title: Missing data in FFQs: making assumptions about item non-response.
abstract: OBJECTIVE
  FFQs are a popular method of capturing dietary information in epidemiological studies and may be used to derive dietary exposures such as nutrient intake or overall dietary patterns and diet quality. As FFQs can involve large numbers of questions, participants may fail to respond to all questions, leaving researchers to decide how to deal with missing data when deriving intake measures. The aim of the present commentary is to discuss the current practice for dealing with item non-response in FFQs and to propose a research agenda for reporting and handling missing data in FFQs.
  
  
  RESULTS
  Single imputation techniques, such as zero imputation (assuming no consumption of the item) or mean imputation, are commonly used to deal with item non-response in FFQs. However, single imputation methods make strong assumptions about the missing data mechanism and do not reflect the uncertainty created by the missing data. This can lead to incorrect inference about associations between diet and health outcomes. Although the use of multiple imputation methods in epidemiology has increased, these have seldom been used in the field of nutritional epidemiology to address missing data in FFQs. We discuss methods for dealing with item non-response in FFQs, highlighting the assumptions made under each approach.
  
  
  CONCLUSIONS
  Researchers analysing FFQs should ensure that missing data are handled appropriately and clearly report how missing data were treated in analyses. Simulation studies are required to enable systematic evaluation of the utility of various methods for handling item non-response in FFQs under different assumptions about the missing data mechanism.
authors.affiliation: 1Institute for Physical Activity and Nutrition,School of Exercise and Nutrition Sciences,Deakin University,221 Burwood Highway,Burwood,VIC 3125,Australia.
authors.forename: Karen E
authors.initials: KE
authors.lastname: Lamb
authors.affiliation: 1Institute for Physical Activity and Nutrition,School of Exercise and Nutrition Sciences,Deakin University,221 Burwood Highway,Burwood,VIC 3125,Australia.
authors.forename: Dana Lee
authors.initials: DL
authors.lastname: Olstad
authors.affiliation: 2Department of Paediatrics,University of Melbourne,Parkville,VIC,Australia.
authors.forename: Cattram
authors.initials: C
authors.lastname: Nguyen
authors.affiliation: 1Institute for Physical Activity and Nutrition,School of Exercise and Nutrition Sciences,Deakin University,221 Burwood Highway,Burwood,VIC 3125,Australia.
authors.forename: Catherine
authors.initials: C
authors.lastname: Milte
authors.affiliation: 1Institute for Physical Activity and Nutrition,School of Exercise and Nutrition Sciences,Deakin University,221 Burwood Highway,Burwood,VIC 3125,Australia.
authors.forename: Sarah A
authors.initials: SA
authors.lastname: McNaughton
mesh_terms: D003625:Data Collection; D003627:Data Interpretation, Statistical; D004032:Diet; D004034:Diet Surveys / Q000592:standards*; D063427:Food Quality; D006801:Humans; D015233:Models, Statistical; D015596:Nutrition Assessment
keywords: Dietary assessment; FFQ; Imputation; Item non-response; Missing data