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Sources of Error in Dietary Surveys.

1945; Springer Science+Business Media; Volume: 36; Issue: 9 Linguagem: Inglês

1920-7476

E.W. McHenry, Helen P. Ferguson, John Gurland,

Metabolism and Genetic Disorders

TOURING the past ten years dietary surveys have become more common. The ^ general procedure has consisted of securing records of food purchases or of food intakes, the subsequent calculation of the amounts of various nutrients, and the assessment of these amounts in terms of a set of standards. From these surveys conclusions have been drawn regarding the occurrence of nutritional deficiencies and, in some cases, the conclusions have been sweeping in nature. While evidence of frank deficiency states is on firm ground, the bulk of the data regarding the occurrence of so-called subclinical deficiency rests upon the results of dietary surveys. Comparatively little attention has been given to errors which may be common to all dietary surveys and which may vitiate the validity of the results. Several groups of investigators (1, 2) have pointed out that customary interpretations of dietary surveys do not correlate with clinical findings. This lack of agreement may be due to faults in either or both approaches to the determination of nutritional conditions. In considering the validity of results of dietary surveys several types of error should be listed : 1 . If inferences regarding dietary conditions in a population are to be drawn from a survey of a sample of the population, it is essential that the sample be representative. While specifications may be constructed by statisticians regarding the procedure to be followed in securing a representative sample, the actual sample obtained may be quite different from that specified. It is necessary to secure voluntary co-operation of individuals or families and this is not always possible. If the sample is not representative, it would seem advisable to limit the inferences to the particular group studied. 2. There may be considerable difference between food consumption for a short period and sustained food habits. It may be that food consumption for the period studied was exceptional because the subjects were under observation and were influenced in the choice of food by the scrutiny. Even if that factor is not operating, the constancy of intake of various nutrients is open to question. Because a person has a low intake of thiamin on one day or during one week, there is no assurance that he has had such a supply for some time or is so accustomed. It is common practice to conclude from a survey of perhaps one week that the results represent the nutritional conditions in the sample of the population ; this ignores variability in food intake. It is unlikely that the nutritional status of an individual will be influenced by a low intake for a single day or for a short period. 3. Aside from variability, the record of food intake may not have been accurately made. In the type of survey in which food purchases, or indeed food consumption, are recorded by trained observers, one may conclude that reasonably accurate records are obtained. In cases in which the recording is done by the subjects, the data are frequently open to question. In many surveys estimates