Validity and Reliability of the German Quality of Life–Alzheimer’s Disease (QoL-AD) Self-Report Scale

Abstract

Background:

The Quality of Life–Alzheimer’s Disease (QoL-AD) scale is a widely used measure of quality of life (QoL) in dementia. Although the instrument has been validated in several languages, the psychometric properties of the German self-report version have not yet been analyzed.

Objective:

This study examines the internal consistency, test-retest reliability, and construct validity of the German QoL-AD self-report scale.

Methods:

The sample included 30 patients suffering from mild to moderate Alzheimer’s disease or vascular dementia (19 females; mean age 77.3 years; mean Mini-Mental State Examination (MMSE) score 19.7 points). To determine test-retest reliability, the QoL-AD self-report scale was re-administered four to seven days apart. For construct validity analysis, the Dementia Quality of Life instrument (DQoL), Geriatric Depression Scale (GDS), MMSE, and an adapted short form of the Neuropsychiatric Inventory (NPI) were used.

Results:

The German QoL-AD self-report scale shows an internal consistency of α= 0.79 and a test-retest reliability of r = 0.75 (p < 0.01). Regarding construct validity, there was a significant positive correlation between the total scores of the QoL-AD and DQoL (r = 0.47, p < 0.05). The analysis revealed no significant correlations with the GDS or the adapted NPI. No association could be observed between the QoL-AD and the MMSE (r = 0.01), confirming divergent validity.

Conclusion:

The results indicate that the German QoL-AD self-report scale is a suitable instrument for assessing QoL in patients suffering from mild to moderate dementia, thus supporting its use in clinical practice and research.

Keywords

Alzheimer’s disease dementia Germany quality of life reliability and validity self report

INTRODUCTION

Dementia is one of the most common mental disorders in later life [1]. Due to demographic changes, the prevalence of dementia is rapidly increasing: in 2018, around 50 million people worldwide suffered from this neurodegenerative disease and this number is expected to increase to 152 million by 2050 [2]. As no cure is available yet, the main goal is to preserve and enhance the quality of life (QoL) of patients suffering from dementia [3].

QoL is a broad construct, but there is currently no generally accepted definition [4]. Neumann et al. [5] stated that in neurological studies the most widely used definition was given by the World Health Organization (WHO). The WHO described QoL as the “individuals’ perception of their position in life in the context of the culture and value systems in which they live and in relation to their goals, expectations, standards and concerns” [6:1405]. In dementia research, many authors refer to the multidimensional conceptualization by Lawton [7, 8]. This model of QoL in dementia includes subjective and objective dimensions in four overlapping sectors: 1) behavioral competence (e.g., activities of daily living and cognitive status), 2) objective environment (e.g., living situation in nursing homes), 3) psychological well-being (e.g., mental health and positive/negative emotions), and 4) perceived QoL, which is characterized as subjective perception of the behavioral competence dimensions [7, 8].

The assessment of QoL in dementia allows clinicians to consider the patients’ individual life situation and to align treatment decisions to the patients’ preferences [9]. Moreover, QoL can be regarded as an appropriate outcome variable in intervention studies for determining clinical relevance [10, 11]. As part of the growing field of research, numerous QoL measures have been developed. QoL can be assessed using generic or condition-specific instruments. Condition-specific measures seem to be more responsive to clinical changes, therefore emphasis should be placed on instruments developed for use in dementia patients when focusing on this specific population [3, 12]. Dementia-specific QoL instruments are based on three assessment methods: direct observation of the patient’s behavior, proxy report by caregiver or family member, and/or the patient’s self-report [13]. Many authors agree that people in stages of mild to moderate dementia are able to rate their own QoL (e.g., Logsdon et al. [14] and Brod et al. [15]). Several factors are discussed to be related to the patients’ self-reports. There is evidence that better QoL ratings by the patients with dementia are associated with less depression, greater anosognosia, fewer neuropsychiatric symptoms and the use of anti-dementia drugs [16 –18]. Numerous studies have found no association between self-reported QoL and the severity of the patients’ cognitive impairment [13 , 19–22]. Since QoL is primarily a subjective construct, the patients self-report should be the preferred method. This is also important for ethical reasons, as it respects the self-determination and autonomy of patients suffering from dementia [13]. In more advanced dementia stages, it may be necessary to seek QoL scores from both, the patient and caregiver perspectives to gain maximum insight [23].

An instrument that meets these requirements is the Quality of Life–Alzheimer’s Disease (QoL-AD) scale [13, 14]. The QoL-AD was developed to assess QoL specifically in patients with Alzheimer’s disease and is considered to be the measure of choice in European intervention studies [24]. It provides a self-report version, which is administered in interview format, and a proxy report version, which can be completed by caregivers as a questionnaire. The two scales can be used separately but also a weighted composite score can be calculated [14]. Over the past 20 years, the QoL-AD has been translated into several languages. The psychometric properties of the self-report scale have been confirmed in 18 countries, with recent validation studies being conducted in Malaysia [25] and the Czech Republic [26]. In the previous evaluations, reliability was assessed by internal consistency; in addition, most authors performed analysis on test-retest reliability. Validity was mainly determined by construct validity, using generic and condition-specific QoL measures or related instruments, such as measures of depression, neuropsychiatric symptoms, and cognition.

For the German translation, only the psychometric properties of the QoL-AD proxy version and inter-rater agreement between the two versions have been investigated [27 –29]. As far as we know, the reliability and validity of the German QoL-AD self-report version have not yet been proven. Therefore, the objective of this study was to investigate the internal consistency, test-retest reliability, and construct validity of the German QoL-AD self-report scale. We hypothesized that the German translation will reveal an acceptable internal consistency and high test-retest reliability. Regarding construct validity, we put forth the following hypotheses:

There will be a significant positive correlation between the QoL-AD self-report scale and the Dementia Quality of Life instrument (DQoL) [15], which also measures QoL in dementia via self-report (convergent validity I).

There will be a significant negative correlation between the QoL-AD self-report scale and the presence of depressive and neuropsychiatric symptoms, which are factors assumed to be associated with QoL in dementia (convergent validity II).

Since the severity of cognitive decline does not seem to be a predictor of self-reported QoL [16], we hypothesized no correlation between the QoL-AD self-report scale and cognitive status (divergent validity).

MATERIALS AND METHODS

Study design

The cross-sectional study was primarily conducted at the Department of Geriatric Psychiatry and Psychotherapy of the ‘Landschaftsverband Rheinland’ Hospital (LVR-Hospital) in Cologne (n = 27). In addition, participants were recruited at an outpatient practice for speech and language therapy in Cologne (n = 1) and an outpatient practice for general medicine in Thuringia (n = 2). The data collection took place over a six-month period.

Ethics approval was obtained from the ethics committee of the Medical Chamber North-Rhine (reference no. 2018192). All participants were informed about the study objectives. Patients provided written informed consent if they had a Mini-Mental State Examination (MMSE) score of at least 20 points and were able to repeat the study content in their own words [30]. In all other cases, the legal representatives signed the informed consent.

Participants

Inclusion criteria for the participants were as follows: 1) diagnosis of dementia in Alzheimer’s disease or vascular dementia according to ICD-10 criteria; 2) MMSE score≥10; and 3) German as first language or fluency in the German language. Exclusion criteria were: 1) diagnosis of dementia in other diseases, schizophrenia or organic hallucinosis; 2) acute delirium; 3) diagnosis of aphasia or severe impairments of productive and receptive speech and language abilities according to clinic staff members; 4) severe hearing disorders that are not compensated by a hearing aid; and 5) severe behavioral symptoms that prevented the completion of the QoL-AD interview.

