Omega-3, finis Exercises 21 and 23 describe an experiment...

Omega-3, finis Exercises 21 and 23 describe an experiment investigating the effectiveness of omega-3 fats in treating bipolar disorder. Suppose some of the 30 subjects were very active people who walked a lot or got vigorous exercise several times a week, while others tended to be more sedentary, working office jobs and watching a lot of TV. Why might researchers choose to block the subjects by activity level before randomly assigning them to the omega-3 and placebo groups?

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Key Concepts

Random Assignment within Blocks

Random assignment is crucial in experimental design to ensure that participants are allocated to treatment groups without bias. When randomization is performed within blocks, it further balances the distribution of the blocking variable (activity level) across the treatment groups, increasing the internal validity of the study by ensuring comparable groups.

Confounding Variables

Confounding variables are factors other than the independent variable that could affect the outcome of the experiment. In this context, varying levels of physical activity might influence the results, so grouping participants by their activity level before randomizing them helps minimize the confounding effects, allowing researchers to attribute differences in outcomes more confidently to the treatment.

Blocking

Blocking is an experimental design technique where participants are grouped into subsets (blocks) based on specific characteristics that are thought to influence the outcome. By doing so, the researcher can control for the variability introduced by these characteristics, ensuring more accurate comparisons between treatment groups within each block.

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