capitalist class relations;" the Ehrenreichs named this group the "professional-managerial class". This group of middle-class professionals is distinguished from other social classes by their training and education (typically business qualifications and university degrees), with example occupations including academics and teachers, social workers, engineers, accountants, managers, nurses, and middle-level administrators. The Ehrenreichs developed their definition from studies by André Gorz, Serge Mallet, and others, of a "new working class," which, despite education and a perception of themselves as middle class, were part of the working class because they did not own the means of production, and were wage earners paid to produce a piece of capital. The professional-managerial class seeks higher rank status and salary and tend to have incomes above the average for their country. Recent global growth It is important to understand that modern definitions of the term "middle class" are often politically motivated and vary according to the exigencies of political purpose which they were conceived to serve in the first place as well as due to the multiplicity of more- or less-scientific methods used to measure and compare "wealth" between modern advanced industrial states (where poverty is relatively low and the distribution of wealth more egalitarian in a relative sense) and in developing countries (where poverty and a profoundly unequal distribution of wealth crush the vast majority of the population). Many of these methods of comparison have been harshly criticised; for example, economist Thomas Piketty, in his book Capital in the Twenty-First Century, describes one of the most commonly used comparative measures of wealth across the globe – the Gini coefficient – as being an example of "synthetic indices ... which mix very different things, such as inequality with respect to labor and capital, so that it is impossible to distinguish clearly among the multiple dimensions of inequality and the various mechanisms at work." In February 2009, The Economist asserted that over half the world's population now belongs to the middle class, as a result of rapid growth in emerging countries. It characterized the middle class as having a reasonable amount of discretionary income, so that they do not live from hand-to-mouth as the poor do, and defined it as beginning at the point where people have roughly a third of their income left for discretionary spending after paying for basic food and shelter. This allows people to buy consumer goods, improve their health care, and provide