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American Journal of Alzheimer's Disease and Other Dementias logoLink to American Journal of Alzheimer's Disease and Other Dementias
. 2012 Aug 16;27(7):474–482. doi: 10.1177/1533317512456449

A New Measure of Caregiver Burden in Alzheimer’s Disease

The Caregiver-Perceived Burden Questionnaire

M Haim Erder 1,✉, Teresa K Wilcox 2, Wen-Hung Chen 2, Sean O’Quinn 3, Juliana Setyawan 1, Judith Saxton 4
PMCID: PMC10697400  PMID: 22904030

Abstract

Objective:

To validate the Caregiver-Perceived Burden Questionnaire (CPBQ) and report its psychometric properties.

Methods:

The CPBQ was administered to caregivers of patients with moderate-to-severe AD in a double-blind randomized trial comparing extended-release memantine to placebo (n = 676). Measurement properties were analyzed using factor analysis, classical test theory, and Rasch analysis.

Results:

Two subscales were identified: the Caregivers’ Assessment of the Patient (CAP) and the Caregivers’ Assessment of Themselves (CAT). The reliability was .89 (CAP) and .83 (CAT). The CAP scores were significantly correlated (r > .3) with scores from the Severe Impairment Battery (SIB) and the Neuropsychiatric Inventory (NPI). The CAT scores were significantly correlated with NPI scores. The CAT discriminated among patients by clinician-rated severity and significantly differentiated between responders and nonresponders.

Conclusion:

The CPBQ appears to be a reliable, valid, and responsive measure that enables linking caregiver’s perceptions about burden and patient function in patients with moderate-to-severe AD.

Keywords: Alzheimer’s disease, caregiver burden, caregiver-perceived burden questionnaire, patient-reported outcomes (PROs), caregiver-reported outcomes (CROs), PRO instrument development, PRO instrument validation

Introduction

Alzheimer’s disease (AD) is a common form of dementia characterized by progressive deterioration of cognitive abilities and memory, resulting in executive dysfunction, behavioral disturbances, and impairment in the patient’s ability to communicate and complete activities of daily living (ADLs). 1,2 The progressive deterioration of patient functioning and abilities often necessitates increasing reliance on others for care. With a growing emphasis on ambulatory rather than institutional care, the burden of caring for people with AD often falls upon the patient’s family members who serve as informal caregivers. 3 -5 Caregiver perceptions of substantial burden have been associated with a number of deleterious caregiver outcomes including poor mental and physical health, lower self-reported quality of life, and increased financial strain. 3,4,6 -12 Moreover, patients with overburdened caregivers may be at increased risk for many of the same poor outcomes and nursing home placement. 3,13,14

The degree of caregiver burden is a function of objective demands, such as the amount of time spent providing care and, perhaps more importantly, the caregiver’s subjective appraisal of the demands imposed relative to their own capacity, the patient’s status, and the caregiving environment. 15 -22 Assessment of caregiver burden often focuses on the caregiver’s perceptions of distress, role captivity, impact, or impairment attributable to the perceived demands of fulfilling the caregiver role. 19,23 -26 Although these measures of burden are widely used and supported in the literature, they may be limited in that they assess burden independent of patient functional status, as perceived by the caregiver. For example, existing instruments may capture caregiver-reported distress as it relates to difficulty communicating with the patient, but, to our knowledge, no currently available measure captures the caregiver’s perception of the patient’s functioning as it relates specifically to the patient’s communication abilities, social interaction, and executive abilities. Studies examining caregiver burden tend to measure caregivers’ function and patients’ function with 2 independently developed instruments that may be completed at different points in time. For example, the caregiver burden may be assessed using a caregiver self-report about their ability to function while the patient’s functional ability may be assessed by a physician. This approach fails to directly link the impact of the patient’s functional status on the caregiver’s perception of burden while actually communicating and interacting with the patient. It fails to capture the level of reward or frustration experienced by the caregiver from the interaction and does not assess how this experience affects the caregiver’s perception of burden.

The newly developed Caregiver-Perceived Burden Questionnaire (CPBQ) was designed to assess the caregiver’s perceptions of burden and patient functioning. The overall goal of using this novel measurement approach was not only to capture the caregiver’s burden but to relate changes in the patient’s function to the assessment of burden. In clinical settings or in clinical studies one could use the CPBQ to assess whether a given improvement in patient function is sufficient to lighten the burden on the caregiver, or whether improvement in a specific domain in patient function is more likely to reduce burden compared to similar improvements in other domains.

