1) A sampling method in which units (individuals, households, etc.,) are returned to the sampling frame after use and may be selected for subsequent samples in the same study. 2) An analytic method (also called Resampling or Bootstrapping) in which multiple samples or subsamples are drawn from an existing data set and individuals can be selected more than once in the same sample for analysis. Such samples may be used in statistical analysis to simulate larger samples or distributions.