Instruments

Sociodemographic and clinical data were collected from medical records (gender, age, marital status, dementia diagnosis, number of comorbid diseases) and directly from participants (level of education). According to other QoL-AD validation studies [20–22 , 32], the translated German versions of the following instruments were used:

Quality of Life–Alzheimer’s Disease (QoL-AD) self-report scale [13, 14]

The QoL-AD questionnaire consists of 13 items that measure various domains of QoL (e.g., physical health and mood) as well as the patient’s self as a whole and QoL as a whole (see Table 2). All items can be answered on a consistent four-point scale (1 = poor, 2 = fair, 3 = good, 4 = excellent) by considering the patient’s current QoL. Total scores range between 13 and 52 points, with higher scores reflecting better QoL. For the QoL-AD self-report interview, detailed instructions are given to the interviewer. The measure has an administration time of approximately 10 minutes and uses simple language to increase feasibility in patients suffering from dementia. According to the authors, the reliability and validity of the QoL-AD is proved in patients with mild to moderate dementia [13, 14]. Nevertheless, Hoe and colleagues [33] report that the instrument can also be used in patients with severe dementia (MMSE score of at least three points). We used the German translation by Mapi Research Trust [34].

Dementia Quality of Life instrument (DQoL) [15]

The DQoL is a patient-rated dementia-specific QoL measure administered in interview format. It consists of 29 items structured in five subscales (positive affect, negative affect, self-esteem, feelings of belonging, and sense of aesthetics) and one additional item about the patient’s overall QoL. The items are scored on a five-point scale. Higher scores indicate a better QoL, except for the negative affect subscale [15, 35]. The reliability and validity of the German translation was examined by Voigt-Radloff et al. in 2012 [35].

Mini-Mental State Examination (MMSE) [36]

The MMSE is a widely used screening instrument for cognitive status. Total score ranges from 0 to 30, with higher scores indicating better cognitive functioning [36]. Information on the diagnostic quality of the MMSE in German geriatric and psychiatric patients is provided by Beyermann et al. [37] and Burkart et al. [38].

Geriatric Depression Scale (GDS), short form [39]

The GDS is a patient-rated screening instrument for measuring depressive symptoms in older adults, originally consisting of 30 items [40]. We administered the 15-item short form (score range 0–15), in which higher scores indicate more depressive symptoms [39]. For its German translation, Gauggel and Birkner [41] reported a cut-off score of six points to distinguish persons with depression from non-depressed older adults (sensitivity 84.0%, specificity 88.9%).

Neuropsychiatric Inventory (NPI), adapted short form [42]

The NPI provides information about behavioral and neuropsychiatric symptoms in patients suffering from dementia. In an interview, caregivers rate the presence, severity, and frequency of 12 symptom categories (e.g., delusions, anxiety, or aberrant motor behavior) as well as their own distress [42]. In order to ensure feasibility in routine clinical practice, we adapted the original NPI into a short-form questionnaire and used it as a screening for the presence of neuropsychiatric symptoms. This adapted short form contains only the NPI screening questions with a yes/no-answer format. Every yes-answer was scored with 1 and every no-answer with 0. The adapted short form provides a minimum score of 0 and a maximum score of 12, with every point corresponding to the presence of a symptom.

Procedure

Data collection was accomplished by the first author. The QoL-AD, DQoL, GDS, and MMSE were performed individually with each participant, using the paper-and-pencil method. The location varied depending on the recruitment situation: at the LVR-Hospital, data collection took place in a therapy room or in the patient’s room; at the practice for speech and language therapy, measurement was conducted after regular therapy in the therapy room; at the practice for general medicine, the participants were visited at home for data collection. During administration, ambient noises were minimized. The full measurement required approximately one hour. Depending on the patients’ capacity, the measures were carried out either on the same day or spread over up to three days. To assess test-retest reliability, the QoL-AD was administered again four to seven days apart, in a group of 27 participants. On average, 5.56 days (SD = 1.37) elapsed between time points 1 and 2. Only for the patients of the LVR-Hospital (n = 27) was the adapted NPI short form completed by the caregiver. Caregivers needed about five minutes to complete the questionnaire.

