Sister shows, also known as companion series, are two or more television series which exist in the same fictional universe and which may have crossovers. They differ to a degree from spin-offs, in that they are established independently from one another. The popularity of most series is limited to a few seasons, and sister shows allow expanding the immediate audience and ratings share. This is accomplished by using mostly different actors and production facilities. Sister shows often shift styles or target audience slightly, for a larger overall market. Thus The Beverly Hillbillies emphasizes slapstick, while Green Acres emphasizes surreal humor.