Starting from early December 2015, some of Google’s result pages started showing 4 sponsored results (as opposed to 3 results thus far).
In the beginning of December about 1% of search results was affected. This experiment is not restricted to the USA, appearances of 4 sponsored results had been noted in Israel and Germany as well.
This is bad news for SEOs – Google is pushing organic results a little further down the SERPs, and slightly lowering their relevancy. This is also a harsh blow to website owners (beyond the organic issues) – if a competitor advertises using the brand name of a certain website owner, that website might find itself ‘below the fold’ whereas sponsored results would appear above it.
If you’ve experienced a decrease in your website’s traffic during December and haven’t seen any changes in ranking, this update could be the cause since it pushes down organic results, which leads to a lower CTR.