Methods

Development of a Conceptual Framework and Initial Item Pool

The assessment goals and measurement domains of the new questionnaire were initially informed via input from clinicians experienced in treating AD. The intent of these discussions was to identify key aspects of patient functioning that may be affected by pharmacologic treatment and, in the opinion of the clinicians, related to caregiver perceptions of burden. Once identified, these domains were then translated into a conceptual framework detailing the measurement domains and the hypothesized relationships among them.

Communication was identified by the clinicians as a key marker for disease severity and as a factor that could impact caregiver burden—an observation supported in the literature. 27 -30 Clinicians stated that, in their experience with caregivers, voluntary and meaningful communication was indicative of treatment success from the caregiver perspective, whereas involuntary or incoherent communication was a marker for disease progression that negatively impacted the interaction between the patient and the caregiver and therefore could create the perception of increased burden. Based upon this finding, we developed a functional communication domain that comprised caregiver-assessed voluntary communication, nonverbal communication, and uncontrolled or incoherent verbal communication.

Social interaction between patient and caregiver was identified by clinicians as a clinically relevant concept that is important to caregivers and may be responsive to treatment. 31 Further, the patient’s ability to initiate and engage in social activities may influence the way a caregiver perceives the patient’s condition and, for example, as a result of a rewarding interaction with the patient, the caregiver’s perception of burden may change. Positive social interactions and a perception of mutuality between caregiver and patient may be associated with perceptions of caregiver reward as opposed to caregiver burden. 32,33 To assess this aspect of patient functioning, items were drafted that measured social engagement and cooperativeness as perceived by the caregiver.

Executive dysfunction in relation to a patient’s ability to anticipate and prepare for scheduled or routine daily activities was identified as another key marker of clinical severity and source of caregiver burden. Impaired executive functioning has been associated with a higher probability of disease progression. 34 Executive dysfunction has also been associated with decreased initiation and execution of ADLs, which may be a source of caregiver-perceived burden. 20,35 -37 To assess this aspect of AD and the caregiving experience associated with it, we used a combination of items designed to assess the caregiver’s perceptions of the patient’s ability to plan and execute nonspecific activities, such as anticipate and prepare for his or her next activity.

The initial CPBQ item pool consisted of 45 items (Table 1). Of these, 42 used Likert-type response scales to measure caregiver perceptions of both the patient and themselves in relation to the patient. Caregiver-perceived patient functional communication, social abilities, and executive functioning formed the basis for the conceptual framework. Caregiver perceptions of impact on the patient and on themselves for each domain, along with an overall assessment of perceived burden, completed the conceptual framework (Figure 1). Three items used open-response fields to capture caregiver-reported patient engagement as a function of time spent engaging in sensible conversations, planning activities, and participation in activities. These questions had quantitative response options (time elapsed) and were not designed to be part of the final questionnaire; their role was to serve as a quantitative validation to the qualitative responses provided by the caregivers. The questionnaire was completed by caregivers as part of a clinical trial examining the safety and efficacy of extended-release (ER) memantine (NCT00322153). Data from this trial were used to select the final item pool and validate the questionnaire.

Table 1.

The Caregiver-Perceived Burden Questionnaire (CPBQ) Items Organized by final Domains

