Systematic sampling
（重定向自Systematic sample）
Systematic sampling is a statistical method involving the selection of elements from an ordered sampling frame. The most common form of systematic sampling is an equal-probability method. In this approach, progression through the list is treated circularly, with a return to the top once the end of the list is passed. The sampling starts by selecting an element from the list at random and then every k element in the frame is selected, where k, the sampling interval (sometimes known as the skip): this is calculated as: