I got data from your govt, but the site is non-functioning, so I had to use the wayback machine:
http://web.archive.org/web/20040722025943/http://aspe.hhs.gov/hsp/indicators03/
Specifically,
chapter 2
If this misses out other classes of welfare, I apologise.
It is based on percentage of income received from TANF (or ADFC prior to that), food stamps and SSI. I decided over 75% was a suitable number (because everyone assumes those on welfare don''t work at all). (see the first table under
"Indicator 1. Degree of Dependence" for the 2% total figure).
I got 20% as "long term" from
"Indicator 10. Long-Term Receipt".