By contrast, Visual IQ says only 0.6% of its clients' display ad spend have a CPA Skew 70%+ HIGHER than last ad-based CPA. So, according to Visual IQ algorithms at least, an extremely tiny share of display spend is dramatically overvalued.
Meanwhile, in the paid search channel, the difference between low and high CPA skews is not quite as lopsided. Visual IQ says 10.7% of client spend goes to ad placements that have a CPA Skew 70%+ LOWER than "last ad"-based CPA. Compare this to 13.9% of spend on paid search placements that have CPA Skew that’s 70%+ HIGHER than last ad-based CPA.
Muller said, "What this means is that more paid search placements are being overvalued using last ad measurement than are being undervalued – leading to inaccurate optimization decisions – both high and low -- when deciding where to invest future spend. The reason that the CPA Skew for paid search isn’t as great for the display channel is that search is a bottom of the funnel tactic (as opposed to display which is more of a top of funnel tactic).
He adds, "Display is also more of an impression-based tactic, and search is more of a click-based tactic. As a result, search is less disparate in its attributed vs. last ad metrics than display.