What does the term 'block design' refer to in experimental design?

The term 'block design' in experimental design specifically refers to a method that aims to minimize the effects of nuisance variables by grouping similar experimental units into blocks. This technique allows researchers to control for those nuisance variables by ensuring that they are evenly distributed across the treatment groups. By doing so, any variation in outcomes can be more confidently attributed to the treatments being tested rather than extraneous influences.

Implementing block design can enhance the precision of the experiment, as it helps isolate the treatment effect from variabilities that could confuse the results. For instance, if a study is examining the effects of a new medication on blood pressure and the subjects vary significantly in age, blocking by age groups enables a clearer understanding of how the medication performs across those different age blocks while controlling for age-related differences.

This method of grouping contrasts with other potential experimental designs where either no such control is applied, such as in the case of designs that do not account for nuisance variables, or where random sampling methods are employed without stratification, potentially leading to confounding results. The deliberate arrangement of subjects into blocks is fundamental in improving the overall validity and reliability of the experimental findings.