Data analysis

Data analysis was conducted using IBM SPSS Version 25.0.0.2 for Windows. We performed descriptive analysis to report the QoL-AD results and sample characteristics. To explore internal consistency, we calculated Cronbach’s alpha coefficient and applied guidelines from George and Mallery [43]: α> 0.90 = excellent; 0.90≥α> 0.80 = good; 0.80≥α> 0.70 = acceptable; 0.70≥α> 0.60 = questionable; 0.60≥α> 0.50 = poor; α< 0.50 = unacceptable. For analysis of test-retest reliability and construct validity, bivariate correlations were conducted by using Spearman’s correlation coefficient because the assumption of normal distribution was not fulfilled for all the analyzed variables [44]. Test-retest reliability was examined by the correlation of the QoL-AD total scores at time points 1 and 2. In terms of construct validity, the convergent validity was assessed by calculating a correlation coefficient for QoL-AD total scores and: 1) DQoL total scores and subscale scores, with negatively formulated items of the negative affect subscale coded in reverse order; 2) GDS total scores; and 3) adapted NPI total scores. Based on previous research [20, 22], we calculated the correlation between QoL-AD and MMSE to determine divergent validity. For the interpretation of correlation coefficients, guidelines of Hinkle, Wiersma, and Jurs [45] were used. All tests on statistical significance were two-tailed and p < 0.05 was considered significant. Additionally, we calculated confidence intervals using bootstrapping (N = 1000), which according to Field [44] is robust in terms of normal distribution. Here we used the BCa method (bias corrected and accelerated), which is recommended for reliability by Hayes and Scharkow [46].

RESULTS

Characteristics of the sample

A total of 139 patients diagnosed with Alzheimer’s disease or vascular dementia were screened for study eligibility. Out of these, 109 patients (78.4%) could not be included due to acute illness, early hospital discharge, absence of a legal representative, or no consent for participation. Therefore, a total of 30 patients (19 females) participated. Of these, 27 patients were recruited at the LVR-Hospital, two in the practice for general medicine, and one in the practice for speech and language therapy.

Table 1 shows sociodemographic and clinical characteristics of the sample. Patients’ mean age was 77.3 years (SD = 6.3). The mean MMSE score was 19.7 (SD = 4.8). Regarding dementia severity, 16 patients had mild dementia (MMSE scores≥20) and 14 patients suffered from moderate dementia (MMSE scores: 10–19). A GDS score of six points or more, suggesting the presence of depression according to Gauggel and Birkner [41], was achieved by 17 participants (56.6%). Neuropsychiatric symptoms were observed in 26 of the 27 participants (96.3%) for whom the adapted NPI short form was completed. The most frequent symptoms were: depression/dysphoria (59.3%), anxiety (44.4%), apathy/indifference (40.7%), and night-time behavior disturbances (40.7%).

Table 1

Patient characteristics

Variables	n	f (%)	M (SD)	Range
Age	30		77.30 (6.30)	66–90
Gender	30
Female		19 (63.3)
Male		11 (36.7)
Native language	30
German		29 (96.7)
Polish		1 (3.3)
Marital status	30
Single		3 (10.0)
Married		13 (43.3)
Divorced		6 (20.0)
Widowed		8 (26.7)
School-leaving qualification	26
No school-leaving certificate		12 (46.2)
Secondary school certificate (9th grade)		7 (26.9)
Secondary school certificate (10th grade)		2 (7.7)
University of Applied Sciences entrance qualification		2 (7.7)
University entrance qualification		3 (11.5)
Vocational qualification	26
No vocational qualification		4 (15.4)
Apprenticeship		16 (61.5)
Trade and technical school qualification		3 (11.5)
University degree		3 (11.5)
Diagnosis	30
Dementia in Alzheimer’s disease		25 (83.3)
Vascular dementia		5 (16.7)
Number of comorbid diseases	29		3.76 (2.43)	0–10
Clinical Measures
MMSE	30		19.67 (4.78)	11–28
GDS	30		5.97 (3.21)	0–14
Adapted NPI	27		3.48 (2.33)	0–11
QoL-AD self-report	30		34.27 (4.99)	24–44
DQoL	28		97.79 (20.04)	58–127

