The way search "instances" are defined can be very misleading and make reporting on trends in search data very difficult.
Answer ID 2121 explains how the search metric can be incremented:
- A visitor clicks from a search engine to a page at any time during a visit.
- A visitor refreshes that page after clicking to the page from a search engine.
- A visitor clicks to a page from a search engine, goes to another page within the site, and then clicks the Back button to return to the page.
This means that a single visit can rack up numerous instances of a search phrase if the visitor refreshes the page or comes back to the original page from the search.
Furthermore, this means that at the end of a month (or any reporting period) the number of search instances can be greatly inflated and top searches are likely ranked inaccurately.
There should be a way to "serialize" search instances so that a single visit performing a single search only counts as a single instance of that search phrase.