Analyze each of the following arguments in terms of the variation of the “phenomena” to show how they follow the pattern of the method of concomitant variation:

Prof. Kathleen Vohs reports that two groups of college students were asked to read out loud from “a boring book on the biographies of scientists.” One of the groups was obliged to wear fake expressions of delight and interest, while the other group was allowed to read the same texts naturally. Each group was afterward given a sum of money to spend on an assortment of goods, or to save. Those who had been faking delight spent 62 percent more than those who had not. Similarly, a group of students writing down their thoughts without restraint spent very much less than a similar group obliged while writing to avoid all thoughts about white bears. The more self-restraint that a person expends to control one impulse, it appears, the less self-restraint is available to control others.
—Reported in Journal of Consumer Research, March 2007