Rep. Paul Ryan got an immediate ratings boost after his selection as Mitt Romney's running mate, according to a new Washington Post-ABC News poll.

Ryan was not well known nationally before Saturday's announcement, and favorable impressions of him jumped 15 percentage points among the overall electorate, with positive views soaring from 49 to 70 percent among conservative Republicans.

In interviews conducted Wednesday through Friday, 45 percent of Americans expressed no opinion of the congressman from Wisconsin. That number dropped to 30 percent after the news was announced. The increasing familiarity all went to the positive side of the ledger.

Overall, in interviews after his selection, 38 percent of all Americans expressed favorable views of Ryan, while 33 percent had negative ones. Before the announcement, he was somewhat underwater, scoring 23 percent favorable and 32 percent unfavorable.