Caregivers’ Assessment of Patients (CAP) Scale
Item 1—Talkative (past month)a Item 20—Patient ability to understand what caregiver says affects patient daily life
Item 2—Talkative (compared to one month ago) Item 21—Trouble understanding what he or she saysa
Item 4—Talkative impacted his or her daily life (past month)a Item 23—Caregiver ability to understand what patient says affects patient daily life
Item 5—Initiate conversationa Item 24—Difference in speech
Item 6—Respond to conversationa Item 25—Reminded of activity on typical day
Item 8—Sustain interest in conversationa Item 26—Anticipate and prepare next activitya
Item 9—Spontaneous jokes or funny remarksa Item 29—Anticipation of next activity affects his or her lifea
Item 11—Conversation affects his or her daily lifea Item 30—Engage in fun activitiesa
Item 12—Respond nonverballya Item 32—Cooperate in social activitiesa
Item 13—Appropriate/inappropriate nonverbal Item 34—Engage in social activities affects his or her lifea
Item 14—Repeat same utterances Item 35—Connect to peoplea
Item 15—Repeat or echo something said Item 36—Acknowledge friendly behaviora
Item 16—Make up wordsa Item 37—Need encouragement to cooperate
Item 17—Trouble expressing themselvesa Item 39—Ability to cooperate affects his or her lifea
Item 18—Trouble understanding what is saida
Caregivers’ Assessment of Themselves (CAT) Scale
Item 3—Patient talkativeness impacts caregiver daily life (degree over the past month) Item 38—Patient ability to cooperate affects caregiver lifea
Item 10—Patient conversation affects caregivers daily lifea Item 40—Ease of providing carea
Item 19—Patient ability to understand affects caregiver lifea Item 41—Caregiver mental healtha
Item 22—Understanding patient affects caregiver lifea Item 42—Caregiver physical healtha
Item 28—Patient anticipation of next activity affects caregiver lifea Item 43—Caregiver ability to function at homea
Item 33—Patient engagement in social activities affects caregiver lifea Item 44—Caregiver ability to function at work
Caregiver global assessment
Item 45—Caregiver ability to function at home/work and physical/mental health affected by change in patient functioningb
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a Included in the final CAP and CAT scales.

b Retained in the final CPBQ but as an independent global assessment item and not as a part of the CAT scale.

Figure 1.

Figure 1.

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CPBQ conceptual framework.

Participants

The study sample consisted of 676 patients with moderate-to-severe AD (Mini-Mental State Examination [MMSE] scores ≥3 and ≤14), ≥50 years of age, and their caregivers. The study was a multinational, randomized, double-blind, placebo-controlled trial designed to investigate the safety and efficacy of ER memantine (28 mg/d, once daily). Study centers were located in the United States, Argentina, Chile, and Mexico. Participants with dementia complicated by another disease, Modified Hachinski Ischemia scores >4, other neurologic disorders, alcoholism, histories of drug abuse, and/or those treated with a depot typical neuroleptic within 6 months of screening were excluded from participation. The study was reviewed and approved by local institutional review boards or ethics committees prior to data collection. Written informed consent to participate in the study was obtained from the caregivers, patients, or their legally authorized representatives prior to conducting any study-related procedures. Verbal consent was obtained from participating patients who were unable to provide written consent.

Assessments

Patients and caregivers completed 7 study visits. Participant eligibility, including MMSE 38 and Functional Assessment Staging Tool (FAST) 39 scores, were assessed at screening. The CPBQ, MMSE, Severe Impairment Battery (SIB), 40 Alzheimer’s Disease Cooperative Study–Activities of Daily Living Scale for Severe Impairment (ADCS-ADL19), 41 Verbal Fluency Test (VFT), 42 and the Clinician’s Interview-Based Impression of Change-Plus Caregiver Input (CIBIC-Plus) were administered at baseline and at weeks 4, 12, and 24. The Neuropsychiatric Inventory (NPI) 43 and the MRUD-Lite, a modified form of the Resource Utilization in Dementia (RUD-Lite), 44 which included questions taken from the MacArthur Health and Performance Questionnaire, 45 were administered at baseline and at weeks 12 and 24.

Statistical Analyses

All validation analyses were conducted using data pooled from both memantine and placebo treatment groups. Demographic and clinical characteristics of patients and caregivers were examined using the baseline data.

The descriptive statistics and performance characteristics of CPBQ items were calculated using the baseline data. Items were flagged for possible removal if the item showed a floor (minimum response >50%) or ceiling (maximum response <50%) effect. Items were also flagged when the interitem correlation was greater than .80 or the item-total correlation was less than .20, indicating that the item provided poor or no additional information.

Exploratory factor analyses (EFAs) were conducted with the entire CPBQ item pool using a split-half sample. Oblique rotation was used. Items were selected based on 2 criteria (1) the largest factor loading of an item should be >0.3; and (2) this largest loading should be at least twice as large as the second largest loading of that item. Items that did not load into any factor (ie, all loadings <0.3), or that loaded into multiple factors (largest loading is not at least twice as large as the second largest loading), were flagged as candidates for deletion. Confirmatory factor analysis (CFA) was used to confirm the factor structure established in the EFA. The CFA was conducted using the second split-half sample. The model was assessed with comparative fit index (CFI), root mean square error of approximation (RMSEA), and standardized root mean square residual (SRMR). A CFI >0.95, RMSEA <0.05, and SRMR <0.05 were considered a good fit.

