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Researchers use experimental design to create the framework of an experiment. Hypotheses can be tested using one or multiple designs. The design is impacted by what is being tested and consists of the number of treatment conditions that show if the subjects will be the same or a different individual in all conditions. Three aspects of an experiment will determine what design is used; therefore, the experimenter must determine the number of independent variables; treatment conditions for fair testing; and the type of subjects to be used in each of the treatment conditions (Myers & Hansen et al., 2012).
Between-Subjects design consists of at least one control group, and one experimental group, or several groups that are different on a variable. This way, all experimental group receives an independent variable treatment that should have bearing on the results, and the group that is controlled gets either no treatment, a dummy treatment, or a treatment completely unrelated. Then a comparison is made with the dependent variable measures between groups to verify if the manipulation of the independent variable was effective. When there is a notable difference, the researcher can conclude that the effect was caused from the manipulation of the independent variable.
Between-subject designs can also be classified as independent measures or independent group designs because researchers can compare measurements not relating to the experiment. This method of design is used mostly when researchers want to be able to compare two or more treatment conditions using diverse groups of individuals for each treatment or level of independent variables (Bhandari et al., 2021).
Example: To assess if a new infant formula containing molasses (independent variable) will cause infants to start walking between four and six months old (Dependent variable), we design a longitudinal study where we gather a sample size of 10 parents with newborns. Then use between-subjects design to divide them in two distinct groups, a control group where the participants are fed a formula without molasses, and the experimental group that are fed with the new formula consisting of molasses. Then collecting data for a period of approximately six months, then compare the progress of distinct groups to see which infants started walking first and draw a conclusion accordingly to see whether the new formula influenced how quickly infants started walking.
