study designs

A factorial study design (or fully crossed design) is a type of experimental study design that utilizes >2 interventions and all combinations of these interventions. In this study, there were 2 main interventions (antioxidant or glutamine supplementation) resulting in 4 possible study arms: glutamine supplementation, antioxidant supplementation, both, and neither (ie, placebo).

Although the authors randomized patients to these 4 arms, the results in the table provided are based on exposure or lack thereof to glutamine/antioxidant.

(Choice D) A nested study (or nested case-control study) is a form of retrospective observational study in which subsets of controls are matched to cases and analyzed for the variables of interest.