Planning an experiment in the company of measurement error

"Textbook " calculations of statistical power and/or sample size follow from formulas that as-sume that the variables under consideration are measured without error. However, in the "real world " of behavioral research, errors of measure-ment cannot be neglected. A recent sample-size determination approach is easily adapted to incor-porate unreliability information for both com-pletely randomized and randomized block anal-ysis-of-variance designs. A worked example pre-sents an instance wherein a blocking strategy is clearly advantageous assuming infallible measur-ing instruments, but not when the same instru-ments are granted fallibility. When it comes to designing an experiment,