PR vs Advertising

Currently writing an essay for Current Issues in Marketing, and I chose the topic why less is spent on PR and more on advertising, hoping that this would include some new topics, that we haven't discussed to pieces. Partly happy with my choice.
I realized that there is no way, in any topic to actually avoid the issue of measurement, which in the industry seem to be the most important factor in keeping business, since the clients always want to make sure that they get a good ROI, including public relation practice.
The problem seems to be that people don't know how to measure eighter advertising or PR, which creates a problem, where the agencies present a whole bunch of stats to the client, trying to justify that the budget spend was indeed a good investment. Clients nod and go of wondering what the numbers actually said.
Luckily enough, for me, in the advertising industry, PR seems to be a lot harder to measure than advertising, which gives advertising at least a few decades on PR as a communication tool. Yippie.
On PR, advertising is at least entertaining to watch, but PR, when you can tell that, which PR practitioners argue that you don't, there is a practitioner and a client behind the news you read or spontaneous outbreaks on the morning show, you just think, how tacky is that. An attempt to sell me something without me noticing. Isn't that much more tacky than advertising that upfront is selling or communicating with you openly, instead of trying to sneak in messages of promotion in what is suppose to be a news story.
Hopefully people recognise the difference.
But okey all PR isn't like that. It is truly interesting to read about new innovations etc.
Martin Trevaskis, editor at Campaign Brief WA, says "Follow the Money".