@ChrisHemedinger Thank you for your advice. I have SAS studio. I had a look to the tutorial but what I do not know is whether I need to merge the all NHANES data sets (diet interviews, demographics, past medical history/risk factors, cognitive functions tests etc...) prior to do my analyses, which seems for me more logical if I want to assess the impact of diet on cognitive functions and take into account confounders. if I need to merge them, it should be one after one or can I merge all simultaneously? thanks for any advice.
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