Rasch model analysis was used to determine the degree to which the CPBQ items exhibited appropriate measurement properties—specifically, the Guttmann scaling properties of properly ordered response options. Under the Rasch model, items that did not fit the model well were tentatively excluded from the set; the evaluation process was repeated until all remaining items showed good model fit.

Items with poor psychometric properties as identified in the item, factor, and Rasch model analyses were flagged for removal. Each item, including items flagged for removal, was evaluated by the AD clinical experts based on face validity and clinical significance. Psychometrically poor items lacking clinical significance or with poor face validity were removed from subsequent analyses of the CPBQ. Upon finalizing the CPBQ, a scoring algorithm based on Rasch logit was developed to create a scale score with a mean value of 5 and a standard deviation (SD) of 1.

The reliability and validity of the final CPBQ measure was assessed using baseline data. Internal consistency reliability was assessed for all scales using the Person Separation Index (PSI), which is analogous to Cronbach α; values ≥.70 are considered acceptable evidence of internal consistency. 46,47 Test–retest reliability between baseline and week 4 was examined among stable patients (“no change” on CIBIC-Plus). Reproducibility was evaluated using intraclass correlation coefficient (ICC), with values >.6 being considered acceptable.

Concurrent validity was evaluated by examining the relationship between the CPBQ scales and the NPI, SIB, ADCS-ADL19, CIBIC-Plus, and FAST using Spearman correlations. Analyses were completed with the assumption that concurrent validity would be demonstrated if the CPBQ was substantially correlated (|>.30|) with other instruments measuring similar concepts.

Known group validity was assessed by classifying patients into groups according to the baseline MMSE and SIB scores. Analysis of covariance (ANCOVA) was used to examine the known groups’ validity with age, gender, and duration of diagnosis (baseline visit date–date of diagnosis) as covariates. Patients were grouped by MMSE into categories of moderate AD (MMSE ≥10) and severe AD (MMSE <10) and also by SIB tertile scores (mild: ≥88; moderate: 75-87; severe: ≤74).

Responsiveness analysis was conducted using ANCOVA. The CPBQ change scores (baseline to week 24) for caregivers of patients with a CIBIC-Plus rating of “no change” or worse (nonresponders) were compared with the change scores of those reporting higher than “no change” (responders). Comparison of responders versus nonresponders was conducted using age, sex, and baseline score as covariates.

Guidelines for interpretation of change scores were developed by examining the CPBQ minimal important difference (MID). Consistent with previous work in this area, 48 MID was defined as the minimum score change that is meaningful for patients or clinicians, rather than mere statistical significance. CPBQ MID was determined by calculating the mean change, percentage change, and effect size associated with CIBIC-Plus ratings. Specifically, the effect size and percentage change for those rated as experiencing “minimal improvement” on the CIBIC-Plus were used to determine what minimum amount of change in CPBQ score equated to an MID.

Results

Participants

Patients’ age ranged from 49 to 97 years, with a mean ± SD of 76.5 ± 8.1 years. Patients were mostly female (72%), Hispanic (69%), and identified themselves as Caucasian (94%). The average MMSE score was 10.7 ± 2.9. Most of the patients were in FAST stages 4 through 7a, with the highest concentrations in stages 4 (23.2%) and 5 (25.1%). Caregivers’ age ranged from 18 to 93 years, with a mean age of 58.2 ±15.6. Females accounted for 71% of caregivers. Caregivers were typically either a child (39%) or a spouse (37%) of the patient and most often (75%) lived with the patient. Most caregivers (74%) reported providing daily care to the patient, with 60% reporting that they provided more than 7 hours of care a day to the patient on average in the week prior to baseline.

Psychometric Evaluation and Item Selection

Descriptive statistics were calculated for each CPBQ item. Three items had a floor effect (all patients scored >50%), 2 had low item-total correlation (<.2), and 2 items had high interitem correlation (>.8). No items showed a ceiling effect.

