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Assessing Quality of Life in Older Adults With Cognitive Impairment

From the Department of Psychosocial and Community Health (R.G.L., S.M.M., L.T.), University of Washington School of Nursing, and the Department of Environmental Health (L.E.G.), University of Washington School of Public Health, Seattle, Washington.

Address reprint requests to: Rebecca G. Logsdon, PhD, Box 358733, University of Washington, Seattle, WA 98195-8733. Email: logsdon@ u.washington.edu

	ABSTRACT

TOP ABSTRACT INTRODUCTION Quality of Life and... Methods of Evaluating Quality... Development of the QOL-AD METHODS RESULTS DISCUSSION ACKNOWLEDGMENTS REFERENCES

 
OBJECTIVE: This article discusses theoretical, psychometric, and practical considerations of quality of life assessment in older adults with cognitive impairment. It describes a new measure of quality of life in dementia, the QOL-AD, and examines the reliability and validity of patient and caregiver reports of patient quality of life.

METHODS: Subjects were 177 patient/caregiver dyads. Patient Mini Mental State Exam scores ranged from 0 to 29, with a mean score of 16 (SD = 7). Each patient and caregiver rated the patient’s quality of life on the QOL-AD. Patient functional and cognitive status, psychological state, physical function, and behavior problems were also assessed. Reliability and validity of patient QOL-AD reports were examined across three levels of cognitive impairment.

RESULTS: One hundred, fifty-five patients were able to complete the QOL-AD. Completers scored between 4 and 29 on the Mini Mental State Exam, whereas noncompleters all scored 10 or lower. Reliability for both patient and caregiver reports on the QOL-AD was good ( values ranged from 0.83 to 0.90). Validity of patient and caregiver reports across cognitive levels was supported by correlation with measures of depression (r = -0.41 to -0.65), day-to-day functioning (r = -0.10 to -0.45), and pleasant events frequency (r = 0.18 to 0.51). Intraclass correlation between patient and caregiver reports was positive across all cognitive levels (r = 0.14 to 0.39).

CONCLUSIONS: The QOL-AD seems to be reliable and valid for individuals with MMSE scores greater than 10. Further research is needed to clarify the relationship between patient and caregiver reports of patient quality of life and to identify factors that influence quality of life throughout the progression of dementia.

Key Words: quality of life, • dementia, • Alzheimer’s disease, • caregivers, • patient reports, • proxy reports.

Abbreviations: AD = Alzheimer’s disease;; ADL = activities of daily living;; CESD = Center for Epidemiologic Studies Depression Scale (measure);; GDS = Geriatric Depression Scale;; IADL = instrumental activities of daily living;; ICC = intraclass correlation coefficient;; MMSE = Mini Mental State Exam;; MOS = Medical Outcomes Studies (36-item short form measure);; PES-AD = Pleasant Events Schedule–Alzheimer’s Disease;; QOL = quality of life;; QOL-AD = Quality of Life–Alzheimer’s Disease (measure);; RMBPC = Revised Memory and Behavior Problems Checklist;; SCB = Screen for Caregiver Burden.

	INTRODUCTION

TOP ABSTRACT INTRODUCTION Quality of Life and... Methods of Evaluating Quality... Development of the QOL-AD METHODS RESULTS DISCUSSION ACKNOWLEDGMENTS REFERENCES

 
In the past 10 years, treatments for individuals with Alzheimer’s disease (AD) and related dementias have addressed a variety of goals, including improving cognitive status, delaying the onset of more severe symptoms, maximizing day-to-day functioning, and reducing behavioral problems such as depression and agitation. Despite a variety of approaches, including pharmacological, behavioral, educational, and/or environmental interventions, improvements in patient functioning on standard outcome measures have been modest at best. Important questions have been raised by individuals with dementia, their family members, and professionals who care for them about what outcomes are desirable and meaningful (1–3). This discussion has led to recognition that in addition to specific symptom amelioration, it is important to evaluate the extent to which an intervention improves the quality of life (QOL) of the person being treated.

