True... I found out that the party membership in Sweden is at about 7 percent of the total adult population. Or at least it was 5 years ago. So the numbers somewhat match, I guess. I am not so sure if that means they will actually manage 4 percent of the vote nation wide, but if the Swedish parliamentary system is as close to the Norwegian as I think it is, they should at least have a big chance of picking up seats in the bigger cities and counties.

(source (in swedish): http://www.scb.se/statistik/LE/LE0101/1990I99/LE100SA0301_08.pdf)