The EFA was conducted with the entire CPBQ item pool using a split-half sample. The factors suggested by the EFA results deviated from the draft conceptual framework originally hypothesized by the developers. Based on further review of the results and the item content, and with the consideration of clinical experts, the CPBQ was divided into 2 scales: the Caregivers’ Assessment of the Patient (CAP) and the Caregivers’ Assessment of Themselves (CAT). The CAP was conceptualized as a measure of caregiver-perceived patient functional engagement, whereas the CAT scale was conceptualized as a measure of caregiver-perceived burden in relation to the patient’s engagement. Subsequent to this division, additional EFAs were run on each hypothetical scale. The EFA for the CAP began with 29 items related to the caregiver’s perception of the patient. Review of the factor analyses found that the 3-factor solution for the CAP was most suitable.

Excluding items that did not meet the factor loading selection criteria (>0.3), 20 items were retained for the CAP. The CFA conducted based on the 3-factor solution using the other split-half sample showed CFI = 0.863, MRSEA = 0.073, and SRMR = 0.065. The fit statistics did not meet the goodness-of-fit criteria, but the construct of the items were judged by the experts as the most plausible and meaningful. The CAT scale started with 13 items for the EFA. Review of the factor analyses found that the 2-factor solution for the CAT was most suitable. Examining the factor loadings of the 2-factor solution resulted in retention of 10 items that met the criteria. The CFA conducted based on the 2-factor solution using the other split-half sample showed CFI = 0.918, MRSEA = 0.084, and SRMR = 0.056. The fit statistics did not meet the goodness-of-fit criteria, but the construct of the items was judged by the expert clinicians to be the most plausible and meaningful.

After the factor analysis, Rasch model analysis was conducted for the remaining 20-item CAP and the 10-item CAT. Both the CAP and CAT showed good overall fit to the Rasch model, and thus the 20-item CAP and 10-item CAT were finalized (Table 1). Scoring algorithms were developed for the final 20-item CAP and 10-item CAT. First, 12 items were reverse scored accordingly, so that the lower score indicates less burden and better function. Raw summed scores were then calculated for CAP and CAT. Separately, raw summed score to Rasch scale score conversion tables were developed by linear transformation of the Rasch logit scores. The raw summed scores were then used to obtain the corresponding Rasch scale scores from the conversion tables. The Rasch scale scores of the CAP and CAT were used for further validation of the CPBQ measure.

Validation of the Final CPBQ Measure

Reliability

The PSI was used to examine the internal consistency of the CPBQ. The PSI was 0.89 for the CAP Rasch scale score and 0.83 for the CAT Rasch scale score (Table 2). Cronbach’s α was .88 for the CAP and .83 for the CAT. The PSI and Cronbach’s α levels were considered adequate evidence of internal consistency for both scales. The reproducibility of the CPBQ was examined using ICC. The CAP Rasch score had an ICC (0.83) that showed an adequate level of reproducibility. The ICC (0.58) for the CAT Rasch score was not as high (Table 2).

Table 2.

Measurement Properties of the CPBQ Subscales

Parameter CPBQ subscales
CAP CAT
Reliability
Person Separation Index .89 .83
Cronbach’s α .88 .83
Intraclass correlation .83 .58
Convergent validity, correlation r(P value [H0: r = 0])
NPI .38 (<.001) .35 (<.001)
SIB −.45 (<.001) −.19 (<.001)
ADCS-ADL19 −.57 (<.001) −.24 (<.001)
CIBIC-Plus .45 (<.001) .23 (<.001)
FAST 2 .36 (<.001) .14 (<.001)
MMSE −.37 (<.001) −.12 (<.05)
Known Groups Validity, P valuea
Moderate (MMSE ≥10) vs. Severe AD (MMSE <10) <.001 <.01
Between severe (SIB ≤74), moderate (SIB 75-87), and mild (SIB ≥88)c 1: <.001 1: .0726
2: <.001 2: <.001
3: <.001 3: .0560
Responsiveness, P valued
CIBIC-Plus: “responders” (ratings 5-7, improvement) vs “nonresponders” (ratings 1-4, decline or no change) <.001 <.001
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Abbreviations: AD, Alzheimer’s disease; ADCS-ADL19, the 19-Item Alzheimer’s Disease Cooperative Study–Activities of Daily Living Scale; ANCOVA, analysis of covariance; ANOVA, analysis of variance; CAP, Caregivers’ Assessment of Patients; CAT, Caregivers’ Assessment of Themselves; CIBIC-Plus, Clinician’s Interview-Based Impression of Change–Plus Caregiver Input; CPBQ, Caregiver-Perceived Burden Questionnaire; FAST, Functional Assessment Staging of Alzheimer’s Disease; MMSE, Mini-Mental State Examination; NPI, Neuropsychiatric Inventory; SIB, Severe Impairment Battery;.

a Analyzed using ANOVA.

b Assessed at visit 1 (screening).

c 1 = Severe vs moderate; 2 = Severe vs Mild; and 3 = Moderate vs Mild.

d Analyzed using ANCOVA, controlling for age, sex, and baseline CPBQ score.

