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Table 5 The method of triads and its extensions in the assessment of ‘relative validity’

From: Systematic review of statistical approaches to quantify, or correct for, measurement error in a continuous exposure in nutritional epidemiology

Reference outlining the method Classical measurement error model assumed Requirements of calibration study Relationship between reference instrument and dietary instrument of interest. Aim of the approach
Method of Triads [105] Yes Three methods of assessment of dietary intake to be available (e.g. FFQ, 24-h dietary recalls and a biomarker) The minimal statistical requirements are that the measurements from the three instruments are linearly related to the true intake levels and their random errors are statistically independent (i.e. uncorrelated). To assess the ‘relative validity’ of dietary intake when the quantitative information was available for three methods (usually FFQ, 24-h dietary recalls and a biomarker).
Method of Triads Extension 1(MOTEX1) [2004] [27] No Superior or gold standard reference instrument available The correlation between errors in the dietary instrument of interest and reference instrument can be non-zero (i.e. the errors are not statistically independent). Aim to estimate the magnitude of correlations between errors in reference and the dietary instrument of interest (e.g. a FFQ).
Method of Triads Extension 2 (MOTEX2) [2005] [36] No Multiple dietary assessment methods required (e.g. self-reported instruments and biomarkers). Three surrogate variables questionnaire (Q); M, and P where M and P are both instrumental (often biological) variables. No conventional reference instrument is required. M and P can be concentration biomarkers rather than recovery biomarkers. To estimate the correlation between a dietary instrument of interest (Q) and true intake (T).
Method of Triads Extension 3 (MOTEX3) [2007] [35] No Multiple dietary assessment methods required (e.g. self-reported instruments and biomarkers). No conventional reference instrument is required. Requires that error correlations between dietary estimates and biomarkers or between biomarkers be close to zero. M, and P are biomarkers with M being a direct measure of dietary intake and M and P are chose so that one has a long half-life and the other a short half-life. Aimed to produce corrected estimates of the effects on an outcome variable of changing the true exposure variables by one standard deviation, a standardized regression calibration.