In a blog post today, Dr. Ronny Kohavi of Bing’s Research & Development team, shares some valuable data about how Bing users interact with search results.

After the 50 percent of users that click the top result, Bing says that only about 4-6 percent click the third result (depending on if it’s an Instant Answer or a regular web page link). Only about 2-3 percent of users click on the fourth result, and so on … down to fewer than one percent click-thru rate on the eighth search result. (Oddly, the graph and blog post completely skip the CTR for the No. 2 search result.)

That trend, Kohavi says, doesn’t apply as much if the searcher clicks his/her back button to go back to the search results page.

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.

That led Bing to start changing how many search results it shows last summer — users would first see eight results, then be shown 12 if they hit the back button. (We wrote about some Bing experiments last summer that offered up to 15-18 search results on Bing.)

By showing extra links after a back button click, Bing says it saw an almost two percent drop in users clicking through to page two.

What’s The CTR on Bing Deep Links?

The post also discusses how searchers interact with a page that includes “deep links” — multiple results from one source grouped together.

Bing says the click-thru rate on the block of results is more than 75 percent — more than three in four searchers click somewhere in the eBay block, for example, as shown below.

When Bing shows deep links like this, the third search result on the page — i.e., whatever shows up two spots below what you see above — gets a CTR of less than one percent.

Bing’s Latest Change: 4 to 14 Results

Based on all of this testing — oh, and the post says that Bing is usually running more than 100 search experiments at any given time — Bing rolled out another change to its search results on Monday: On some queries, it’ll show as few as four search results the first time, and then expand the search results page up to 14 results if you click the back button.

Look at these Bing search results for the query “maaco,” for example. First, the original search:

That’s the whole page of search results.

I clicked on the first result and stayed on MAACO’s home page for about 15 seconds, then clicked my back button and got this:

In this example, I got three results on the first search and 14 after clicking the back button. (I’m not counting the “Related Searches” section that you see on both screenshots; Bing might count it.)

You may also notice that, on the first screenshot, there’s a small link at the bottom offering to let me see more results. Clicking that also brought up a page of 14 search results.

Look for more of this in the future from Bing. “We are now looking at ways to determine whether we should extend the number of search results when we have evidence that users are in exploratory modes (e.g., searching for insurance),” Kohavi writes.