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Quality of life utility scores

do they correlate with self-rated quality of life in people with MS?

Karen VL Turpin, Sharon A Warren, Kenneth G Warren
University of Alberta, Canada.

Way Ahead 2010;14(1):10-11

Measurement of a condition as variable as MS is notoriously difficult to achieve, but evidence based decisions support the development of suitable measures. For a measure to be meaningful it must be reliable, reproducible and valid. At face value, many commonly used clinical measures are deemed to be reliable, reproducible and valid measures of the impact of MS on various aspects of an individual's functional activities and quality of life. However, further consideration needs to be given to whether the aspects of life considered important to the person with MS are the same as those which society/clinicians consider important.

In the following article, Karen Turpin examines the discrepancies between the results of two generic health profile measures; one a utility measure based upon five predefined areas of health, and the other a patient-rated quality of life measure; from which a number of interesting conclusions may be drawn.

Introduction

The term quality of life (QoL) is used to describe a subjective sense of wellbeing or global satisfaction with important aspects of daily life. Quality of life is generally measured using one of two approaches; specific instruments or generic instruments.

Specific instruments

Specific instruments measure those aspects of life whose quality is most likely to be affected by a specific disease. An example of a specific instrument that is used in MS is the Multiple Sclerosis Impact Scale (MSIS-29). The MSIS-29 measures 20 physical and 9 psychological items assessing how much impact they have on life from the patient's perspective. This combines both quality of life issues and psychometric testing.

Generic instruments

Generic health profile instruments measure all aspects of quality of life that might be affected by health and can therefore be used in any disease or the general population. An example of a generic instrument that may be used for people with MS is the Medical Outcome Study Short Form 36 Health Survey (SF36). The SF36 measures the health status in eight dimensions including physical function, pain, general health, vitality, and social functioning.

Generic utility measures represent quality of life in single numbers along a continuum that usually extends from 0.0 (death) to 1.0 (full health). Utility measures are frequently used in clinical trials and cost-benefit analyses and are useful for determining if individuals are overall, better or worse off than others.

However, the scoring algorithms for utility measures are based on values society or clinicians have placed on health rather than by the people who actually live with the conditions being measured. Clinicians and researchers are thus beginning to question the appropriateness of reporting MS patients' quality of life measures based on societal values when patient self-valuation measures appear to offer a much more sensitive means of capturing such information.

The present study had two objectives:

To determine if differences exist between self-rated quality of life scores and utility measure quality of life scores.
To delineate possible explanatory factors for any discrepancy between the two types of quality of life evaluations.

Methods

Participants for this study were recruited from the Northern Alberta MS Patient Care and Research Clinic at the University of Alberta in Edmonton, Alberta, Canada, the major MS referral centre for north-central Alberta. This study was conducted as part of a larger study designed to assess the quality of life of people living in a variety of care situations. All people on the clinic's patient register who were known to live in assisted living or long-term care facilities were invited to participate, along with a random sample of patients living at home independently or with home care.

89 people responded, producing a sample which included: 45 people living within their own home independently; 10 people living within their own home with home care; 9 people living within an assisted living facility; and 25 people living within a long-term care facility. A self-report mail survey was used to collect the data. Return of the anonymous questionnaire implied consent.

The participants were asked to complete two quality of life evaluations: the European Quality of Life-5 Dimension questionnaire (EQ-5D) a standard generic utility instrument developed for describing and valuing health states; and a self-report questionnaire, the European Quality of Life Visual Analog Scale (EQ-VAS) that generates a self-rated quality of life measure based on the individual's own values and experiences of MS.

The EQ-5D weights a person's health status by the quality of life that society/clinicians associate with specific levels of health. It is a standardised instrument, which has been used in a wide range of health conditions and treatments and provides a single index value for health status. It is designed for self-completion and is ideally suited for use in mail surveys.

The five pre-defined dimensions of the EQ-5D are:

mobility
self-care
usual activities
pain/discomfort
anxiety/depression

For each dimension, respondents are asked to choose from 1 of 3 descriptors that best describe their current state of health. The responses to these five dimensions are then combined to create one single overall EQ-5D score (0.0 = worst QoL to 1.0 = best QoL). The EQ-VAS asks participants to indicate how good or bad they think their health is on a scale of 0 to 100, with 0 being the worst state they can imagine and 100 the best.

The difference between the scores emerging out of the EQ-5D and the EQ-VAS was calculated for each participant.

Results

In general, the participants in the independent living group were more likely to be younger, married, working, receiving a higher income, and experiencing a relapsing remitting course of MS and lower disability level than the participants in the other three groups.

The average EQ-VAS and EQ-5D scores, along with the calculated mean difference between the scores for each group, are presented in Table 1.

When the questionnaires were analysed it emerged that the independent living group scored significantly higher on the EQVAS than the long-term care group, and scored significantly higher on the EQ-5D than all three of the other groups. In spite of this, the independent living group showed the biggest discrepancy between their EQ-VAS and EQ-5D scores than the assisted living and long-term care groups.

With the exception of the independent living group, all groups scored higher on the EQ-VAS scale than on the EQ-5D scale. A statistically significant mean difference of 7.20 was found between the EQ-VAS (58.7) and the EQ-5D (51.5) scores when the difference between scores across the group as a whole were calculated.

Linear regression analyses were performed to determine those factors that may explain the difference between patients' own self-valuations of their quality of life and the results produced by a utility measure for quality of life.

The initial univariate analyses found patients with higher EQ-VAS scores than their EQ-5D scores (positive differences) tended to:

be older
no longer employed
experiencing a more progressive course of MS
have a higher disability level
have a longer disease duration
be living in a long-term care setting

When these six factors were entered into a multiple linear regression analysis, living in a long-term care setting was the largest and most significant predictor of having a self-evaluation of quality of life EQ-VAS score that was much higher than their EQ-5D score. Longer disease duration was the next significant predictor. Together these two factors - living in a long-term care setting and longer disease duration - accounted for 47.4% of the variance in the dependent variable.

Table 1 EQ-VAS and EQ-5D quality of life scores

Mean scores	Independent living (n=45)	Home care (n=10)	Assisted living (n=9)	Long-term care (n=25)
VAS	64.8	52.2	57.8	50.8*
EQ5D (x100)	71.9	45.5†	35.7‡	22.2‡
Difference (1-2)	-7.1	+6.7	+22.1†	+28.6‡

*Significant difference with the independent living group, p≤=.05
†Significant difference with the independent living group, p≤.01
‡Significant difference with the independent living group, p≤.001

Discussion

The independent living group produced a higher EQ-5D scores than EQ-VAS scores whereas the long-term care group produced higher EQ-VAS scores than EQ-5D scores. Based on these findings, it seems plausible that progression from independent living to long-term care may result in a parallel evolution in self-valuations of quality of life. Psychological adjustment to the disease and/or a shift in priorities may be occurring as people with MS make the transition from independent living into long-term care. These psychological phenomena could explain the discrepancies that exist between EQ-5D and EQ-VAS scores.

Furthermore, the study suggests there are variables that influence how people with MS rate their own quality of life - factors such as duration of disease and residential status - that are not captured in single score utility instruments such as the EQ-5D.

Conclusion

Quality of life utility instruments were designed for cost-benefit analyses and other health economic focused studies, and as such, make useful tools in health policy decision-making. Although they can also be used in clinical trials, these instruments may not be appropriate when the impact of a condition or a treatment on the quality of life of patients from their personal and/or collective perspective is sought.

Furthermore, the quality of life scores obtained from utility instruments may be misleading, especially for those persons with MS who reside in long-term care facilities or have lived with the disease for a long period of time.