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Stat Med. 1990 Dec;9(12):1455-62.

Testing for imbalance of covariates in controlled experiments.

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Department of Epidemiology and Preventive Medicine, University of Maryland School of Medicine, Baltimore 21201.


Results of a controlled experiment are often adjusted for covariates found by a preliminary test to differ significantly between the treatment and control groups. The resulting test's true significance level is lower than the nominal level. Greater power can be achieved by always adjusting for a covariate that is highly correlated with the response regardless of its distribution between groups.

[Indexed for MEDLINE]

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