Thanks for your interest in the National Journal vote ratings.
As described in this linked piece, the ratings are not based on an outside group or individual's standard of what is the "conservative" or "liberal" position on a set of issues. They are based on how the 435 House members (and, separately, the 100 Senators) lined up ideologically relative to each other. http://hotlineoncall.nationaljournal.com/archives/2010/02/ma... By that measure, there were more consistent conservatives in the House than Rep. Paul.
This is how we have prepared our vote ratings for nearly 30 years.
There are, of course, other ways to measure ideological performance and other groups that weigh it.
Ron Paul's Convention Speech