By taking advantage of remarketing networks as an advertiser, you can display your banners on other sites to visitors who have previously visited your site without converting.
Measuring the effectiveness of remarketing (also known as “retargeting”) in boosting return conversions poses a special challenge, for these two reasons:
• The overwhelming majority of the return conversions for which the remarketing network credits itself are “viewthrough” conversions, that is, conversions that occurred after a visitor was exposed to at least one impression of your banner and then returned to your site not by clicking the banner but through another means, such as a direct visit, sometime after the banner impression.
• Some of those return conversions would have undoubtedly occurred even if you were not doing any remarketing.
So how can we use Google Analytics to supplement the reports provided by the remarketing networks?
Apply the Return Visitors advanced segment to the Goals > Overview report.
A significant increase in return-visit conversions relative to new-visit conversions could mean that the remarketing campaign is having an impact.
Check the Multi-Channel Funnels > Time Lag report.
A shorter average time lag might indicate that the banner ads are expediting return conversions, while a significantly longer time lag might signal that the banners are prompting return conversions that would not have otherwise occurred at all.
Include campaign parameters in inbound links.
To track the percentage of conversions that do result from actual clickthroughs, campaign parameters on inbound links are a must, especially since the banners will appear on potentially hundreds or even thousands of sites, thus eliminating any reasonable possibility of tracking by referrer.
Also keep in mind that if you participate as an advertiser in more than one remarketing network, each will likely take credit for some of the same conversions (because of the viewthrough ambiguity).