Analyze each of the following investigations, or arguments, and indicate which of the methods of causal reasoning—Mill’s methods—are being used in each of them:

Strong evidence has been presented that a diet low in folic acid [a trace vitamin in
the B complex] during pregnancy increases the chances of giving birth to a premature baby of lower than normal birth weight. Dr. Theresa Scholl [of the University of Medicine and Dentistry of New Jersey] studied the outcomes of pregnancy for 832 women from the inner city of Camden, N.J., to determine the influence of dietary and supplementary consumption of folic acid. “We found that the women who consumed less than 240 micrograms per day of folic acid had about a two- to threefold greater risk of preterm delivery and low birth weight,” she said. She reported that even small increases in the women’s serum folic acid concentrations by the 28th week decreased the odds of preterm delivery as well as the chance of having a baby of low birth weight. Of the 219 women in the low-folic-acid category (receiving less than 240 micrograms a day), 44 had preterm, low-birth-weight infants. “The risks declined in direct relationship to increased serum levels of folic acid, showing that low intake is a risk factor throughout pregnancy,” Dr. Scholl concluded.
—T. O. Scholl, et al., “Dietary and Serum Folate: Their
Influence on the Outcome of Pregnancy,” American
Journal of Clinical Nutrition, April 1996