Random assignment defines the assignment of participants of a study to their respective group strictly by chance.
Statistical inference is based on the theory of probability, and effects investigated in psychological studies are defined by measures that are treated as random variables. The inference about the probability of a given result with regard to an assumed population and the popular term “significance” are only meaningful and without bias if the measure of interest is really a random variable. To achieve the creation of a random variable in form of a measure derived from a sample of participants, these participants have to be randomly drawn. In an experimental study involving different groups of participants, these participants have to additionally be randomly assigned to one of the groups.
Why Is Random Assignment Crucial for Statistical Inference?
Many psychological investigations, such as clinical treatment studies or neuropsychological training...