Statistics Dictionary

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Blocking is the technique used in a randomized block experiment to sort experimental units into homogeneous groups, called blocks. The goal of blocking is to create blocks such that dependent variable scores are more similar within blocks than across blocks.

For example, consider an experiment designed to test the effect of different teaching methods on academic performance. In this experiment, IQ is a potential nuisance variable. That is, even though the experimenter is primarily interested in the effect of teaching methods, academic performance will also be affected by student IQ.

To control for the unwanted effects of IQ, we might include IQ as a blocking variable in a randomized block experiment. We would assign students to blocks, such that students within the same block have the same (or similar) IQ's. By holding IQ constant within blocks, we can attribute within-block differences in academic performance to differences in teaching methods, rather than to differences in IQ.

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