Regarding limitations of this study which cannot be avoided as follows: a) Researcher should be careful on
loosing subjects, or missing data during the repeated measured data collection and try to prevent rather than to solve
the problem; b) There should be some other ways to select the appropriate number of classes necessary to employ
LTA-MRA analysis besides program R. Another option is to analyze using different number of classes, and
compare the results in order to seek for the best one; c) The risk occur because of the violation of assumptions of
random sampling should be reconsidered as well