	Quality of Life and Dementia: Definitions and Challenges

TOP ABSTRACT INTRODUCTION Quality of Life and... Methods of Evaluating Quality... Development of the QOL-AD METHODS RESULTS DISCUSSION ACKNOWLEDGMENTS REFERENCES

 
"Quality of life" is an elusive concept that has been defined and assessed in a variety of ways, depending on the context in which it is used and on the conceptual orientation of the investigator (4). Despite this, as researchers become more aware of the issues involved in assessing QOL, some areas of agreement have emerged. Common threads include the acknowledgment that assessment of QOL involves a subjective global rating by the individual as well as more specific ratings of physical, psychological, and social variables, and the recognition that the exact nature of the assessment of QOL depends on the group being evaluated and the purpose of the evaluation. Lawton (5, 6) has provided a broad conceptual framework for QOL in older adults that includes four domains of importance: behavioral competence, the objective environment, psychological well-being, and perceived QOL. Each of these domains is highly relevant to the assessment of QOL in older adults with cognitive impairment.

Assessing QOL in cognitively impaired older adults poses unique challenges. Although QOL research is well established with other chronic diseases, it has not been widely included in investigations of AD and related dementias.

In 1995, the World Health Organization defined QOL as "the individual’s perceptions of their position in life in the context of the culture and value system in which they live, and in relationship to their goals, expectations, and standards" (7). This definition assumes that individuals have the intellectual capacity to make complex subjective judgments about their lives. Many questions have been raised about the ability of persons with dementia to make such judgments and about the point at which they become unable to do so (8, 9).

Varying deficits of memory, attention, judgment, insight, and communication influence the ability of individuals with cognitive impairment to comprehend questions or communicate their own subjective states. In addition, behavioral or noncognitive symptoms, including depression, agitation, or psychosis, may impact QOL ratings. Finally, judgments about what is important to QOL may change as dementia progresses or as the individual’s living situation changes. What seems very important to QOL in early stages (eg, preservation of intellectual capacity) may seem unimportant in late stages (when safety and comfort may take on primary importance) (2, 10).

Despite these challenges, reasons for measuring QOL in people with cognitive impairment are compelling. QOL assessments provide a format for individuals and their caregivers to express whether an intervention made an important difference in the patient’s life. Such assessments allow researchers to draw conclusions about the extent to which treatments provide intended and "clinically significant" benefits. Furthermore, monitoring changes in QOL in individuals with progressive cognitive impairment may suggest new areas of intervention to maintain or enhance life quality.

	Methods of Evaluating Quality of Life in Dementia

TOP ABSTRACT INTRODUCTION Quality of Life and... Methods of Evaluating Quality... Development of the QOL-AD METHODS RESULTS DISCUSSION ACKNOWLEDGMENTS REFERENCES

 
Various approaches (or combinations of approaches) to the assessment of QOL in patients with dementia are currently under investigation. These include self-reports by the individual with dementia (11–13), proxy reports by a family member or caregiver (9, 14), and direct observation of behaviors assumed to be related to QOL (15, 16). Each of these approaches has strengths and weaknesses.

Self-report directly involves the individual in the assessment, taking into account his or her subjective experiences, and places value on the perspective of the person who has the most to gain or lose from treatment. This respect for the autonomy of the individual is very important from a clinical and ethical standpoint. However, if self-reports are to be useful, it is necessary to design measures that facilitate the individual’s ability to participate despite cognitive impairment and to evaluate the impact of dementia-related problems on the individual’s ability to report QOL. Comprehension of questions and selection of appropriate responses can be facilitated by the use of explicit instructions, face-to-face administration by a trained interviewer, and use of visual cues to remind the respondent of the response options. In addition, a trained interviewer can assess the respondent’s comprehension by asking follow-up questions when the response is unclear or inconsistent.

Proxy reports are usually obtained from a close relative or caregiver of the affected person. They circumvent the cognitive limitations that are problematic for the person with dementia and can be used throughout the course of the disease. However, it must be noted that investigations of both cognitively intact and cognitively impaired individuals have found that proxies consistently rate QOL lower than do the affected individuals themselves (12, 17, 18). Proxy ratings may be influenced by the proxy’s own expectations and belief system, the prior relationship with the person being rated, and current levels of depression or burden (12). When QOL is being used as a basis for decisions about treatment, residential options, or end-of-life choices, it is very important to identify and understand the biases of proxy ratings.

Direct observation of behaviors believed to be associated with QOL has the advantage of being more "objective" in that ratings can be based on predefined behaviors and consistently rated over time. Evaluations of observed affect (15, 19) and pleasant events (20, 21) have been proposed to measure observable attributes of QOL (14). Limitations of this approach include uncertainty about whether what is being observed is what the individual considers to be important to his or her QOL. Direct observations may also be subject to many of the biases associated with proxy ratings. In addition, some raters are very alert and attuned to subtle nuances of affect and behavior; others are not. Thus, training raters in observational strategies is an important component of this evaluation process (15).

