A recent study claims that a particular herbal supplement has remarkable health benefits, including reducing the risk of heart disease and improving cognitive function. Proponents argue that this study is groundbreaking and should lead to widespread use of the supplement for its potential health benefits. Critics, however, argue that the study's methodology and sample size are questionable, and more rigorous investigation is needed before drawing such conclusions. Which of the following would it be most useful to determine in order to evaluate the argument?