Final answer:
The main advantage of repeated measures designs over randomized group designs is that fewer participants are needed, due to all subjects receiving both treatments. Repeated measures also reduce variability from individual differences, providing clearer condition comparisons.
Step-by-step explanation:
The advantage of repeated measures over randomized groups designs is that fewer participants are needed. This is because all subjects experience both treatments, which enhances efficiency and reduces costs associated with recruiting a large number of participants. Additionally, because each subject acts as their own control, the variability due to individual differences is reduced, allowing for potentially clearer comparisons between conditions.
However, it's important to note that repeated measures designs may introduce order effects, where the sequence in which treatments are administered can impact the results. Consequently, careful consideration and counterbalancing are often employed to mitigate these effects. In contrast, randomized group designs are less susceptible to order effects since different individuals are exposed to different conditions, but they require larger sample sizes to account for individual variability and to achieve comparable statistical power.