract from the measurement precision of the SF-36-specific
scales or increase response burden appreciably and did provide for the
effective monitoring of HIV disease [
80,
81].
Our results were based on studies identified through several
databases. There are other databases that may have contained studies
that were not included in our evaluation. In addition, there were
only 14 studies identified that utilized the SF-36 in HIV-infected
persons. It is possible that additional studies are needed to more
fully document the strengths and shortcomings of this instrument. In
sum, this study revealed that although the MOS-HIV has been used
widely in the monitoring of HIV-infected persons, it has noteworthy
limitations that may constrain its applications in this population.
Hence, there is insufficient evidence in the literature to support
the use of the MOS-HIV rather than the SF-36 in HIV-infected persons. Although
the SF-36 is not targeted at HIV, it may be preferable to use the
SF-36 over the MOS-HIV due to fewer ceiling effects, availability
of national norms, and the vast amount of data for other populations
in the U.S. and around the world. Head-to-head comparisons demonstrating
the unique value of the MOS-HIV over the SF-36 are clearly needed.
In addition, more work needs to be directed at comparing the MOS-HIV
and other putatively HIV-targeted instruments to one another to
help demarcate aspects of HRQOL that are truly generic versus specific
to HIV disease.
Acknowledgements
Ron D. Hays, Ph.D., was supported in part by the UCLA/DREW Project EXPORT,
National Institutes of Health, National Center on Minority Health
& Health Disparities, (P20-MD00148-01) and the UCLA Center for Health
Improvement in Minority Elders / Resource Centers for Minority Aging
Research, National Institutes of Health, National Institute of Aging, (AG-02-004).
Authors' contributions
JS reviewed the literature and drafted the manuscript. TD helped
with the literature review and drafting of the manuscript. RDH provided
feedback about the initial idea and editorial input to the drafts
of the manuscript. SJC oversaw the effort and was involved in drafting
and revising the manuscript from start to finish.