DQoL, Dementia Quality of Life instrument (30–150; higher scores indicate a better QoL); f, frequency; GDS, Geriatric Depression Scale (0–15; higher scores indicate more depressive symptoms); MMSE, Mini Mental State Examination (0–30; higher scores indicate a better cognitive status); NPI, Neuropsychiatric Inventory (0–12; higher scores indicate more neuropsychiatric symptoms); QoL-AD, Quality of Life–Alzheimer’s Disease (13–52; higher scores indicate a better QoL).

Descriptive results of QoL-AD

All participants (n = 30) completed the QoL-AD. The total scores ranged from 24 to 44, with a mean score of 34.3 (SD = 5.0). Both the median and the modal scores were 35.0.

The patients’ ratings on the 13 items of the QoL-AD are presented in Table 2. Most of the patients chose the category good to evaluate the various QoL domains. Only the patients’ energy was rated mostly with the category fair. Categories poor and excellent were chosen least often. For each two items, none of the participants chose these response options (living situation/money and physical health/memory).

Table 2

Patient ratings for the German QoL-AD self-report scale (n = 30)

	Poor	Fair	Good	Excellent
Item	n	n	n	n	Mean (SD)
1. Physical health	2	13	15	0	2.43 (0.63)
2. Energy	3	17	9	1	2.27 (0.69)
3. Mood	3	13	13	1	2.40 (0.72)
4. Living situation	0	6	16	8	3.07 (0.69)
5. Memory	5	11	14	0	2.30 (0.75)
6. Family	2	1	22	5	3.00 (0.69)
7. Marriage	3	4	17	6	2.87 (0.86)
8. Friends	2	6	19	3	2.77 (0.73)
9. Self as a whole	1	10	17	2	2.67 (0.66)
10. Ability to do chores around the house	2	7	20	1	2.67 (0.66)
11. Ability to do things for fun	6	7	16	1	2.40 (0.86)
12. Money	0	12	13	5	2.77 (0.73)
13. Life as a whole	1	10	17	2	2.67 (0.66)
Total	30	117	208	35

Bold text indicates modal values. Assignment of points: Poor = 1, Fair = 2, Good = 3, Excellent = 4. QoL-AD, Quality of Life–Alzheimer’s Disease.

Reliability

To assess internal consistency with Cronbach’s alpha, QoL-AD total scores of all participants (n = 30) were used. The analysis revealed a Cronbach’s alpha value of 0.79.

Due to hospital discharge during the retest interval, we examined test-retest reliability based on a smaller subsample of 27 participants. QoL-AD total scores of the subsample ranged from 24 to 44 (M = 34.4, SD = 5.1) at time 1 and from 21 to 45 (M = 33.5, SD = 5.5) at time 2. There was a significant, high positive correlation between the two time points of the QoL-AD interview (r = 0.75, p < 0.01, BCa 95% CI [0.488, 0.895]).

Construct validity

Construct validity results are shown in Table 3. Because two participants were unable to complete the DQoL, the first validity analysis is based on the data of 28 patients. There was a low but significant positive correlation between QoL-AD and DQoL total scores (r = 0.47, p < 0.05). The correlations of QoL-AD total scores and DQoL subscale scores reached a low to moderate level. Correlations with three of the five subscales were statistically significant: self-esteem (p < 0.01), feelings of belonging (p < 0.05) and positive affect (p < 0.05). As presented in Table 3, the QoL-AD showed a low negative correlation with GDS scores (n = 30) and a very low negative correlation with scores of the adapted NPI (n = 27). Neither of the correlations were statistically significant. There was no correlation between the QoL-AD and the MMSE (r = 0.01, n = 30).

