Should blocks be fixed or random?

Date
2016-01-01
Authors
Dixon, Philip
Dixon, Philip
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Altmetrics
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Statistics
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Statistics
Abstract

Many studies include some form of blocking in the study design. Block effects are rarely of intrinsic interest; instead they are included in a model so that that model reflects the study design. I consider the question of how these block effects should be modeled: as fixed effects or as random effects. I discuss the consequences of the choice, including the recovery of inter-block information when available, give a simple example to illustrate the connection between recovery of inter-block information and pooling two estimators of a treatment effect, and give an example where fitting a model with random block effects can lead to the wrong answer. I suggest that block effects should be modeled as fixed effects unless there are compelling reasons to do otherwise.

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This proceeding is from Dixon, P.M. Should blocks be fixed or random? 2016 Conference on Applied Statistics in Agriculture Proceedings, May 1-3, Manhattan Kansas. Kansas State University. doi: 10.4148/2475-7772.1474.

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