<http://schema.org/description>
"For marginal cost per lead, I divided the difference in cost over the difference in leads. The difference in cost I found to be $174.75 (using constant CPC and CTR for ad2, and using 10000 impressions for ad2 instead of 15000), and the difference in leads I found to be 13 (100-87).\n\nAdWords won't have this, so if it's something you are looking at, it will take some time to calculate it. Especially if the impressions aren't the same for both ads."^^<http://www.w3.org/2001/XMLSchema#string>
<https://www.pointit.com/blog/ad-copy-testing/>