1. Ad delivered by Targeter T drives Visitor V to your site. Logs indicates V has not been on your site in the last x months - your definition of "new" vs returning visitor. V does not convert on this first visit.

Later, Retargeter R's ad sends V back to your site and V converts. Typically, R gets credit while T gets none, even though T found this valuable visitor in the first place.

Successful retargeting? Or the cumulative effect of advertising, which began with awareness? Do T & R share attribution 50-50? Is R worth 70 to T's 30? Is there any objective way to determine attribution?

2. Retargeter R1 pounds Visitor V with high-frequency ads for 72 hours following first exposure. In addition to being wasteful, this may have negative brand impact on V.

Meanwhile, R2 uses predictive models that account for V being in research vs shopping mode and for a longer conversion cycle for the offer in general.

R1 is racing to win attribution, and the consumer be damned. R2 takes a more scientific approach. If V is ever going to convert, R1 is probably going to win due to sheer volume. If V was in research mode early, however, and R2 keeps testing V's interest over a longer period until V is ready to convert, R2 may yet win, assuming the advertiser hasn't already alienated V with all those early ads!

As you point out, much of this is poorly understood, and you really have to test carefully, one at a time. If you don't, there is too much complexity and so many variables that there can never be a satisfactory solution. With relatively few advertisers all chasing the same cookies, everyone is a "retargeter" and attribution seems impossible.

Good questions ...

(1) Non-biased tactic weighting is all about careful testing. If you do controlled testing then you should be able to weight tactics relative to scale and performance. I know -- very easy to say, harder to do. But it is possible.

(2) Ok, this isn't a contradiction, though I understand how it sounds like one. My point is that, because retargeting could be claiming excess value vs. other tactics, it's excellence might be relatively overstated.

Here's an example: on a particular campaign, you see 5x ROI for retargeting and 2x ROI for tactic X. If you can separate out the retargeting and give all the credit that is due to each tactic, you might learn that retargeting really should be 4.5x ROI, and Tactic X actually delivered 3x. So, retargeting is still the best, just not as much better as you initially thought.