The National Health and Nutrition Examination Survey the National (NHANES) is a population-based health survey of non-institutionalized U. S. residents. NAHNES participants complete extensive health and nutrition surveys, undergo a series of physical exams and health screenings, and give biological samples for a predetermined battery of tests. Public use data sets are available for researchers. Among participants enrolled in 2001, researchers explored the association between levels of 12 pesticides (measured in blood that was collected at enrollment) and cognitive function (which was assessed by the Digit-Symbol Coding test taken by each study participate at the same study visit). The researchers adjusted the analyses for age, education, race/ethnicity, and income. (Bouchard et. al. 2013) 1a. What is the study design? (1 points) 1.b. Briefly explain why (1.5 Points)