Adam, Brigitte, et al. “Elderly Single-Family Homes in Transition. A Cluster Analysis to Identify Regional Challenges in North Rhine-Westphalia”. Raumforschung Und Raumordnung | Spatial Research and Planning, vol. 76, no. 1, Feb. 2018, pp. 3-17, https://doi.org/10.1007/s13147-017-0479-y.