Table 3

Spearman correlations between the German QoL-AD self-report scale and other measures to identify construct validity

			BCa 95%	CI
Instruments	n	r	LL	UL
DQoL^a	28	0.47*	0.082	0.756
Self-esteem	28	0.53**	0.246	0.716
Feelings of belonging	28	0.43*	0.106	0.679
Sense of aesthetics	28	0.32	−0.125	0.705
Positive affect	28	0.42*	0.031	0.715
Negative affect	28	0.32	−0.079	0.655
GDS^a	30	−0.34	−0.677	0.103
Adapted NPI^a	27	−0.22	−0.575	0.190
MMSE^b	30	0.01	−0.400	0.452

^aConvergent validity. ^bdivergent validity. *p < 0.05. **p < 0.01. BCa, bias corrected and accelerated; CI, confidence interval; DQoL, Dementia Quality of Life instrument; GDS, Geriatric Depression Scale; LL, lower limit; MMSE, Mini Mental State Examination; NPI, Neuropsychiatric Inventory; QoL-AD, Quality of Life–Alzheimer’s Disease; UL, upper limit.

DISCUSSION

In this study, we reported the psychometric properties of the German QoL-AD self-report scale for the first time. In our analysis, the QoL-AD showed an acceptable internal consistency, high test-retest reliability, and good construct validity, especially with regard to the divergent validity.

The descriptive results of the QoL-AD imply an overall good QoL for the patients suffering from dementia. As illustrated in Table 2, the most frequently chosen response option to evaluate the various QoL dimensions was good, while the category poor was used the least. The mean QoL-AD total score of 34.3 is comparable to the reports of other validation studies using the Spanish, Czech, Portuguese, and French self-report scale [26 , 47–49]. The range of 20 points implied a wide variability in the perception of QoL within the sample, which was also revealed in previous investigations [22 , 50].

There is strong evidence that the QoL ratings differ between patients and caregivers, with patients rating their QoL better than caregivers [10 , 51]. Several studies suggest that these differences are related to the presence of anosognosia [17 , 52]. Conde-Sala et al. [17] reported that greater anosognosia was associated with better QoL-AD self-ratings but poorer QoL-AD proxy ratings. Since self- and proxy ratings are influenced by different factors, another explanation for the discrepancy is that the QoL perceptions of patients and caregivers represent two unique and independent points of view. Both perspectives on the patients’ QoL could potentially be valid [13 , 54]. In accordance with these reports, Römhild et al. [27] found an inter-rater gap between the self-rating and proxy rating of the QoL-AD. As both versions cannot be used interchangeably, self- and proxy scores should not be combined. However, the two versions can be analyzed separately to obtain information from both perspectives. Since in our sample all participants with mild to moderate dementia were able to complete the QoL-AD interview, we recommend using the self-report scale for these patients.

For German-speaking patients, the psychometric properties had so far only been confirmed in two other self-report QoL measures: the DQoL [35] and the DEMQOL [55]. Regarding their use in clinical practice, a big advantage of the QoL-AD is its short administration time. Therefore, the QoL-AD can be considered an easy-to-use instrument for the clinical assessment of dementia patients in geriatric hospitals [50].

For the original QoL-AD scale, Logsdon et al. [14] reported a Cronbach’s alpha of 0.88. The internal consistency of the German self-report version (α= 0.79) is similar to the Swedish (α= 0.74 [56]) and Brazilian (α= 0.80 [21]) translations. It can also be considered comparable to the other German self-report scales, since the reported Cronbach’s alpha is similar to that for the DQoL (α= 0.62–0.84 [35]) and the DEMQOL (α= 0.72–0.83 [55]). Regarding test-retest reliability, our results revealed a significantly high correlation between the QoL-AD total scores at time points 1 and 2 (4–7 days apart), indicating good stability for the measure.

