consider a single study that seeks to compare four diets (low-fat, low-carb, zone, and dash), plus a control condition. two hundred participants are randomly assigned and trained to follow one of the four diets or are assigned to the control condition in which they receive training on general healthy eating. approximately 40 participants are assigned to each of the five groups. each participant's weight is recorded before and after the study period. why can't you test whether there are differences in the mean weight loss for each condition using a single two-sample t test?