	Development of the QOL-AD

TOP ABSTRACT INTRODUCTION Quality of Life and... Methods of Evaluating Quality... Development of the QOL-AD METHODS RESULTS DISCUSSION ACKNOWLEDGMENTS REFERENCES

 
This article presents a psychometric analysis of a new measure, the Quality of Life–Alzheimer’s Disease (QOL-AD) Scale (12), with a large sample of AD patients and caregivers and examines the impact of cognitive impairment on the reliability and validity of the measure. It evaluates the ability of individuals with progressive cognitive impairment to provide a rating of their own QOL and clarifies the point at which they can they no longer reliably do so. It also provides a comparison of patient reports and caregiver reports of patient QOL.

	METHODS

TOP ABSTRACT INTRODUCTION Quality of Life and... Methods of Evaluating Quality... Development of the QOL-AD METHODS RESULTS DISCUSSION ACKNOWLEDGMENTS REFERENCES

 
Subjects
Subjects include 177 AD patient-caregiver pairs who met criteria of the National Institute of Neurological and Communicative Disease and Stroke and the Alzheimer’s Disease and Related Disorders Association for "probable" or "possible" AD based on a comprehensive diagnostic evaluation (22). Subjects were required to be community dwelling, to be ambulatory, and to have an actively involved caregiver who lived with them or spent every day with them. Patients’ mean age was 77.2 years (SD = 7.0), educational level was 13.4 years (SD = 3.3), and mean MMSE score was 16.4 (SD = 7.3). Fifty-six percent were male, and 44% were female; 90% were white, 7% were African American, and 3% were Asian or Pacific Islander. Caregivers’ mean age was 69.6 years (SD = 12.6), and educational level was 13.6 years (SD = 2.5). Sixty-eight percent of caregivers were female, and 32% were male; 80% of caregivers were spouses, 9% were adult children, and 11% were other close relatives or friends who lived with and cared for the patient. Ninety-four percent of patients and caregivers lived together; the remaining 6% did not live together but saw each other every day. Data from the baseline assessment of an ongoing longitudinal study are presented in this investigation.

Measures
Experienced geriatric research interviewers administered all measures in the subjects’ homes. Patients and caregivers completed the interviews and questionnaires independently, in different rooms of the house. Patient measures were administered in interview format; caregivers completed their measures first as questionnaires, and then the interviewer reviewed the questions and clarified any items that were omitted or that caregivers were uncertain how to answer. The entire visit lasted about 1 1/2 hours.

Measures were selected to represent each of Lawton’s conceptual domains of QOL in older adults (6). The domain of "perceived QOL" is assessed by the QOL-AD itself. Other measures were selected to represent "behavioral competence," "psychological status," and "interpersonal environment." In addition, although "physical functioning" was not one of Lawton’s original domains, it was also included in this investigation because of its likely association with QOL in chronically ill older adults.

The QOL-AD (12) is a 13-item questionnaire designed to provide both a patient report and a caregiver report of the patient’s QOL (Appendix 1). To facilitate its use with cognitively impaired individuals, the QOL-AD uses simple and straightforward language, responses are structured in a four-choice format that is consistent across all questions, and all items are rated according to the patient’s current QOL. Specific items for the QOL-AD were selected to reflect Lawton’s four domains of QOL in older adults, and items were reviewed by AD patients and caregivers to ensure content validity as well as by experts in the field of geriatrics and gerontology to maximize construct validity. A prior study of AD patients and caregivers (12) found that the measure had good internal reliability ( = 0.88–0.89) and test-retest reliability over a 1-week interval (intraclass correlations for patient and caregiver reports = 0.76 and 0.92, respectively). Validity was also supported by the correlation of higher scores on the QOL-AD with lower levels of depression, better day-to-day functioning, and higher activity level.

The QOL-AD took an average of 10 minutes to administer to the patient in the interview format. Caregivers were able to complete the questionnaire version of the measure in less than 10 minutes. Up to two missing items were replaced with the mean score of the remaining items, but if more than two items were missing, the entire measure was considered missing. Overall scores were computed separately for the patient and caregiver reports by summing the 13 items, for a total possible score ranging from 13 to 52, with higher scores indicating higher QOL.