Validity

Concurrent validity

The concurrent validity of the CAP scale was well supported (Table 2). Correlations between the CAP scale and the NPI, SIB, ADCS-ADL19, CIBIC-Plus, FAST, and MMSE were |>.30| and were significant (P < .001).

Known groups’ validity

Both MMSE and SIB were used to assess the known groups’ validity of the CPBQ scales. The MMSE severity groupings (baseline) were used to create groups. Patients were split into 1 of 2 groups: MMSE score <10 (mean CAP score 5.3; SD = 0.06) and ≥10 (mean CAP score 4.7; SD = 0.04). Comparison of the CAP Rasch score means using ANCOVA found that they were significantly different (P < .001), thus indicating an adequate level of known groups validity (Table 2). Using the same MMSE groupings, the mean CAT Rasch scores were 5.7 (SD = 0.09) for the <10 group and 5.3 (SD = 0.06) for the ≥10 group. As with the CAP, the comparison of these means supported the known groups’ validity of the CAT (P = .002).

Known groups’ validity was also examined by categorizing the sample into SIB severity tertiles: severe (SIB ≤74), moderate (SIB 75-87), and mild (SIB ≥88). The pairwise comparison results (Table 2) supported the known groups’ validity of the CAP scale, all 3 possible comparisons among the groups were significantly different (P < .0001). Results were more mixed for the CAT scale, the scale only showed significant discrimination between the known groups of mild and severe (Table 2).

Responsiveness

The ANCOVA comparing the mean CAP Rasch change score of the responders (least square mean = −0.4; standard error = 0.05) against those of the nonresponders (least square mean = 0.1; standard error = 0.04) were found to be significant (P < .001) after controlling for age, gender, and baseline CPBQ scores. The ANCOVA, comparing the change scores of the CAT Rasch score between the responders (least square mean = −0.9; standard error = 0.10) and nonresponders (least square mean = 0.0; standard error = 0.07), were significant (P < .001) after controlling for age, gender, and baseline CPBQ scores.

Minimal Important Difference

The MID values for the CAP and CAT scales were determined by examining the mean baseline to week 24 change scores associated with a CIBIC-Plus rating of “minimal improvement.” Using Rasch scale scores, the mean change associated with clinical assessment of “minimal improvement” was −0.3 (SD = 0.62) for the CAP and −0.7 (SD = 1.44) for the CAT. These changes represented a 4.9% change for the CAP and an 8.5% change for the CAT with effect sizes of 0.36 and 0.60, respectively. For these reasons, the CAP Rasch scale score and CAT Rasch scale score MID values were determined to be 0.3 and 0.7, respectively.

Discussion

The CPBQ presents a novel approach to measuring caregiver burden in relation to perceived patient functioning. In creating the CPBQ, we sought to design a cohesive measure that captured, through the eyes of the caregiver, both the caregiver’s perception of burden and patient’s level of functioning, to give a more complete picture of the burden experience and to better understand how the patient’s perceived functional status affects perceived burden. This more comprehensive method of measuring burden experience is advantageous from a measurement perspective in that such a tool is capable of elucidating the relationship between caregiver perceptions of burden, and specific domains of patient functioning that may be improved by treatment. By capturing the caregiver’s perception of both self and patient, the idea is that potential changes in caregiver-perceived burden could be better understood as they relate to the patient’s impact on the caregiver. This comprehensive approach, emphasizing the dyadic nature of caregiving, differentiates the CPBQ from other measures. Although other caregiver burden assessment instruments measure a wide array of concepts, they fail to relate the caregiver’s perception of the patient’s function to the perceived burden. The psychometric analysis of data showed the 2 unidimensional scales of the CPBQ to be reliable, valid, and responsive. The 20-item CAP scale and 10-item CAT scale showed adequate psychometric measurement properties, suggesting that the Rasch scored scales are suitable for assessing caregiver burden and provide a means for understanding the inter-relationship between the domains of patient function and the perception of burden as perceived by the caregiver.

