  In many situations, the decision maker observes items in sequence and needs to determine whether or not to retain a particular item immediately after it is observed. Any decision rule creates a set of items that are selected. We consider situations where the available information is the rank of a present observation relative to its predecessors. Certain ``natural'' selection rules are investigated. Theoretical results are presented pertaining to the evolution of the number of items selected, measures of their quality and the time it would take to amass a group of a given size. 
Select sets: Rank and file