In terms of public health, gender is considered one of the main social determinants of health, together with social class and ethnic group . A gender equity measurement tool is important for health policies and public health surveillance at the national level, since gender equity does not constitute a policy area in its own right and thus its implementation falls mainly within the scope of other policy areas such health and social policies. The fact that States base their policies on equity law implies that all Governments support those who have fewer resources. In other words, the principle of fair treatment is applied in order to improve the skills and abilities of all citizens and thus attain a common level of duties so that all benefit from enhanced well-being. The steps that are being taken towards this form of equality are directly linked to the achievement of the health-focused Millennium Development Goals [2–10]. Another, indirect link with health also exists via the achievement of the education-focused goal [11–14].
The Gender Equity Index (GEI) was launched by Social Watch in 2007  and is aimed at helping to promote gender equity and the autonomy of women , which is the third Millennium Development Goal. The GEI has been used both in research  and in grey literature [18, 19], and has attracted much attention from the media . Institutions such as the World Bank or the Global Development Network have used this new index extensively. The GEI ranks the situation of 157 nations with regard to gender equity in education, economic activity (employment) and empowerment (political participation, representation in government positions, law-making).
Other Indexes include the Gender Development Index (GDI), the Gender Gap Index (GGI) and the Gender Inequality Index (GII). The Gender Development Index, created in 1995 by the UN, is a modified version of the Human Development Index which considers women and men separately for life expectancy at birth and for two important determinants of health, education and income . The Gender Gap Index was introduced by the World Economic Forum in 2006 to measure and monitor the magnitude and scope of gender disparities. This index identifies gender gaps in economic development, education, health, survival and political participation .
The Gender Inequality Index, which has been calculated since 2010, shows the loss in human development due to inequality between female and male achievements as regards the dimensions of reproductive health, empowerment and the labour market. Although the GII incorporates empowerment, it also includes a dimension of reproductive health that hinders its association with health variables among women , particularly for those of a fertile age. In addition, while the Gender Development Index and the Gender Gap Index consider life expectancy from birth [21, 22], this has been replaced in the Gender Equity Index by political participation, making it possible to conduct a better statistical analysis of this index relationship to total and cause-specific mortality, as well as to morbidity.
The GEI was designed to identify inequity solely towards women. The way the GEI is formulated has one drawback which impedes its contribution to raising awareness about human rights in that it only reveals inequity towards women and does not consider those situations where women are relatively better off than men, i.e. inequity towards men . As a result, the index is in conflict with the aims for which it was created. GEI values range from 0 (inequity) to 1 (equity). However, in those situations where the percentage of women (numerator) is greater than the percentage of men (denominator), and the value of the ratio is thus greater than unity, Social Watch equals the gap to 1 .
In fact, the greater the denominator with respect to the numerator, the greater the inequity towards women. Furthermore, if the numerator and the denominator coincide, i.e. if the gap is equal to unity, the proportions are maintained and consequently, there is no gender gap, i.e. a situation of equity is reached. However, in those situations where the numerator is greater than the denominator, and therefore the value of the gap is greater than unity (which is possible from an algebraic point of view), Social Watch truncates the result obtained and the value of the gap then equals 1 .
The reason behind this lack of attention is the fact that in the majority of societies it is women who traditionally lose out to men not only as regards rights, professional opportunities and responsibilities, but also in relation to participation in resource management and political decision-making processes. In terms of autonomy and capabilities, it is not merely a case of gender still being a conditioning factor in social design, but rather of it being particularly negative for women (less opportunities in education, professional development, lower participation in the labour market and in politics) [26, 27]. According to M.C. Nussbaum, in statistical terms women are mainly instruments used by others to achieve their own means rather than agents, i.e. subjects capable of fulfilling their own goals in their own name and in their own right [24, 28].
Just as Social Watch developed the GEI to render gender inequities in different countries more visible, in this paper we propose a refined version of the Gender Equity Index that highlights the inequities affecting both women and men, thus generating a more comprehensive measurement of inequity useful in monitoring gender equity for public health surveillance purposes.