After some experimenting and monitoring user behavior, Bing has made some changes to the way its shows search results.

Bing R&D Partner Architect Dr. Ronny Kohavi discussed Bing’s testing and findings in a blog post. Much of the findings seem pretty obvious. Clickthrough rates go down for results that are lower on the page, for example. Things get a little more interesting when users hit the back button, however, and this has influenced Bing’s strategy for showing results.

“On average, over 50% of users click on the first result on the page,” Kohavi writes. “From there we see a significant drop, with less than 1% of people clicking on the 8th link on the page. The figure below shows the click-through rate dropping from position 3 on, where position 3 could contain an Instant Answer, or the 2ndweb result that was pushed down because there was an Instant Answer above it, etc.”

“With this insight in mind, we looked for interesting cases where the click-through rate is much higher on lower results,” continues Kohavi. “One interesting case was after a user hits the back button. When users click on a result, then hit the browser back button, they typically look lower on the page. Statistics showed that the click-through rate on lower positions are a factor of five to eight times higher after a back button. This observation led to a change to Bing in the US in late May 2012 so that the SERP initially showed eight algorithmic results, and the page was extended to 12 after a back button. The controlled experiments showed that key metrics improved: users were executing fewer queries per session, pages rendered faster on average, and pagination to page 2, 3, etc. reduced by almost 2%.”

Now Bing is truncating search results pages more aggressively, showing just the first four elements (which can be either algorithmic results or instant answers), as well as as news results when relevant, and is extending the SERPs after the back button is pushed to 14 algorithmic results. According to Kohavi, this leads to more successful sessions for users, people finding what they’re looking for more quickly, a decline in queries per session, pages rendered faster (on average), and a 5% reduction in pagination.

The changes were pushed to all Bing users earlier this week (April 22nd, to be exact).