The Impact of Dietary Measurement Error on Planning Sample Size Required in a Cohort Study

Abstract

Dietary measurement error has two consequences relevant to epidemiologic studies: first, a proportion of subjects are misclassified into the wrong groups, and second, the distribution of reported intakes is wider than the distribution of true intakes. While the first effect has been dealt with by several other authors, the second effect has not received as much attention. Using a simple errors-in-measurement model, the authors investigate the implications of measurement error for the distribution of fat intake. They then show how the inference of a more narrow distribution of true intakes affects the calculation of sample size for a cohort study. The authors give an example of the calculation for a cohort study investigating dietary fat and colorectal cancer. This shows that measurement error has a profound effect on sample size, requiring a six- to eightfold increase over the number required in the absence of error, if the correlation coefficient between reported and true intakes is 0.65. Reliable detection of a relative risk of 1.36 between a true intake of greater than 47.5% calories from fat and less than 25% calories from fat would require approximately one million subjects.

Validation of the Food Frequency Questionnaire Used to Assess the Association between Dietary Habits and Cardiovascular Risk Factors in the NESCAV Study

“…However, in the NESCAV study, our main concern was to classify individuals into different groups according to exposure levels rather than to assess their absolute nutrients intake. Indeed, for estimating relative risks between nutritional exposure and cardiovascular risk factor, the degree of misclassification of subjects is more important than the quantitative scale on which the ranking is made [28]. Therefore, correlations and weighted kappa were also computed.…”

Exposure Measurement Error: Influence on Exposure-Disease Relationships and Methods of Correction

“…Freedman et al (15) have discussed the impact of measurement error on sample size needs for cohort studies. For example, if the correlation between x and z is 0.…”

A bivariate measurement error model for nitrogen and potassium intakes to evaluate the performance of regression calibration in the European Prospective Investigation into Cancer and Nutrition study

“…The accuracy of dietary assessment instruments used in nutritional epidemiology studies, that is, questionnaires such as food frequency questionnaires or dietary histories, has been repeatedly questioned (Freedman et al, 1990;Schatzkin et al, 2003;Kristal et al, 2005), as it is recognized that they are subject to random and systematic measurement errors . In the past decade, epidemiological investigations aimed at quantifying the association between diet and risk of chronic disease(s) have often integrated data from dietary questionnaires, completed by all study subjects, with reference instruments, usually 24-h dietary recalls (24-HDRs), administered to a subsample of the study (Thompson et al, 1997;Riboli and Kaaks, 2000;Stram et al, 2000).…”