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:

The notion that poverty and mental illness are intertwined is not new—but finding evidence that one begets the other has often proved difficult. New research, which coincided with the opening of a new gambling casino on an Indian reservation, appears to strengthen that link, strongly suggesting that lifting children out of poverty (as casino income did in many cases) tends to diminish some (but not all) psychiatric symptoms.

A study published in the Journal of the American Medical Association in October 2003 tracked 1,420 children, ages 9 to 13, in rural North Carolina, very many of whom lived on a Cherokee Indian reservation. During the study a casino that had been opened on the reservation began distributing some of its profi ts to tribal families, the payments reaching about $6,000 per year by 2001. The researchers found that the rate of psychiatric symptoms among the children who had risen from poverty dropped steadily; those children were less inclined to temper tantrums, stealing, bullying, and vandalism—common symptoms of oppositional defiant disorders. Children whose families rose above the poverty threshold showed a 40 percent decrease in behavioral symptoms. The rate of such behaviors, after four years, dropped to the same levels found among children whose families had never been poor. But the casino payments had no effect on children whose families were nevertheless unable to rise from poverty, or on those children whose families had not been poor to begin with.

The economic change had a significant effect on only a fraction of the children followed. This, it was hypothesized, was a consequence of the fact that, although all the families that received the payment received the same amount of money, the payments resulted in lifting only 14 percent of those families above the poverty line which, in 2002, was $14,348 for a family of three. The study suggests, said Dr. Arline Geronimus, of the University of Michigan, that poverty puts stress on families, which can increase the likelihood that children will develop behavioral problems.