Villegas et al (2007) Validity and reproducibility of the Food Frequency Questionnaire used in the Shanghai men’s health study. British Journal Nutrition, 97, 993-1000
The accurate estimates of food intake over long periods is a real necessity and poses a methodology problem for diet-disease research. .One method is the Food Frequency Questionnaire. Short-term recalls and diet records are expensive and not very accurate. Especially in taking diet histories from the past. Food Frequency Questionnaires have been the primary method of dietary assessment for most epidemiological studies. Food Frequency Questionnaire are easy and cheap to use They are however very sensitive to the cultural and dietary practices of populations. .The food list which the questionnaire is based is very important. The list shown to the population being studied must contain the foods eaten by that population,
The validity and reliability of an FFQ needs to be evaluated for the specific population being studied. of concern. In many epidemiological studies, however, the main concern is to classify individuals into different groups according to exposure levels rather than to assess their absolute intake. Thus, comparisons of percentage agreement in quartile distributions are also often used in the evaluation of the validity and reliability of a Food Frequency Questionnaire.
The validity and reproducibility of Food Frequency Questionnaires in multiethnic populations has been investigated before. For absolute nutrient intakes, the correlations were greatest for whites, somewhat lower for Japanese-Americans and Latinos, and lowest for African-Americans . A complication is food choice. In Shanghai, women are mainly responsible for purchasing and preparing foods for the family and. thus, are more likely to estimate their dietary intake accurately than men.
Villegas and his colleagues believe that the dietary recall information obtained from this study is a fairly accurate measurement of the true usual intake for this study population over a 1-year period. Multiple dietary recalls may sensitise study participants regarding their dietary intake, and thus participants may answer the Food Frequency Questionnaire more accurately, resulting in an overestimation of intake. On the other hand, changes in dietary intake during the year must also be identified.
Food Frequency Questionnaires overestimate soy. fruit and vegetable intake, and slightly underestimated poultry, red meat, fish and egg intake. Some of the measurement error may reflect a bias of study participants seeking social approval.
Villegas and colleagues concluded that Food Frequency Questionnaires appropriate for the population under study can reasonably categorise usual intake of major nutrients and food groups. Food Frequency Questionnaires. may under- or overestimate the absolute amount of intake of some nutrients or foods.
- Martin Eastwood