The term quality of life can be identified in Aristotle's classical writings of 330 BC. In his Nichomachian ethics he recognises the multiple relationships between happiness, well-being, "eudemonia" and quality of life. Historically the concept of quality of life has undergone various interpretations. It involves personal experience, perceptions and beliefs, attitudes concerning philosophical, cultural, spiritual, psychological, political, and financial aspects of everyday living. Quality of life has been extensively used both as an outcome and an explanatory factor in relation to human health, in various clinical trials, epidemiologic studies and health interview surveys. Because of the variations in the definition of quality of life, both in theory and in practice, there are also a wide range of procedures that are used to assess quality of life. In this paper several methodological issues regarding the tools used to evaluate quality of life is discussed. In summary, the use of components consisted of large number of classes, as well as the use of specific weights for each scale component, and the low-to-moderate inter-correlation level between the components, is evident from simulated and empirical studies.