Measurement of the middle class

OCDE defines the middle class as those households where per person expenditure range is between $10 and $100 per day. The organization hopes tha by 2030 this population group will reach 4900 million people, multiplying the size of 2009 by 2.6. However, two important "buts" are presented. First, that this growth will focus almost exclusively on Asia and Latin America, highlighting especially the emerging Chinese middle class, while in the "old" Europe, United States and other developed countries, the middle class seems to be entering in a recession. Second, that this definition of medium classmay be inadequate or questionable to measure the social economic phenomenon in different world palces or situations. It seems so of great interest more deeper studies about the demography of the middle class in cross-section and dynamic manner in different countries affected by the changes that have been cited. Our research -of which this paper is first output- aims to develop a methodology to quantify the middle class, robust to different expenditure patterns in different societies and a comparison between them that allows us to determine the importance of demographic changes of this social class in Spain, using the methodology of the multidimensional cluster, for what a few previous steps -main components, conventional cluster analysis- should be done. Performed the previous steps, in this first part of the study, interesting conclusions have been obtained. Four factors have been found with regard to the part of main components and sets the hypothesis, for one of them, of their relationship with the structures of expenditure according to the cycle of life of households. In terms of conventional cluster analysis, this leads us to say that four types of households can differentiate while two of them would be related, except for the variable age, and they include the possible "middle class" and that traditional cluster analysis is not suficient to discriminate it. Thus we also extract a methodological conclusion and it is the use of the methodology of multivariate cluster appears as a necessary step to complete the study.