Webtrends Analytics 9 Adminstration Guide, November 2012
If you use Webtrends query parameters to track referrals from search engines, you can use Visitor History to determine which search engines and phrases visitors use most to find your site. You can also evaluate the effectiveness of both paid and organic searches.
Because you can specify how many recent searches to track for each visitor, only the most relevant visitor data is included in search-related reports.
As a best practice, you should only use visitor history-generated search engine dimensions with hit-based measures. If you include measures that are visit-based, reports might include duplicate counts if a visitor performed multiple searches during the same visit. When creating a two-dimensional report, make sure both dimensions are visitor history-generated search engine dimensions.
Do not include visitor-related measures in these reports.