The MMSE (23), one of the most widely used screening instruments for cognitive impairment, provides a total score ranging from 0 to 30, with lower scores indicative of greater cognitive impairment. It was administered directly to each patient to obtain an overall level of current cognitive functioning. The MMSE is not identified with any single QOL domain, but measures from each domain may be influenced by cognitive status. Thus in this investigation, the MMSE was used to classify subjects by level of dementia.

Measures of Behavioral Competence
The Physical and Instrumental Self-Maintenance Scale (24) is a 16-item scale that provides a functional assessment of basic activities of daily living (ADLs), such as bathing and dressing, and more complex instrumental activities (IADLs), such as shopping, transportation, and home management. ADL scores range from 6 to 30, and IADL scores range from 8 to 31; higher scores indicate greater impairment. Caregivers completed this measure about the patient.

The Revised Memory and Behavior Problem Checklist (25) (RMBPC) provides an overall assessment of behavior problems as well as an assessment of specific types of problems, including memory, depression, and disruption subscales. It is completed by the caregiver and consists of 24 items that caregivers rate on a scale of 0 (never happened) to 4 (happens daily or more often). Subscale scores are calculated as the mean for items on the subscale, so each has a possible range from 0 to 4, with higher ratings indicative of more frequent problems. The RMBPC has been demonstrated to have good reliability and validity (25). For this investigation the memory and disruption subscales are included in the behavioral competence domain because they provide an assessment of memory-related behavior problems (eg, repeated questions, losing objects) and disruptive behaviors (eg, destroying property, verbal or physical aggression). The depressive subscale is included in the psychological status domain because its focus is on depressive behaviors (eg, crying and tearfulness, talking about feeling lonely).

Measures of Psychological Status
The Geriatric Depression Scale (26) (GDS) is a 30-item, self-report measure that is useful and reliable with older adults in residential care settings (27) and as a caregiver-report measure for AD patients (28). For this investigation, caregivers completed the questionnaire about their patients, and AD patients independently completed the GDS about themselves. Caregivers completed the measure as a questionnaire; patients were interviewed and asked to respond orally to the statements read to them, and their responses were recorded by the interviewer (similar to the procedure used for the QOL-AD). As in the procedure for the QOL-AD, if patients were unable or unwilling to respond to more than 2 of the 30 items, they were considered unable to complete the measure, and the entire measure was scored as "missing." Of the entire sample of 177 subjects, all but 23 were able to complete the GDS. The internal consistency reliability of the GDS in this investigation was good for both patient and caregiver reports ( = 0.83 and 0.87, respectively) and was not adversely affected by patient cognitive status.

The Pleasant Events Schedule–AD–Short Form (20, 21) (PES-AD) asks caregivers to rate whether their patient now enjoys each of 20 activities (yes or no) and how frequently their patient engaged in each activity during the prior month (not at all, 1–6 times, 7 or more times). Scores are computed by adding the frequency for activities rated as enjoyed. Total scores can range from 0 to 40, with higher scores indicating more pleasant activity. In a prior investigation, the PES-AD was demonstrated to have good internal consistency and to correlate with diagnosis and severity of depression in AD patients (20).

Measures of Physical Functioning
Two subscales of the Medical Outcomes Study (MOS) 36-item short form (29) were completed by caregivers about their patients to evaluate patient physical health: the 10-item physical functioning subscale and the 4-item role limitations-physical subscale. These subscales were selected because they have been used in other studies of AD patients and have been found to provide a brief yet reliable and valid assessment of physical health (30). The physical functioning subscale includes items related to mobility and the impact of physical disability on the individual’s ability to walk, climb stairs, lift objects, etc. The role limitations-physical subscale assesses the impact of physical disability on an individual’s ability to carry out usual activities. Total scores on each subscale range from 0 to 100, with higher scores indicating better physical functioning.

Measures of Interpersonal Environment
Because study participants resided at home in the community with a family caregiver, the caregiver’s level of burden and depression were identified as the most salient aspects of the patient’s interpersonal environment. The Screen for Caregiver Burden (31)(SCB) questionnaire was used to assess caregiver burden. The SCB is a 25-item checklist designed specifically for caregivers of AD patients. It provides scores for both objective burden (number of potentially negative experiences) and subjective burden (caregivers’ reported distress in response to these experiences). The SCB has been demonstrated to be reliable, sensitive to change over time, and correlated with both caregiver and care recipient change in the expected directions (31). Scores can range from 0 to 25 for objective burden and from 0 to 75 for subjective burden, with higher scores indicating higher levels of burden.

