There's an old saying: "Half of advertising is wasted -- it's just that nobody knows which half."
It's hard enough to figure this out when you're talking about advertising and marketing, when at least you can measure things directly through sales.
When you're selling a product, experiments are possible. You can run one ad campaign in the Cleveland media market and try something else in Denver, then compare your sales in those two markets.
You can't do that with public relations.
First, there's no way to guarantee the same media coverage in two different markets. Not when you're relying on public service announcements and earned media.
Second, you're not selling of widgets. There's no direct outcome to measure.
Yet there are things to learn from new thinking on what works and what doesn't.
Rex Briggs and Greg Stuart point out in their book, What Sticks, that we do know some things, and that science and hard numbers are much more effective than anecdotes and tradition.
Briggs and Stuart point out that if an audience gets the same message in three different places -- in the newspaper, on the radio and on TV -- it's much more effective than having that message repeated three times in the same medium.
Other studies show that you don't have to change the messenger. Having the same messenger say a thing three times is just as effective as having three different people say the same thing.