Improved interpretation of studies comparing methods of dietary assessment: combining equivalence testing with the limits of agreement

Abstract

The aim of this study was to demonstrate the use of testing for equivalence in combination with the Bland and Altman method when assessing agreement between two dietary methods. A sample data set, with eighty subjects simulated from previously published studies, was used to compare a FFQ with three 24 h recalls (24HR) for assessing dietary I intake. The mean I intake using the FFQ was 126·51 (SD 54·06) µg and using the three 24HR was 124·23 (SD 48·62) µg. The bias was −2·28 (SD 43·93) µg with a 90 % CI 10·46, 5·89 µg. The limits of agreement (LOA) were −88·38, 83·82 µg. Four equivalence regions were compared. Using the conventional 10 % equivalence range, the methods are shown to be equivalent both by using the CI (−12·4, 12·4 µg) and the two one-sided tests approach (lower t = −2·99 (79 df), P = 0·002; upper t = 2·06 (79 df), P = 0·021). However, we make a case that clinical decision making should be used to set the equivalence limits, and for nutrients where there are potential issues with deficiency or toxicity stricter criteria may be needed. If the equivalence region is lowered to ±5 µg, or ±10 µg, these methods are no longer equivalent, and if a wider limit of ±15 µg is accepted they are again equivalent. Using equivalence testing, acceptable agreement must be assessed a priori and justified; this makes the process of defining agreement more transparent and results easier to interpret than relying on the LOA alone.

Prediction of 24-hour sodium excretion from spot urine samples in South African adults: a comparison of four equations

“…The Mage equation performed the worst, with a mean overestimation of 55% but unacceptably wide limits of agreement (LOA: 57% underestimation to 1321% overestimation). Clearly, this level of bias is outside the scope of an acceptable range [47].…”

Iodine Status Assessment in South African Adults According to Spot Urinary Iodine Concentrations, Prediction Equations, and Measured 24-h Iodine Excretion

“…For predicted 24 h UIE, based on spot UIC concentrations, all three prediction equations resulted in average under-estimations, ranging from 17% to 32 % for the different equations, with accompanying unacceptably wide limits of agreement. The difficulty of deciding on clinically relevant acceptable limits of agreement has previously been discussed by various authors [ 37 , 38 ]. In the case of iodine, for populations where intakes may be inadequate and where the consequences of inadequacy have serious impacts on health outcomes, such as in the case of pregnant women, more stringent cut-offs for determining acceptable limits of agreement may be warranted.…”

Development, validation and reproducibility of a food frequency questionnaire to measure flavonoid intake in older Australian adults

“…This clearly indicates a lack of equivalence between the two methods. Formal equivalence testing was not conducted in the present study, although this has recently been recommended by Batterham et al . and may be a consideration in future studies.…”