Reduced dietary questionnaires in case-control studies: some methodological aspects

In epidemiological studies on dietary habits (case-control or cohort studies), usually the goal is not to quantify the absolute nutrients intake for each individual, but to rank the subjects according to the level of consumption of the nutrients. For this reason, dietary questionnaires with a limited number of questions, but neverthless able to reproduce the inter-individual variability of intake for some specific nutrients, should be developed. The goal is to define short questionnaires providing estimates of consumprion highly correlated to the true intake. We present a procedure developted to obtain a reduced dietary questionnaire (RDQ) from a more complex questionnaire already used for investigating the Italian diet.