The bottom third of net compensation in 2011 went to 112 million earners who comprise the first 74% of all earners. Altogether they earned $2.2 trillion of the $6.24 trillion of total net compensation for the year.
You remain in this group until you earn somewhere between $45,000 and $50,000 a year, after which you may be said to join those earning the middle third of net compensation.