The Center for Epidemiologic Studies Depression Scale (32, 33)(CESD) was used to evaluate depression in caregivers. This 20-item questionnaire has been found to be reliable and valid with older adults. In an investigation of AD patient and caregiver depression, it was also found to be sensitive to change over time (34). Scores can range from 0 to 60, with higher scores indicative of more depressive symptoms.

Methods of Analysis
Analysis of variance was used to evaluate demographic differences between patients who were and were not able to complete the QOL-AD interviews and to explore cognitive, behavioral, or other factors associated with the ability of patients to complete the measure.

Reliability and validity of the QOL-AD were evaluated for patients who were able to complete the measure and their caregivers. Coefficient was used to assess the internal consistency reliability of patient and caregiver reports on the QOL-AD. Agreement between patient-reported and caregiver-reported QOL-AD ratings was examined for both consistency and absolute agreement, using a two-way mixed model, single-measure intraclass correlation coefficient (ICC).

To evaluate validity, the associations between patient- and caregiver-reported QOL-AD scores and measures representing hypothesized QOL domains were evaluated using Pearson correlation coefficients. It was hypothesized that higher QOL-AD scores would be correlated with less impairment on measures of behavioral competence, better psychological status, better physical function, and better interpersonal environment. Based on prior research, the relative magnitude of correlation was expected to be higher between the QOL-AD and measures of psychological status and lower between the QOL-AD and measures of behavioral competence. The correlation between interpersonal environment and QOL-AD score was expected to be relatively higher with caregiver reports than with patient reports.

To evaluate the impact of cognitive impairment on QOL-AD scores, patients were divided into tertiles according to MMSE scores. This division provided groups that are clinically meaningful in terms of degree of cognitive impairment (low: MMSE 16; middle: MMSE = 17–21; high: MMSE 22) and maximized statistical power for the subgroup analysis. Reliability and validity analyses were repeated for each subgroup to explore the association of the four hypothesized domains with QOL-AD scores at different levels of cognitive functioning.

	RESULTS

TOP ABSTRACT INTRODUCTION Quality of Life and... Methods of Evaluating Quality... Development of the QOL-AD METHODS RESULTS DISCUSSION ACKNOWLEDGMENTS REFERENCES

 
Of 177 patients interviewed, 155 were able to complete the QOL-AD interview; 22 were unable to understand it sufficiently to provide meaningful responses. As shown in Table 1, the primary differences between patients who could complete the QOL-AD and those who could not were associated with cognitive and functional status. Age, education, and duration of dementia were not significantly different between the two groups. Mean MMSE score for patients who were unable to complete the measure was 4.1 (SD = 3.2, range 0–10), compared with 18.1 (SD = 5.9, range 4–29) for those who could complete the measure (F(1,175) = 120.2, p < .001). Both basic and instrumental ADLs were significantly more impaired among patients who could not complete the QOL-AD than for those who could complete the interview (F(1,175) = 58.11, p < .001 and F(1,175) = 34.44, p < .001, respectively). Caregiver reports of QOL-AD scores and GDS scores were not significantly different between the two groups, but caregivers of patients who could not complete the QOL-AD reported more disruptive behaviors (F(1,175) = 4.02, p < .05), worse physical functioning (F(1,175) = 4.35, p < .05), and fewer pleasant events (F(1,175) = 4.50, p < .05). Caregivers of these subjects also reported significantly higher levels of objective burden (F(1,174) = 8.82, p < .01) but did not report greater feelings of subjective burden. Neither patient nor caregiver depression was significantly different between the two groups.

MMSE scores were not significantly correlated with either patient- or caregiver-reported QOL-AD scores (r = 0.12 and 0.02, respectively). Validity was assessed with Pearson correlation coefficients between the QOL-AD and measures of the four hypothesized domains of QOL. As shown in Table 2, most correlations were significant in the hypothesized directions, with higher QOL related to less impairment in behavioral competence, better psychological status, less impaired physical function, and a better interpersonal environment.

