**2. Quality of life**

Lyndon Johnson first used the expression quality of life (QoL) in 1964, when he was the president of the United States of America (U.S.A.). He declared: "to evaluate the objectives of a government, the quality of life of the people is better than the balance sheet of the banks" [1]. The originality of this expression was so great that it started to be used in the U.S.A. and soon afterward in Europe in the field of Economics and Sociology when the idea was to study the notion of social welfare in a better way since the economic indicators proved to be insufficient for this purpose.

Although the use of this expression can be considered recent in the history of humanity, some studies claim that the underlying concept is as old as human civilization itself. The idea of life with quality has existed in philosophical references since ancient times.

In Aristotelian thought, for example, the concept of a good life is associated with feeling fulfilled and complete through the practice of virtues. Modern authors see in the course of virtues the roots of the notion of citizenship that we have today [2].

The notion of quality of life (QoL) began to gain meaning in medicine from 1970 onwards, with the observation of an increase in people's life expectancy. If, on one hand, the medical progress has been significant enough to prolong life; on the other hand, it is necessary to ask under what conditions this prolongation takes place. In other words, it is not enough to add years to life but also to add life to years. Therefore, the concept of QoL began to be studied and evaluated [3].

The introduction of the concept of QoL in the health field found other existing constructs. An eminently biological view, such as health status, can support some of these constructs. Others are social and psychological, such as well-being, satisfaction, and happiness. A third group is of economic origin and based on the theory of preference: it presumes the individual's choice when comparing a given health status with another.

QoL presents intersections with several of these concepts. Still, its specificity lies in that it includes other aspects of life and health, such as environment, social relationships, spirituality, and level of independence in everyday life [4].

It is a comprehensive and complex concept since QoL includes health, well-being, self-esteem, and a sense of personal accomplishment from a subjective point of view. From an objective point of view, it has lifestyles, socioeconomic conditions, political aspects, and ideology.

Thus, one can study QoL in healthy populations, where health is just one of the items evaluated. Economic factors or working conditions, rather than lack of fitness, can affect QoL in such people.

Therefore, a first classification of the concept arises:


The World Health Organization's (WHO) definition of health in 1947 clarifies the importance of "a state of physical, psychological, and social well-being" in addition to the absence of disease. Insofar as health goes beyond the absence of disease, the WHO quality of life concept goes beyond the presence of health. It includes an individual's perception of their position in life and considering their goals, expectations, and concerns [1].

It is worth highlighting three fundamental aspects of the quality of life construct, which are:


c.Positive and negative dimensions are necessary to complete the construct. Thus, for a good quality of life, some elements must be present, such as mobility, and others absent, such as pain [4].

#### **2.1 Quality of life assessment**

The quality of life assessment is surrounded by controversies, which start by questioning whether it is possible to measure Q.L. to even discussing the value of the statistical analyses performed.

Randall and Downie summarize their criticism of attempts to measure QoL in five points:


These authors conclude that research on QoL is qualitative and cannot be satisfactorily quantified. Likewise, its results cannot be generalized as in quantitative analysis. They recommend that researchers reflect on why they want to quantify QoL [5].

The World Health Organization, realizing the topic's growing importance in several countries and aware of the methodological difficulties described above, developed the WHOQOL Group (World Health Organization quality of life) in the late 1990s within its Division of Mental Health.

The primary mission of this group was to characterize the concept of QoL and build an instrument for its assessment from a cross-cultural perspective, that is, through an international multicenter study conducted in 15 countries simultaneously.

The WHO introduced the WHOQOL-100, a questionnaire for assessing the quality of life, in 1998.

The increasing use of this questionnaire began to show its advantages and limitations. If, on the one hand, its psychometric properties prove robust, in part due to the number of constant items; on the other hand, it shows limitations due to its extension.

The interest in using QoL measures in population-based and epidemiological studies has prompted the WHO to develop an abbreviated version of that instrument. WHOQOL-BREF has 26 questions and presents a very satisfactory index in the confirmatory analysis of its structure [1]. It assesses the quality of life across four domains: physical health, psychological health, social relationships, and environmental health.
