 The first index of socio-economic levels occurred in 1994, becoming the standard criteria of classification used in the country.The current index is known as the "Rule 13x6" which classifies into 6 levels the households in Mexico.In 1999 was a protocol called ESIMM (Standard of Service for the Market Research in Mexico) which set the substantive requirements of quality to be observed in any undertaking of research that is operating in Mexico.