TY - JOUR

T1 - Back-transformation of treatment differences - an approximate method

AU - Laursen, Rikke Pilmann

AU - Dalskov, Stine-Mathilde

AU - Damsgaard, Camilla Trab

AU - Ritz, Christian

N1 - CURIS 2014 NEXS 029

PY - 2014

Y1 - 2014

N2 - Background/Objectives:Transformation of outcomes is frequently used in the analysis of studies in clinical nutrition. However, back-transformation of estimated treatment means and differences is complicated by the nonlinear nature of the transformations. It is not straightforward to obtain an estimated treatment difference that can be interpreted without any reference to the additional predictors included in the statistical model; and moreover, standard errors are not easily available. The aim of this work was to provide a generally applicable, yet operational procedure for obtaining back-transformed estimated differences, and corresponding standard errors and 95% confidence intervals.Subjects/Methods:Based on data from two randomized controlled studies and an exemplary data set that had all previously been published, we evaluated our approximate procedure by comparing results for different approaches for showing back-transformed estimated treatment differences.Results:Estimated differences obtained on logarithm, square root and reciprocal square root-transformed scales were back-transformed into estimated differences on the original scales, and these estimates were in good agreement with the results reported by the original studies.Conclusions:The proposed approximate procedure provides a flexible approach for obtaining quite accurate back-transformed estimated differences in terms of medians and for deriving the corresponding standard errors.European Journal of Clinical Nutrition advance online publication, 11 December 2013; doi:10.1038/ejcn.2013.259.

AB - Background/Objectives:Transformation of outcomes is frequently used in the analysis of studies in clinical nutrition. However, back-transformation of estimated treatment means and differences is complicated by the nonlinear nature of the transformations. It is not straightforward to obtain an estimated treatment difference that can be interpreted without any reference to the additional predictors included in the statistical model; and moreover, standard errors are not easily available. The aim of this work was to provide a generally applicable, yet operational procedure for obtaining back-transformed estimated differences, and corresponding standard errors and 95% confidence intervals.Subjects/Methods:Based on data from two randomized controlled studies and an exemplary data set that had all previously been published, we evaluated our approximate procedure by comparing results for different approaches for showing back-transformed estimated treatment differences.Results:Estimated differences obtained on logarithm, square root and reciprocal square root-transformed scales were back-transformed into estimated differences on the original scales, and these estimates were in good agreement with the results reported by the original studies.Conclusions:The proposed approximate procedure provides a flexible approach for obtaining quite accurate back-transformed estimated differences in terms of medians and for deriving the corresponding standard errors.European Journal of Clinical Nutrition advance online publication, 11 December 2013; doi:10.1038/ejcn.2013.259.

U2 - 10.1038/ejcn.2013.259

DO - 10.1038/ejcn.2013.259

M3 - Journal article

C2 - 24327119

VL - 68

SP - 277

EP - 280

JO - European Journal of Clinical Nutrition

JF - European Journal of Clinical Nutrition

SN - 0954-3007

IS - 2

ER -