Volume 91, Issue 5, May (2004), pp. 765-771 © The Author 2004
doi:10.1079/BJN20041095

Standardised coding of diet records: experiences from INTERMAP UK†

Rana Conway¹, Claire Robertson², Barbara Dennis³, Jeremiah Stamler⁴ and Paul Elliott² for the INTERMAP Research Group
¹Department of Nutrition and Dietetics, Kings College London, 150 Stamford Street, London, SE1 8WA, UK
²Department of Epidemiology and Public Health, Imperial College London, St Mary's Campus, Norfolk Place, London, W2 1PG, UK
³Department of Biostatistics, Collaborative Studies Coordinating Center, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
⁴Department of Preventive Medicine, The Feinberg School of Medicine, Northwestern University, Chicago, IL, USA

 (Received 16 May 2003–Revised 18 December 2003–Accepted 7 January 2004)

Coding diet records is a basic element of most dietary surveys, yet it often receives little attention even though errors in coding can lead to flawed study results. In the INTERnational study of MAcro- and micronutrients and blood Pressure (INTERMAP study), efforts were made to minimise errors in coding the 18720 diet records. Staff were centrally trained and certified before being able to process study data and ongoing quality control checks were performed. This involved the senior (site) nutritionist re-coding randomly selected diet records. To facilitate standardisation of coding in the UK, a code book was designed; it included information about coding brand items, density and portion size information, and default codes to be assigned when limited information was available for food items. It was found that trainees, despite previous experience in coding elsewhere, made coding errors that resulted in errors in estimates of daily energy and nutrient intakes. As training proceeded, the number of errors decreased. Compilation of the code book was labour-intensive, as information from food manufacturers and retailers had to be collected. Strategies are required to avoid repetition of this effort by other research groups. While the methods used in INTERMAP to reduce coding errors were time consuming, the experiences suggest that such errors are important and that they can be reduced.

Keywords:
Nutrient coding, 24h Recall, Standardisation, INTERMAP

Abbreviations:
INTERMAP, INTERnational study of MAcro- and micronutrients and blood Pressure, LSNFR, local site new food request, QC, quality control