Dementia is a chronic and currently incurable syndrome. Therefore, quality of life (QoL) is a major goal when caring for people with dementia (Gibson et al., 2010) and a major outcome in dementia research (Moniz-Cook et al., 2008). The measurement of QoL, especially proxy-rating, is challenging because of the proxy-perspective (Pickard and Knight, 2005), reliability (Dichter et al., 2016), validity (O'Rourke et al., 2015), and responsiveness (Perales et al., 2013). Probably due to these challenges, it has not been possible to show positive effects for QoL in almost all non-pharmacological interventions for people with dementia (Cooper et al., 2012). One recommended (Moniz-Cook et al., 2008) and frequently used instrument is the Quality of Life in Alzheimer's Disease scale (QoL-AD), which was originally developed in the US for community-dwelling people with dementia. The QoL-AD consists of 13 items based on a 4-point Likert scale ranging from "1"=poor to "4"=excellent (Logsdon et al., 1999). The original instrument has been adapted for people living in nursing homes (NH) by Edelmann et al. (2005).