Question

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

Answer 1

Answer.

Independent measures design involves use of a different group of participants for each treatment condition and it therefore increase the chance of error that the results would be caused by factors other than the independent variable. Hence, it yields lower internal validity. On the other hand, repeated measures design involves the use of the same group of participants for the different treatment conditions and hence it results in greater internal validity as one can ascertain that the difference between the different treatment groups is by the independent variable alone rather than chance.