Hunter D J, Sampson L, Stampfer M J, Colditz G A, Rosner B, Willett W C
Department of Medicine, Harvard Medical School, Boston, MA.
Am J Epidemiol. 1988 Jun;127(6):1240-9. doi: 10.1093/oxfordjournals.aje.a114916.
The use of food frequency questionnaires for measuring dietary intake has become widespread in epidemiologic studies. It has been suggested that inquiring about a person's usual serving size of each food, in addition to the frequency of consumption, will improve the accuracy of this method. This approach implies that individuals characteristically eat a specific amount of any particular food, and that this amount can be reported with reasonable accuracy. To investigate the variability of portion sizes, the authors analyzed data for 68 commonly consumed foods, based on four one-week weighed diet histories recorded by 194 Boston-area women aged 34-59 years during 1980 and 1981. For each food, total population variance in portion size was partitioned into within-person (intraindividual) and between-person (interindividual) components. For all but seven food items (yogurt, liver, mixed vegetables, watermelon, pancakes/waffles, cold cereal, and cooked cereal) the within-person variance in portion size exceeded the between-person variance. The mean of the within-person to between-person variance ratios, after exclusion of two outlying foods, was 3.4 for untransformed portion sizes, and 3.2 after portion sizes were loge-transformed. Foods with a high within-person variance also tended to have a high between-person variance. The dominance of within-person variance in portion sizes suggests that the concept of usual portion size is complex, and that subjects may experience substantial difficulty in specifying their "usual" portion size. The smaller contribution of between-person variance to the total variance in portion size suggests that specification of a standard portion size by the investigator may not introduce a large error in the estimation of food and nutrient intake.
在流行病学研究中，使用食物频率问卷来测量饮食摄入量已变得十分普遍。有人提出，除了询问食物的食用频率外，询问一个人每种食物的通常食用量，将提高这种方法的准确性。这种方法意味着个体通常会食用特定数量的任何一种特定食物，并且这个数量可以较为准确地报告出来。为了研究食用量的变异性，作者分析了68种常见食物的数据，这些数据基于194名年龄在34 - 59岁的波士顿地区女性在1980年和1981年记录的四份为期一周的称重饮食记录。对于每种食物，食用量的总体方差被分为个体内（个体内部）和个体间（个体之间）两个部分。除了七种食物（酸奶、肝脏、混合蔬菜、西瓜、煎饼/华夫饼、冷谷物和熟谷物）外，其他所有食物的个体内食用量方差都超过了个体间方差。在排除两种极端食物后，未转换食用量时个体内与个体间方差比的平均值为3.4，对食用量进行自然对数转换后为3.2。个体内方差高的食物往往个体间方差也高。食用量中个体内方差占主导地位表明，通常食用量的概念很复杂，而且受试者在确定自己的“通常”食用量时可能会遇到很大困难。个体间方差对食用量总方差的贡献较小，这表明研究者指定标准食用量可能不会在食物和营养摄入量的估计中引入很大误差。
