We don't have a pattern, until we drive our population down to 1 million, or we find evidence of an existing or extinguished alien civilization. At the rate we are going, none of these three are going to happen in our lifetime. If only the Vulcan Amish could turn on a radio station... just once every 100 years, in celebration of their Vulcan Amishness... Maybe a pirate Vulcan Amish radio station. You can only hope.