TheOptimizationIdiot - 7:15 am on Mar 18, 2013 (gmt 0) [edited by: TheOptimizationIdiot at 7:18 am (utc) on Mar 18, 2013]
The only real variable is whether a user opens more than one page without reloading the search-results page.
Not really. If the user opens Page A and clicks on Page B 1 second later when their average click time between two results is 5 seconds it tells you something different than if they open Page A and don't click on Page B for 17 seconds when their average click time between results is 8 seconds.
Sure, you'll miss some when then phone rings or something on a specific result set, but if there's a difference in click time between a specific result and the average click time between different results exhibited by a given user it definitely tells you something.
And without getting into too much detail, the click time between results could indicate a better or worse answer, depending on the click time behavior of other visitors to the result set and the specific visitor within other result sets.
For example, if the click time is higher between results for a specific result, but 90% of the time the search does not end when it ends an average of 20% of the time on 3 other results, it can tell you the "longer click time" is due to some "non-informative distraction" by the site with the longer visit time making it a worse result, but if the result with the longer visit time has a higher than average "search ends" % than the rest say it's 35% and the next closest average is 20% for 3 other results it can tell you the result is generally better than the rest.
Click time between results on average for users is in my opinion a very important metric and it's really tough to fake.
[edited by: TheOptimizationIdiot at 7:18 am (utc) on Mar 18, 2013]