[Data File Sheet Name: DOEM 3.4]. A cycling club is trying to determine which tire brands should it use for its next competitive cycling tour. As the tires from a list of manufacturers claim very similar specifications and performances. So, they decided to conduct a study on tires from 20 different manufacturers. To minimize the number of experiments, first they decided to choose three tire brands randomly and collect data on them with respect to the riding speed. They randomly selected 90 riders and installed the three different tire brands, producing 30 replications for each brand. The riders are considered identical, but independent twins (identical and independent experimental units). The diagnostic analysis shows violation for which of the following assumptions?
