Validation of clinic weights from electronic health records against standardized weight measurements in weight loss trials

Abstract

Objective: To validate clinic weights in electronic health records against researcher-measured weights for outcome assessment in weight loss trials.

Methods: Clinic and researcher-measured weights from a published trial (BE WELL) were compared using Lin's concordance correlation coefficient, Bland and Altman's limits of agreement, and polynomial regression model. Changes in clinic and researcher-measured weights in BE WELL and another trial, E-LITE, were analyzed using growth curve modeling.

Results: Among BE WELL (n = 330) and E-LITE (n = 241) participants, 96% and 90% had clinic weights (mean [SD] of 5.8 [6.1] and 3.7 [3.9] records) over 12 and 15 months of follow-up, respectively. The concordance correlation coefficient was 0.99, and limits of agreement plots showed no pattern between or within treatment groups, suggesting overall good agreement between researcher-measured and nearest-in-time clinic weights up to 3 months. The 95% confidence intervals for predicted percent differences fell within ±3% for clinic weights within 3 months of the researcher-measured weights. Furthermore, the growth curve slopes for clinic and researcher-measured weights by treatment group did not differ significantly, suggesting similar inferences about treatment effects over time, in both trials.

Conclusions: Compared with researcher-measured weights, close-in-time clinic weights showed high agreement and inference validity. Clinic weights could be a valid pragmatic outcome measure in weight loss studies.

Trial registration: ClinicalTrials.gov NCT00842426 NCT00901095.

Conflict of interest statement

The authors declare no conflict of interest.

© 2017 The Obesity Society.

Figures

Figure 1

Bland and Altman’s limits of agreement plots. The plots illustrate the differences between clinic and research weights (y-axis, in kg) and the lower and upper bounds for the 95% limits of agreement (horizontal dashed lines, mean of differences ± 1.96 standard deviation) against the means of these measurements (x-axis, in kg) in the BE WELL trial. Two index windows, 1 and 3 months, were applied to capture the closest clinic weight in time in comparison to research weights measured at baseline, 6 and 12 months.

Figure 2

Polynomial regression model results. The graphs show the predicted percentage weight differences, (clinic weight-research weight)/research weight, in kg, and the 95% CIs (left) or the numbers of participants with available clinic and research weight (right) versus days between clinic and research weight measurements by study time point. The coefficients for the treatment group-by-days interaction term were not statistically significant at baseline and 12 months. Thus, separate regression lines by treatment group are shown at 6 months only.