The main goal of caring for people with dementia is the maintenance and promotion of their quality of life (Qol) . Qol has become an important concept as an outcome in intervention studies, particularly psychosocial interventions, as well as an indicator of the quality of care of people with dementia [2–5]. The World Health Organization defines Qol as “individuals’ perceptions 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” . One early and highly recognized model describes dementia-specific Qol consisting of objective (e.g., behavioral competence and environment) and subjective (e.g., perceived Qol and psychological well-being) components (called ‘sectors’ by Lawton) [7, 8]. Based on this theoretical approach, Jonker et al. developed a hierarchical model that defines psychological wellbeing as the starting point and central indicator for dementia-specific Qol . Those authors argue for the consideration of non-dementia-related domains of Qol, such as personal factors (e.g., religion, income, age), next to environmental characteristics and dementia related domain.
In 2005, Ettema et al. defined the Qol of people with dementia based on a literature review that specified dementia-specific Qol as ‘the multidimensional evaluation of the person-environment system of the individual, in terms of adaption to the perceived consequences of the dementia’ . Based on this definition, the seven adaptive tasks of the adaption coping model were interpreted as dementia-specific Qol domains: 
dealing with own disability, developing an adequate care relationship with the staff, preserving an emotional balance, preserving a positive self-image, preparing for an uncertain future, developing and maintaining social relationships and dealing with the nursing home environment
. This model highlights the importance of psychosocial domains, which is supported by a recent review which showed 10 psychosocial (e.g., attachment, social contact, spirituality) as well as 3 physical and practical domains (e.g., physical health, financial situation) of Qol judged by people with dementia . During the course of the theoretical developments, several dementia-specific Qol instruments have been developed, using self-ratings, proxy-ratings or direct observations as the data sources [14, 15].
The majority of these instruments have been developed in English-speaking countries (particularly the USA and the UK). In Germany, Qol has recently been characterized as a nursing outcome by the medical service of the statutory long-term care insurance program. . Only one German Qol instrument has been developed to date: the Heidelberg instrument for the assessment of quality of life in dementia (H.I.L.D.E.) . This instrument is not typically applicable in research studies because it is moderately time-consuming (> 30 min per resident). A recent review did not identify any Qol instrument for people with dementia that has been validated in Germany . To the best of our knowledge, there are a limited number of Qol instruments that have been translated into German, including the Qol-AD , D-Qol [20, 21] and QUALIDEM . These instruments have not been fully psychometrically tested. With the exception of the QUALIDEM, these instruments do not sufficiently focus on the Qol domains that are judged important for people with dementia .
The QUALIDEM has been evaluated in terms of psychometric properties with a focus on the psychosocial domains of dementia-specific Qol . The instrument is simple to administer  and was developed for proxy-rating of Qol throughout the entire course of dementia in nursing home residents . Consequently, the use of the QUALIDEM is recommended for Qol assessment in the late stage of disease  and for longitudinal ratings . Its focus on psychosocial domains allows the instrument to assess several important Qol domains (affect, attachment, self-image, being useful, social contact, sense of aesthetics in the living environment, security and privacy, self-determination and freedom) that were described in an earlier review  and judged as important by people with dementia.
was developed and validated between 2005 and 2007 in the Netherlands. It consists of two consecutive versions for people with mild to severe and very severe dementia. The stages of dementia severity are classified according to the Reisberg scale, the Global Deterioration Scale (GDS) and Functional Assessment Staging (FAST), the last of which ranges from 1 (no cognitive impairment) to 7 points (very severe dementia) [27
The Qol of people with mild to severe dementia (FAST = 2–6) is assessed by the 37-item version covering nine domains: care relationship, positive affect, negative affect, restless tense behavior, positive self-image, social relation, social isolation, feeling at home and having something to do.
The domains positive self-image, feeling at home and having something to do cannot be assessed in people with very severe dementia (FAST = 7). The second version of the QUALIDEM comprises 18 items covering six domains of Qol: care relationship, positive affect, negative affect, restless tense behavior, social relation and social isolation.
The response options for all items are “never”, “rarely”, “sometimes” and “frequently”. In 2008, the QUALIDEM was translated to German by a certified agency using forward-backward translation. The back-translated version was verified by the questionnaire’s first author, whose comments were taken into account for the adaption of the German version. In an exploratory investigation, the German QUALIDEM indicates construct validity measured by factor analysis and moderate to high internal consistency .
This paper outlines the evaluation of scalability (construct validity) and internal consistency of the German QUALIDEM, based on a large sample. The study followed a confirmatory methodological approach that has been used successfully by other studies in The Netherlands [12, 26]. Additionally, the distribution of the subscales scores as differentiated by the subgroups of dementia severity, age and gender will be presented.