I think the definition of each of the "classes" would be the way income is broken down into quintiles (fifths).I think you are correct Independent. Almost everyone "thinks" they are middle class. However depending upon which definition you look at, the limits for what "middle class" is and is not, are wildly conflicting. I saw one chart that showed anyone making over 70k / yr is considered upper class. Others say over 100k. Why do so many people get the idea that somehow people that make more money than they do, are "taking" that money away from them? That is the "thinking" behind highly compensated earners not being allowed to save more. It is somehow believed that if we were all more "equal" then everything would be ok.... complete craziness....
Lower class = first quintile
lower middle class = second quintile
middle class = third quintile
upper middle class fourth quintile
uppler class = fifth quintile
According to the census bureau that breaks down like this for 2006. (Historical Income Tables - Households)
Lower = less than $20,035
lower middle = $20,035 to $37,774
middle = $37,774 to $60,000
upper middle = $60,000 to $97,032
upper = greater than $97,032
Further breakdowns by race are here: Historical Income Inequality Tables