Ageing is a socio-economic product. A large part of the variability in the degree of ageing is explained by a broad social and economic class discrepancy emerging from the multiple sectors that compose its society. Ageing, particularly in the developing countries, has a considerable variance with regard to its initiation, appearance, development and consequences in its different biological, socio-economic and psychological manifestations. By reason of the variability in the economic and psychological, social and biological, formal and informal, pragmatic and legal determinants of ageing, we recognise the inaccuracy in determining a chronological age at which one is considered to have arrived at that last stage of life. Many other issues arise which hinder us from effectively exploiting the rich benefits which can be derived from comparative cross-national research.
International research is plagued by a myriad of variations.
This implies our ability not only to measure the health and well-being but also to accurately define the presence or absence of impairment or disability. It is precisely here that several doubts are expressed as to the possibility and quality of such attempts made at international comparative studies. Furthermore, although we often speak of functionality in old age, we still lack a universally accepted composite measure of functionality, resulting in innumerable variations in such areas as activities of daily living, general activities' scales, general health status, physical performance measures, etc. The complexity of the issues at hand is further pronounced due to the fact that the research studies on ageing have not only multiplied, but their scope has also broadened to include many disciplines and age-related phenomena. These studies examine the various aspects of ageing from basic biomedical, biological, behavioural, demographic, economic, environmental and social perspectives.