All measures from the psychological status domain were significantly correlated with QOL-AD scores in the hypothesized directions; the strongest associations were between both patient- and caregiver-reported QOL-AD ratings and the GDS scores (r = - 0.51 and -0.52 respectively; p < .001). The RMBPC depression subscale was significantly correlated with both patient- and caregiver-reported QOL-AD ratings (r = -0.22 and -0.23 respectively; p < .01), and higher frequency of pleasant events was associated with higher patient- and caregiver-reported QOL-AD ratings (r = 0.30 and 0.44 respectively; p < .001).

One of the physical functioning domain measures, the MOS physical function, was correlated with both patient- and caregiver-reported QOL-AD ratings (r = 0.22 and 0.43, p < .01 and p < .001, respectively). MOS role limitations-physical was correlated with caregiver-reported QOL-AD ratings (r = 0.20, p < .01) but not with patient-reported QOL-AD ratings (r = 0.11, NS).

In the interpersonal environment domain, caregiver burden was significantly correlated with both patient- and caregiver-reported QOL-AD ratings but was more strongly associated with the caregiver-reported QOL-AD (objective burden: r = - 0.52; subjective burden: r = -0.53; p < .001) than with the patient- reported QOL-AD (objective burden: r = -0.21; subjective burden: r = -0.19; p < .01). Caregiver depression was significantly correlated with caregiver-reported QOL-AD (r = -0.48, p < .001) but not with patient-reported QOL-AD (r = -0.12, NS).

To evaluate the reliability and validity of patient and caregiver reports at different levels of cognitive function, individuals who completed the patient report (N = 155) were divided into tertiles according to MMSE scores. As shown in Table 3, educational level was significantly different among the groups (F(2,151) = 5.3, p < .01). However, education was not significantly related to either patient or caregiver QOL-AD ratings; thus it did not confound the associations of other factors with the QOL-AD. As expected, the groups differed significantly on ADL (F(2,152) = 12.3, p < .001), IADL (F(2,152) = 21.2, p < .001), and duration of dementia (F(2,149) = 5.3, p < .01). The groups also differed on the MOS role limitations subscale (F(2,152) = 3.4, p < .05) and caregiver objective burden (F(2,152) = 4.0, p < .05). Patient-reported QOL-AD ratings were significantly different, with lower QOL reported among the lowest cognitive group (F(2,152) = 3.3, p < .05), but caregiver-reported QOL-AD ratings did not differ across groups. No significant differences were found on age, physical function, depression, disruptive behaviors, or frequency of pleasant events.

In the physical functioning domain, MOS physical function was significantly correlated with QOL-AD for all groups on the caregiver reports and for the middle cognitive group on the patient reports. The MOS role limitations physical was not significantly correlated with the QOL-AD, except in the patient-report middle cognitive group.

In the interpersonal environment domain, caregiver burden was significantly correlated with caregiver-reported QOL-AD at all levels of patient cognitive functioning but was significantly correlated with patient-reported QOL-AD only at the middle cognitive level. Similarly, caregiver depression was significantly correlated with caregiver-reported QOL-AD at all levels of patient cognitive functioning; it was not correlated with patient-reported QOL-AD at any cognitive level.

	DISCUSSION

TOP ABSTRACT INTRODUCTION Quality of Life and... Methods of Evaluating Quality... Development of the QOL-AD METHODS RESULTS DISCUSSION ACKNOWLEDGMENTS REFERENCES

 
This investigation demonstrates that it is possible for individuals with mild to moderate dementia to reliably and validly rate their own QOL. In this sample of 177 subjects with MMSE scores ranging from 0 to 29, all but 22 subjects were able to respond to the QOL-AD interview questions. Of those who completed the interview, MMSE scores ranged from 4 to 29, and no subject who scored 11 or higher on the MMSE was unable or refused to complete the QOL-AD.

There was no difference in caregiver ratings of QOL for subjects who could and could not complete the QOL-AD. This finding is somewhat surprising, because subjects who could not complete the QOL-AD were more cognitively, functionally, and behaviorally impaired. However, depressive symptoms, which are strongly associated with QOL, were comparable in subjects who could and could not complete the QOL-AD. It seems likely that when caregivers formulate their QOL ratings, they take into account a variety of factors and that their observation of the patient’s mood is a critical component in their QOL rating.

For the 155 patients who completed the interview, coefficient scores for both patient reports and caregiver reports indicated good internal consistency. The validity of the patient-reported QOL-AD is supported by expected correlations with at least one measure from each hypothesized domain: the ADL scale from the behavioral competence domain, all measures from the psychological status domain, the MOS physical function scale from the physical functioning domain, and both objective and subjective burden from the interpersonal environment domain. The validity of the caregiver report is supported by correlations with every measure representing each of the four domains.

