It could be a typo or other mistake. To be clear, "medium income" was the phrase used by Philip Longman in the cited PDF. I also wonder if he actually meant "me

It could be a typo or other mistake. To be clear, "medium income" was the phrase used by Philip Longman in the cited PDF. I also wonder if he actually meant "median income." I googled on "define medium income", and it seems P.L. isn't alone in using that term, but it's not clear to me if it's taken the same as median, or if it's a unique term all its own. In the book, "Children in America: National Indicator of Well-being", edited by Ryan H. Nobbins, in Appendix A (page 121), "medium income" is given a definition (see https://books.google.com/books?id=ALccZ2yFq9UC&pg=PA121&lpg=PA121&dq=define+medium+income&source=bl&ots=WKBXiHsEgU&sig=1NqUR_0MjpIJ1X_QuSRqHSClLSc&hl=en&sa=X&ei=xf6aVJucFMGigwTYnYCIDQ&ved=0CEQQ6AEwBg#v=onepage&q=define%20medium%20income&f=false https://books.google.com/books?id=ALccZ2yFq9UC&pg=PA121&lpg=...), although I don't know if P.L. means it this way: Medium Income is between 200 and 399 percent of the poverty threshold (e.g. from $37620 thru $75239 for a family of 4 in 2003).