1. Acsády J, Kucsera C, Széman Z (2004) ENABLE-AGE survey study T1: national report Hungary. Project QLRT-2001-0, delivered to the European Commission. Institute of Sociology, Hungarian Academy of Sciences, Budapest
2. Baltes PB, Smith J (1999) Multilevel and systemic analyses of old age: theoretical and empirical evidence for a fourth age. In: Bengtson VL, Schaie KW (eds) Handbook of theories of aging. Springer, Berlin Heidelberg New York, pp 153?173
3. Brandt Å, Iwarsson S, Ståhl A (2004) Older people?s use of powered wheelchairs for activity and participation. J Rehabil Med 36:70?77
4. Charmaz K (1996) Grounded theory. In: Smith JA (ed) Rethinking methods in psychology. Sage, London, pp 27?49
5. Charmaz K (2003) Grounded theory. In: Smith JA (ed) Qualitative psychology. A practical guide to research methods. Sage, London, pp 81?110