Limitations

The primary limitation of this study and the CPBQ development process was the lack of caregiver input prior to drafting the conceptual framework and items. The CPBQ was developed as an exploratory attempt to elucidate the relationship between caregiver perceptions of patient function and their own perceptions of burden within the context of a clinical trial. Historically many instruments, especially those developed with an exploratory intent, were developed without caregiver/patient input and this was the case with the CPBQ which was developed in collaboration with AD clinicians. It is now recommended that the conceptual framework of any newly developed patient-reported outcomes (PROs) or caregiver-reported outcomes (CROs) be informed by qualitative studies to ensure that it reflects the perspective and disease experience of the population who will be completing the questionnaire. 49,50 This is of particular importance if the PRO or CRO under development is intended for a product label or claim. 51 Patient input is commonly collected by conducting interviews or focus groups designed to elicit the domains that are relevant and important to patients or, in the case of CROs, caregivers’ input should be sought to ensure content validity. Much qualitative research has been published since the development of the CPBQ. Thus, it is possible now, in some cases, to ascertain the domains relevant to AD caregivers from these published literatures. In the case of CPBQ, although direct feedback from caregivers was not obtained during its development, post hoc review of the literature reporting on interviews with caregivers supports that the domains assessed in the CPBQ are relevant to patients and perceived by caregivers to be important. 27,49,52,53

The three measurement domains of the CPBQ are supported by existing literature on qualitative research with caregivers. Garity and colleagues 27 interviewed 18 participants, caregivers of family members with AD, and reported that the loss of a patient’s ability to communicate represented a significant amount of stress or burden to the caregiver; these findings have also been supported and referenced by Wheeler et al. 53 These same qualitative studies also describe the importance of positive interactions between the patient and caregiver, supporting the concept that social interaction affects the caregiver’s perception of burden. 27,53 Frank et al included caregiver feedback in the development of the dependence scale and reported that assisting with routine chores/household activities was one of the main themes related to the burden of care. 49 In another qualitative study of 17 caregivers, patient dysfunction in basic, routine activities was reported as a main source of strain or burden among caregivers. 52 Collectively, these studies suggest that the concepts measured by the CPBQ are relevant aspects of the caregiver burden experience.

Although the evidence drawn from the literature suggests the CPBQ measures concepts relevant to caregivers, the authors recognize the need for well-designed qualitative studies with caregivers to support the content validity of the questionnaire. Such work may refine the content of the CPBQ or identify additional domains that are important when considering the patient–caregiver relationship with respect to burden. Additionally, future validation studies should consider including all AD severities to support the generalizability of the results and include other validated measures of caregiver burden to assess the concurrent validity of the CPBQ.

Conclusions

The CPBQ appears to be a reliable, valid, and responsive measure that assesses the level of patients’ functioning and the level of caregiver-perceived burden in clinical trials of moderate-to-severe AD. These results suggest that (1) it is feasible to develop a caregiver burden questionnaire that assesses, at the same point in time, the caregivers’ perceptions of the patients’ functional status and the corresponding perceived caregiver burden; (2) the approach taken to develop the CPBQ warrants further consideration; and (3) future work with caregivers to further establish the content validity of the CPBQ could result in an improved assessment of caregiver burden.

Acknowledgments

The authors thank William Rodman Shankle, MD, MS; Christine Thompson, BS; Michelle Mocarski, MPH; and Ren Yu, MA, for their contributions to this study. The authors thank the funding support provided by Forest Laboratories, Jersey City, New Jersey.

Footnotes

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding: The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: M. Haim Erder and Juliana Setyawan were employed by Forest Research Institute during the conduct of analysis, but are currently employed by Shire Pharmaceuticals. Shire Development LLC was not associated with this study. Drs Chen and Wilcox are employed by United BioSource Corporation (UBC), which provides consulting and other research services to pharmaceutical, device, government, and nongovernment organizations. In this salaried position, they work with a variety of companies and organizations and are precluded from receiving payment or honoraria directly from these organizations for services rendered. Similarly, Mr O’Quinn was also a UBC employee during the preparation of this manuscript but is currently employed by MedImmune, LLC. MedImmune, LLC was not associated with this study.

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