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ARS Home » Midwest Area » Madison, Wisconsin » U.S. Dairy Forage Research Center » Dairy Forage Research » Research » Publications at this Location » Publication #316371

Title: To block or not to block - what is the impact?

item Casler, Michael

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 12/30/2015
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Proper design of biological experiments involves significant advance thought, attention, and planning of the following items: • A block design should be employed in any circumstance in which the researcher expects some level of spatial or temporal variation among observations. • The most informed choice of a proper block design includes an analysis of the impact of blocking on the F-tests for treatments, including impacts on error degrees of freedom. Blocking robs degrees of freedom from the error or residual term - it carries a cost and the researcher should weigh expected benefits vs. costs. • Blocking can be employed for statistical reasons, logistical reasons, or both. Sometimes the statistical and logistical reasons are at odds with each other, forcing the researcher to make difficult decisions. • Many complex block designs can be collapsed into simpler designs if blocks fail to account for significant variability. Fundamental principles of model fitting in a restricted maximum likelihood format should be used to make informed decisions. • Spatial analyses can be used to augment block designs, but complex block designs can be just as effective, or more so, than spatial analyses. • Retrospective analyses that examine the long-term empirical impacts of blocking for a particular crop-location combination can be highly useful in planning efficient and effective changes to design protocols.