[danso]

I don't have much experience with the lobbying rules except for times that I've had to research things specifically. Usually disclosure requirements come with a minimum amount...In the House (not sure if the exact limits apply to the Senate...), the ethics rules are quite strict but not everything is recorded...for example, a legislator (or their staff) can only receive $100 of gifts from a single source in a calendar year..."gifts" being basically anything of value...but things under $10 don't count toward that limit. So getting Frappuccinos everyday with your favorite CEO probably wouldn't be recorded in any official capacity even though not only do those add up monetarily, but someone getting coffee with a legislator on a frequent basis would be a huge point of potential influence. However, legislators aren't allowed to get gifts (such as paid dinners) at all from a registered lobbyist [1].

Both the House and the Senate have gift travel databases (travel that's reimbursed by an outside group, such as a charter flight to visit an oil drilling rig) [2]

The branches differ in how such things are reported...this was pretty obvious recently when Justice Scalia died at a ranch and people started wondering who paid for the trip...take one look at how these forms are supplied and it should be pretty obvious why we don't normally hear about SCOTUS relationships until something really weird happens [3].

This NYT editorial "So Who's a Lobbyist?" has a nice rundown of the ways that people who would generally be considered a lobbyist can escape disclosure requirements: http://www.nytimes.com/2012/01/27/opinion/so-whos-a-lobbyist...

Still, it's useful to be able to parse the dataset in an attempt to find what's missing...something that is difficult to do conceptually unless you're dealing with the actual dataset on your own system.

[1] https://ethics.house.gov/gifts/house-gift-rule

[2] http://clerk.house.gov/public_disc/giftTravel.aspx

[3] http://pfds.opensecrets.org/N99999918_2008.pdf