My colleague, PR prof and guru Karen Russell, will love this -- evidence that good PR matters. According to this study, higher quality press releases from medical journals result in higher quality news stories. Information subsidies, confirmed.
I can also stretch this to what people know, of course, by pointing out the following causal connection:
Quality PR --> Quality News --> Better Learning about Medical News
They don't test this, unfortunately, but I'm confident in the causal relationship.