Who is middle class?

Sorry about this duplication. Will not tweet this link till I add something new.
Just wanted to separate it to remind myself that this is an important topic for a literature review.

However, the figures used by the World Class makes one wonder.... Does the world bank have any idea who are the working poor? These are people earning minimum wages. In France this could be 1365 Euros a month or about 63 Euros a day. Don't tell me these working poor are middle class? If they are lower income class, then middle class must be starting at 70 Euros a day and probably going till 400 Euros a day or 90000 Euros a month.
In India, I doubt that people will consider their maids as middle class. Their driver perhaps. So, if a full time maid is earning about Rs 3000 a month, or Rs 100 a day or $ 2 (probably $ 5 in ppp terms), then this cannot be middle class. Middle class is probably $ 4 or $ 10 in ppp terms per day. On the high end, someone earning Rs 1 lakhs a month no longer believes he's made it to the upper class. This is about Rs 4000 per day or $100 a day (more in ppp).
So, I guess we need to write our own history based as much on sociology as economic statistics.