In practice, stand density indices must be estimated from sample data, leading to uncertainty in both estimates of stand density and resulting thinning decisions. We provide a statistical framework for thinning decisions based on density thresholds. We show how to assess the adequacy of existing cruise data to guide the thinning process, and to design more cost-effective sampling plans. We present this information in a series of graphs which, when used in conjunction with density management diagrams, can improve rational thinning decisions. West. J. Appl. For. 12(3):89-92.