When subjects were divided into tertiles by cognitive level, psychological status, as measured by the GDS, remained prominent in its relationship to both patient- and caregiver-reported QOL at all levels of cognitive functioning. Thus, it seems that regardless of cognitive status, depression has a strong impact on QOL. In other domains, considerable variability was found in correlations between QOL-AD scores and related measures. Differences in frequency distributions of the measures across cognitive levels are a possible explanation for these findings. However, there was no evidence of "floor" or "ceiling" effects, and the variance of each measure was relatively similar across groups. Sample sizes were relatively small for the subgroups; with larger samples, more significant correlations would likely be identified.

Another explanation for differences among cognitive groups is that factors that influence QOL may differ for both patients and caregivers at different stages of patient cognitive impairment. For example, early in the disease process, caregivers may be more attuned to changes in IADLs; in the middle stages, behavioral disturbances are more significant; and in later stages, ADL changes are most important. Patients in the early stages of AD may be unaware of their memory and IADL impairment or may deny such impairment, but as the disease progresses and they require more assistance with basic ADLs, their awareness of their deficits may increase. Thus, ADL impairment may have a greater impact than IADL impairment on patients’ perceptions of their own QOL. Similarly, decreased physical functioning is associated with later stages of AD and may play a more prominent role in QOL assessments as the disease progresses. Another reason for differences across cognitive levels is that behaviors and skills that are actively declining may influence perceptions of QOL. During times of change, these factors may be associated with QOL ratings, but once the change has occurred and the individual and caregiver have adjusted to it, those factors may no longer be as important to QOL. These questions can best be answered in longitudinal investigations, in which individuals are evaluated repeatedly over the progression of their dementia.

In this investigation, the level of agreement between patient and caregiver ratings of QOL was modest. The correlation between caregiver and patient reports was greatest for subjects in the middle tertile of cognitive function, but cognitive ability did not seem to be the most salient explanatory factor because the correlations of both the lowest and highest cognitive groups were similar. In addition, a prior investigation found that test-retest reliability was good for both patient and caregiver reports and was not affected by cognitive status for subjects with MMSE scores greater than 10 (12). Because there is no "gold standard" for QOL and it is widely agreed that QOL assessment involves subjective perceptions, the correlation between patient and caregiver reports likely reflects a real difference in the way they perceive the patient’s QOL rather than a lack of reliability of the measure itself.

Caregiver reports were strongly correlated with both caregiver depression and burden, whereas patient reports were less influenced by caregiver burden and were, for the most part, not significantly related to caregiver depression. One explanation for differences between patient and caregiver reports of QOL (in which caregivers consistently rate QOL lower than patients) is that caregivers’ ratings are influenced by their own experiences and psychological status. Caregivers who are highly burdened or depressed may rate their patient’s QOL lower because they have a negative bias that influences their perspective. It is likely that a variety of factors contribute to the differences in QOL ratings and that these differences are not unique to QOL assessment in cognitively impaired individuals. Prior investigations with cognitively intact individuals have demonstrated that family members tend to rate depression higher and functional status lower than the person being rated (17, 18). This finding was replicated in this investigation of AD patients and family caregivers. Additional evaluation of potential sources of bias in both patient and caregiver reports is needed.

In summary, the assessment of QOL in patients with cognitive impairment is an important and fruitful area for future investigation. It has been assumed in the past that patients with dementia would not be able to rate their own QOL because of the nature of their disease. This investigation indicates that that is not the case and that individuals can rate their own life quality well into the progression of the disease. Furthermore, this investigation suggests that caregiver ratings do not substitute for patient ratings. Future research should address factors that affect both patient and caregiver ratings and identify strategies to improve the accuracy and reliability of evaluations of QOL and other subjective states in cognitively impaired older adults.

	ACKNOWLEDGMENTS

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This research was supported by grants from the National Institute on Aging (AG-13757, AG-10845, and AG-05136), and from the Alzheimer’s Association (FSA-95-009). We gratefully acknowledge the contributions of Amy Moore, MS, who serves as project manager; Kari Mae Hickman, MSW, and Julie Cleveland, BA, who interviewed subjects; and the participants and caregivers who participate in the ongoing study.

Received for publication July 25, 2000.

	REFERENCES

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