"It might seem an extremely easy matter to obtain accurate records of food consumed. Experience shows that it is not so. At the foot of the social scale there is a residue of housewives who are incapable of keeping accurate records, even with help and supervision. The work of Dr A. M. Thomson (unpublished) on shows that those unable to keep records are, almost certainly, worse fed than the more intelligent. In most surveys they swell the proportion of non-cooperators. But in all social and intellectual grades, vigilance is needed. Even highly intelligent scientists have been found grossly inaccurate in attempts to record what they ate the day before (Morrison, Russell & Stevenson, 1949)."