In several parts I have read that a criterion is relatively useful to define the nebulous middle class is simply using a criterion focused on the median: A group that has an income defined as a percentage of the median (let’s say between 75% and 125% of the median income, which as mentioned Barozet and Espinoza is the international standard). It seems a clear way of referring to what that should indicate the term middle class: Those who are in the middle of the segmentation socio-demographic characteristics.
Unfortunately does not have much sense. The middle class is not defined by who is in the middle, but because this is in between: Because they have the sectors ‘up’ and ‘down’. In other words, the concept is purely relational. The important thing of the middle class is that, finally, does not belong to the elite nor to the poor (or to the popular sectors to the workers or to any way in which a society defines its lower sectors). This belonging is something that actually occurs in social processes, and something recognized in the society. Is a specific location, and recognized in the social structure, not just a place on a scale statistic. It has to do with those who are recognized as equals, as peers; and those who are not recognized as such.
Why is it important? Because it reminds us that the ‘bottom’ in various societies have been the great majority of the population. In a society organized by aristocrats / burghers / peasants, the peasants are more than half of the population and that does not mean that the ‘middle class’ are the bourgeois (even if by a criterion of revenue were not clearly above the median). The important thing was that clearly the burgesses were not farmers (they had the same standard of living, nor the same expectations and any interaction between them would be clear who was superior and who inferior), nor part of the elite (for the same reasons).
To define the middle class according to the median us seems relatively reasonable now, but that is due to specific characteristics of our societies (the difficulty of delimiting segments in societies formally based on equality of rights, in that levels of income are continuous and without jumps etc) But as a general statement, makes us forget the phenomenon of which we are speaking.