The effect of missing data in the supplements to McCance and Widdowson's food tables on calculated nutrient intakes

Objective: To assess the degree of underestimation of nutrient intakes caus ed by missing data in McCance and Widdowson's food tables and supplements, the standard food tables used in the UK. Subjects: 1026 children aged 18 months. Setting: A research clinic in Bristol. Interventions: A 3-day dietary diary was completed for each child. These we re coded and analysed using a database consisting of the unedited informati on in the food tables, to produce a set of 'uncorrected' nutrient intakes. 'Guesstimated' values for nutrient content were then added to our nutrient database in place of the missing values in the food tables, and the daily n utrient intakes were recalculated. Main outcome measures: Calculated daily nutrient intakes before and after s ubstituting missing data in the food tables for guesstimated values. Results: Of the 1027 foods used in the analysis, 540 had missing data for o ne or more nutrient content. For several of the nutrients examined adding g uesstimated values altered the calculated nutrient intake of more than 90% of the subjects. However, for nutrients such as the B vitamins and the majo r minerals the mean percentage underestimate was very small. We calculated the underestimation of nutrient intake to be largest for vitamins E and D ( 13.8% and 14.7%, respectively). The effect of missing data on calculated nu trient intakes was proportionately greater at the bottom end of the nutrien t intake distribution. Conclusion: Missing data has a fairly small effect on calculated mean daily intakes. However, it can result in some individuals being misranked within a nutrient intake distribution. The availability of a standard set of 'gue sstimates' to use in place of missing data would reduce this problem, and w ould improve comparability between dietary surveys. Sponsor: University of Bristol. Descriptors: food tables; missing nutrient data.