Epidemiological assessment of diet: a comparison of a 7-day diary with a food frequency questionnaire using urinary markers of nitrogen, potassium and sodium.
Day N, McKeown N, Wong M, Welch A, and Bingham S
International Journal of Epidemiology. May 2001
(DOI : 10.1093/ije/30.2.309)
Validation studies in epidemiology: the relative precision of different designs.
Journal of epidemiology and biostatistics. Mar 2001