Statistics Dictionary

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Blocking Variable

In a randomized block experiment, a good blocking variable has four distinguishing characteristics:

  • It is included as a factor in the experiment.
  • It is not of primary interest to the experimenter.
  • It affects the dependent variable.
  • It is unrelated to independent variables in the experiment.

A blocking variable is a potential nuisance variable - a source of undesired variation in the dependent variable. By explicitly including a blocking variable in an experiment, the experimenter can tease out nuisance effects and more clearly test treatment effects of interest.

Warning: If a blocking variable does not affect the dependent variable or if it is strongly related to an independent variable, a randomized block design may not be the best choice. Other designs may be more efficient.

See also:  Randomized Block Designs | Randomized Block Experiments: Data Analysis