I think it is more often than other devices at the moment. It would actually depend on the market and fixing certain bugs and the upgrade of new devices on the market. The higher specifications that get manufactured, the better android system it will need, as well as the development of applications and the increase production and need for RAM. They all play a major role in it. I believe that Android would change more frequently than Windows and other certain OS for the smartphone because the more people use them, the more apps will be developed and upgraded, as well as phone manufactured with new system requirements, therefore, more upgrade of Android OS and fixing of bugs that will be suitable for the new devices and the new environment.