Table 5.
– FM by DXA and BIS for the Roux-en-Y Gastric Bypass Longitudinal Data Set.
| Timepoint | n | Mean difference, kg | r | RMSE, kg | CCC | r2 | B-A Limits of agreement | FMChamney, kg | DXAFM, kg | B-A PE | r2 for the regression line through the B-A plot (P-value) |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Pre-RYGB | 25 | −7.6 ± 6.7* | 0.93* | 6.47 | 0.81 | 0.86 | −20.8 to 5.5 | 71.8 ± 17.2 | 64.1 ± 13.8 | 20% | 0.27 (0.008) |
| 6-months post-RYGB | 16 | −6.3 ± 5.9* | 0.94* | 5.80 | 0.85 | 0.88 | −17.8 to 5.2 | 50.6 ± 16.3 | 44.3 ± 13.6 | 26% | 0.22 (0.07) |
| 1-year post-RYGB | 15 | −7.2 ± 4.3* | 0.98* | 3.45 | 0.86 | 0.96 | −15.7 to 1.3 | 40.3 ± 16.4 | 33.2 ± 13.3 | 26% | 0.53 (0.002) |
| Δ Baseline to 6-months | 16 | 1.3 ± 5.3 | 0.68* | 4.26 | 0.64 | 0.46 | −9.1 to 11.8 | −26.5 ± 5.6 | −25.2 ± 7.2 | - | 0.11 (0.22) |
| Δ Baseline to 1-year | 15 | 0.36 ± 5.1 | 0.84* | 4.99 | 0.84 | 0.71 | −9.6 to 10.3 | −35.6 ± 8.9 | −35.2 ± 9.2 | - | 0.002 (0.87) |
| Δ 6-months to 1-year | 14 | −1.3 ± 2.8 | 0.88* | 2.83 | 0.86 | 0.78 | −6.9 to 4.2 | −9.2 ± 5.7 | −10.6 ± 5.9 | - | 0.002 (0.87) |
Abbreviations: FM, fat mass; DXA, dual energy X-ray absorptiometry; BIS, bioimpedance spectroscopy; RYGB, Roux-en-Y gastric bypass; RMSE, root mean square error; CCC, concordance correlation coefficient; B-A, Bland-Altman analysis; FMChamney, FM calculated from the Chamney model using BIS-generated BMI-adjusted ECWMoissl and ICWMoissl; B-A percent error (PE) calculated as limits of agreement for the difference between the two methods (1.96(SD)) divided by the mean for the reference DXA method × 100%. PE not calculated for FM change intervals because the magnitude of error in all cases was greater than the mean difference between methods. Values are reported as mean ± SD unless otherwise noted.
indicates significantly different, P-value <0.001