The intent of this chapter is to enhance understanding of various dietary assessment methods so that the most appropriate method for a particular need is chosen. This review focuses only on individual level food intake assessment. It is intended to serve as a resource for those who wish to assess diet in a research study using individual measurements for group level analysis. The chapter reviews major dietary assessment methods, their advantages and disadvantages, and validity; describes which dietary assessment methods are appropriate for different types of studies and populations; and discusses specific issues that relate to all methods.

Dietary Assessment Methodology

OBJECTIVES: This study estimated the amount of weight change in a biracial cohort of young adults and the separate components attributable to time-related and aging-related changes, as well as identified possible determinants of weight change. METHODS: In this population-based prospective study of 18- to 30-year-old African-American and White men and women, body weight and prevalence of overweight were measured from 1985/86 to 1992/93. RESULTS: Average weight increased over the 7 years, increases ranging from 5.2 kg (SE = 0.2, n = 811) in White women to 8.5 kg (SE = 0.3, n = 882) in African-American women. Significant time-related increases in weight, ranging from 2.0 kg (SE = 1.0) in White women to 4.8 kg (SE = 1.0, n = 711) in African-American men, accounted for 40% to 60% of the average total weight gain. Aging-related increases were also significant, ranging from 2.6 kg (SE = 0.8, n = 944) in White men to 5.0 kg (SE = 1.1) in African-American women. The prevalence of overweight increased progressively...

Seven-year trends in body weight and associations with lifestyle and behavioral characteristics in black and white young adults: the CARDIA study.

The aim of this report is to describe INTERMAP standardized procedures for assessing dietary intake of 4680 individuals from 17 population samples in China, Japan, UK and USA: Based on a common Protocol and Manuals of Operations, standardized collection by centrally trained certified staff of four 24 h dietary recalls, two timed 24-h urines, two 7-day histories of daily alcohol intake per participant; tape recording of all dietary interviews, and use of multiple methods for ongoing quality control of dietary data collection and processing (local, national, and international); one central laboratory for urine analyses; review, update, expansion of available databases for four countries to produce comparable data on 76 nutrients for all reported foods; use of these databases at international coordinating centres to compute nutrient composition. Chinese participants reported 2257 foods; Japanese, 2931; and UK, 3963. In US, use was made of 17,000 food items in the online automated Nutrition Data System. Average time/recall ranged from 22 min for China to 31 min for UK. Among indicators of dietary data quality, coding error rates (from recoding 10% random samples of recalls) were 2.3% for China, 1.4% for Japan, and UK; an analogous US procedure (re-entry of recalls into computer from tape recordings) also yielded low discrepancy rates. Average scores on assessment of taped dietary interviews were high, 40.4 (Japan) to 45.3 (China) (highest possible score: 48); correlations between urinary and dietary nutrient values--similar for men and women--were, for all 4680 participants, 0.51 for total protein, range across countries 0.40-0.52; 0.55 for potassium, range 0.30-0.58; 0.42 for sodium, range 0.33-0.46. The updated dietary databases are valuable international resources. Dietary quality control procedures yielded data generally indicative of high quality performance in the four countries. These procedures were time consuming. Ongoing recoding of random samples of recalls is deemed essential. Use of tape recorded dietary interviews contributed to quality control, despite feasibility problems, deemed remediable by protocol modification. For quality assessment, use of correlation data on dietary and urinary nutrient values yielded meaningful findings, including evidence of special difficulties in assessing sodium intake by dietary methods.

INTERMAP: the dietary data--process and quality control.

Multiple Risk Factor Intervention Trial

As we have presented, it is evident that cohort studies are confronted with their own special, non-trivial issues of quality assurance and quality control. Such studies are typically large-scale designs and involve an extensive amount of data to be collected and processed, the quality of which depends on a variety of factors related to study personnel and equipment. The fact that data are collected over an extended period of time and at several centers greatly increases the magnitude of the data processing task, significantly increasing the likelihood of discrepancies and measurement error in the data. As presented in tables 1 and 2, the quality assurance and quality control procedures span the entire course of the study and include a multitude of tasks. Such tasks are delegated to various committees and/or are undertaken by participating centers, all of which must take responsibility for understanding, implementing, and following through on all procedures that maximize data quality. The quality of the quality assurance/quality control process is highly correlated with the quality of the communication within and between centers and all researchers. Maintaining standardization of procedures across centers and long-term stability of equipment and analytic procedures are integral components of quality control. In conclusion, the magnitude of the quality control process in a multicenter longitudinal study should not be underestimated, requiring a significant commitment of study resources. The quality control process is key to the integrity of the study, and an integral part of the design of the study. In a well-designed study, with a good quality control process and dedication to the process by the research team, the validity of the conclusions of the cohort study can be established.

P.Victor Grambsch

Papers

Forms control and error detection procedures used at the Coordinating Center of the Multiple Risk Factor Intervention Trial (MRFIT).

Quality control in the Multiple Risk Factor Intervention Trial Nutrition Modality.