Participant selection and assignment is vital to experimental design. Define random selection, and explain how it increases the external validity of the research design. Distinguish between a randomized control trial and a match subjects design; explain how both designs increase a study’s internal validity.

Question

What will be an ideal response?

Answer 1

Ans: In random selection, each member of the population has an equal chance of being included in the sample of participants for the study. This procedure increases the likelihood that the results obtained with the sample will generalize to the population, strengthening the study’s external validity. In a randomized control trial, participants are randomly assigned to the experimental and control conditions, equalizing participant characteristics across the groups. This decreases the likelihood that a confounding rather than the independent variable is responsible for any differences in the dependent variable between the experimental and control groups. A match subjects design is used when the independent variable is a participant characteristic, such as the presence of particular disorder. All participant characteristics except the participant variable of interest are held constant across the groups. Like a randomized control trial, this procedure minimizes the likelihood that the results reflect the operation of a confounding variable.