The significantly positive correlation between the QoL-AD and DQoL total scores suggests that both instruments measure similar constructs, confirming our first hypothesis on convergent validity. The low to moderate correlations between the QoL-AD total scores and the DQoL subscale scores are comparable to the results of Voigt-Radloff et al. [35] and Wolak-Thierry et al. [50], but not all correlations revealed statistical significance. When interpreting these findings, the conceptual difference between the two measures must be taken into account: The QoL-AD provides a total score and focuses on the perception of interpersonal relationships, environmental factors, and the patient’s own abilities. On the contrary, the DQoL is a profile that evaluates QoL by means of subscales and refers more to the inner states of the patients [22, 50].

We revealed only a low correlation between the QoL-AD self-ratings and the GDS. As we assumed, the correlation was in the negative direction but failed to achieve statistical significance. This finding is surprising, since all of the validation studies using the GDS showed a significant negative correlation (p < 0.01 to p < 0.0001 [13 , 57]). The observed low, non-significant correlation between the QoL-AD and the caregiver-reported neuropsychiatric symptoms did not support our hypotheses but is consistent with validation studies conducted in Portugal [20], Spain [47], and France [49]. In contrast, Novelli et al. [21] and Rosas-Carrasco et al. [32] reported a significant correlation between the QoL-AD self-report scale and the NPI in Brazil and Mexico. Our result may have been influenced by the fact that we did not use the full NPI assessment and therefore did not consider the frequency and severity of neuropsychiatric symptoms. In accordance with other publications [20–22 , 47], we found no correlation between the QoL-AD self-ratings and the MMSE scores, supporting divergent validity.

Strengths and limitations

The strength of the present study lies in the fact that we assessed reliability using two different analysis (test-retest and internal consistency) and evaluated both forms of construct validity (convergent and divergent validity). The selection of instruments was based on previous QoL-AD validation studies to allow a comparison of the German QoL-AD self-report scale with other translations. The main limitation is the small sample size. This may have affected the results, e.g., it could possibly explain the lack of significance in the correlation between QoL-AD and the presence of depressive symptoms. The sample was not selected systematically, which is why the results cannot be generalized. However, in terms of age and cognitive status, our sample is comparable to the larger German sample of the DQoL validation study (n = 287 [35]): The mean age of 77.3 years is identical and there is only a small deviation of 1.1 points in the mean MMSE scores (mean MMSE [35] = 20.8) in both samples. The gender distribution of our participants is comparable to the population of people suffering from dementia in Germany (about two thirds are women [58]). These factors may improve representativeness of the study sample. Another limiting factor is the inclusion of vascular dementia, although the QoL-AD was specifically developed for patients suffering from Alzheimer’s disease. However, this inclusion criterion was also used in previous QoL-AD validation studies in Portugal, the Czech Republic, Italy, Mexico, and Singapore [20 , 59]. Furthermore, we did not include patients with MMSE scores less than 10 and therefore do not provide any information about the suitability of the German self-rating scale in patients suffering from severe dementia. Since a stable retest interval was not compatible with everyday clinical practice, the variability of our test-retest time interval can also be considered a limitation. We did not control the presence of anosognosia in the sample, therefore it should be noted that QoL-AD ratings may have been affected by impaired insight [16, 17].

Conclusion

Our results provide evidence for the internal consistency, test-retest reliability, and construct validity of the German QoL-AD self-report scale. As most of our hypotheses have been confirmed, the translated version can be considered an effective instrument for assessing perceived QoL in German-speaking patients with mild to moderate dementia. Thus, the present study established a basis for implementing the German QoL-AD self-report scale as a valid and reliable QoL measure in research and clinical practice. Future studies should investigate larger sample sizes to substantiate our findings and evaluate the German translation in more advanced stages of the disease.

Footnotes

ACKNOWLEDGMENTS

We like to thank the family members for their support and the participants with dementia who participated in this project.

Authors’ disclosures available online ().

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