Question

Q. What is the major difference between independent groups and repeated measures designs in terms of addressing internal validity?

Answer 1

an experiment involves two main ways of allocating participants to the different conditions. The most widely used designs are a repeated measures design or an independent measures design. An independent measures design assigns participants to separate groups and Each of the groups is then designated to a single research condition. because different participants are used in every condition the effect of individual differences on the scores for each condition is much greater. Therefore, independent design can lead to low internal validity.

On the other hand,  repeated measures design has only one group of participants who complete every research condition and fewer participants are needed to run an experiment. This yields greater internal validity and reliability as individuals in each condition are the same.