Dr. Yi Guo’s tutorial “Selecting a sample size for studies with repeated measures” has been labeled “Highly Accessed” and listed under “Most Viewed” on the BMC Medical Research Methodology website. In this tutorial, Dr. Guo describes methods for gathering the information required for selecting a sample size for studies with repeated measurements of normally distributed continuous responses. Dr. Guo also illustrates the process of selecting a sample size to power a treatment by time interaction by working through an example with repeated measurements of pain memory using GLIMMPSE. The tutorial was published on July 31, 2013 and has already been accessed 833 times. Congratulations to Dr. Guo and to co-authors Dr. Keith Muller, Dr. Deb Glueck, and Dr. Henrietta Logan!