Researchers must grapple with many sources of potential bias and contamination in their research, including the Hawthorne effect, the John Henry effect, and expectancy threats (also known as the Pygmalion effect or self-fulfilling prophecy); the threats of extraneous events, instrumentation, mortality, regression, and selection; order effects; and spurious relationships

Researchers must grapple with many sources of potential bias and contamination in their research, including the Hawthorne effect, the John Henry effect, and expectancy threats (also known as the Pygmalion effect or self-fulfilling prophecy); the threats of extraneous events, instrumentation, mortality, regression, and selection; order effects; and spurious relationships. Possible solutions to these problems (and related ones) include blinding, placebo groups, randomized control groups, counterbalancing, and the use of partialing in statistical analysis. Use an Internet search engine such as Google and key in a term such as “sleep learning,” “learn faster,” “better memory,” or another similar desire related to learning. Be highly skeptical as you sort through the results. Find an especially doubtful claim, one that offers “proof” with a “scientific study.” Carefully examine the research evidence. Try to identify one of the problems in the list above that would invalidate the evidence. Then describe how one of the control techniques could be used in a redesign of the study to control the problem you identified.