Single

According to a new report from the Carsey Institute, a public policy think tank at the University of New Hampshire, working wives contributed 47% of total family earnings in 2009, a 2% jump over the year before and the largest single increase in the last 15 years.

here is the full text.

http://news.yahoo.com/s/time/httphealthlandtimecom20101007morefamiliesrelyonworkingwifexidrssfullhealthsciyahoo

My question is that I think 'the largest single increase' equals 'the single largest increase' ,which actually equals ' the largest increase', 'single' here is just for emphasis.

here is what I found in dictionary :

the single biggest/greatest etc
used to emphasize that you are talking about the one thing that is the biggest, greatest etc.

but someone else explains it as 'the largest single increase = the largest percentage increase in a single year' ,which confused me.

I would like you give me an accurate explanation.

Thank you!