Measurement of Weight in Clinical Trials: Is One Day Enough?

Table 1

Mean weight change (standard deviation) and weight variability among control participants in weight loss ${\text{maintenance}}^{\text{a}}.$

	All	${\text{Overweight}}^{\text{b}}$	${\text{Obese}}^{\text{c}}$	${\text{Men}}^{\text{d}}$	${\text{Women}}^{\text{d}}$	African	Non-African
						${\text{american}}^{\text{d}}$	american${}^{\text{d}}$
N	316	134	158	113	203	113	203
Baseline characteristics
Mean age (SD), years	55.8 (8.5)	57.3 (8.2)	54.9 (8.4)	56.6 (8.6)	55.4 (8.5)	53.5 (9.0)	57.1 (8.0)
% Female	64.2	61.9	67.1	0	100	71.7	60.1
% African American	35.8	26.9	44.9	28.3	39.9	100	0
% Overweight	42.4	100	0	45.1	40.9	31.9	48.3
% Obese	50	0	100	46	52.2	62.8	42.9
Mean BMI (SD), kg/m^2	30.8 (4.5)	27.7 (1.4)	34.5 (3.2)	30.3 (4.1)	31.2 (4.7)	32.1 (4.9)	30.1 (4.1)
Mean weight, kg	86.9 (15.0)	78.4 (8.8)	96.6 (13.4)	94.7 (15.1)	82.5 (13.1)	89.5 (15.9)	85.4 (14.3)
N for 12-month analysis	309	131	155	109	200	110	199
12-Month weight Δ (SD), kg
Single day	3.9 (5.1)	3.5 (4.3)	4.5 (5.7)	3.9 (5.8)	3.9 (4.6)	3.6 (4.4)	4.0 (5.4)
Two days	3.9 (5.0)	3.5 (4.2)	4.5 (5.7)	3.9 (5.8)	3.9 (4.5)	3.6 (4.4)	4.1 (5.3)
N for 30-month analysis	281	116	141	104	177	101	180
30-Month weight Δ (SD), kg
Single day	6.0 (6.3)	5.7 (5.1)	6.4 (7.4)	6.7 (8.0)	5.5 (5.0)	5.4 (5.0)	6.2 (6.9)
Two days	6.0 (6.3)	5.8 (5.0)	6.4 (7.4)	6.6 (8.1)	5.6 (4.9)	5.4 (5.0)	6.3 (6.9)
% Total variance
Between-individual, %	91.3	82.4	86.7	88.9	90.7	93.5	89.9
Between-visit, %	8.5	17.1	13	10.9	9	6.3	9.9
Within-visit, %	0.2	0.4	0.3	0.2	0.2	0.2	0.2

SD: standard deviation; kg: kilograms; BMI: body mass index
${}^{\text{a}}$ P values$\mathrm{\hspace{0.17em}\hspace{0.17em}}>$  .70 for all F-tests comparing standard deviations within each group (e.g., for all participants, comparing SD of mean weight change at 30 months using a single day (6.3 kg) to that using 2 days (6.3 kg), $P\mathrm{\hspace{0.17em}\hspace{0.17em}}\text{value}=.98$).
${}^{\text{b}}$BMI 25–29.9 kg/m²
${}^{\text{c}}$BMI$\mathrm{\hspace{0.17em}\hspace{0.17em}}\ge \mathrm{\hspace{0.17em}\hspace{0.17em}}$30 kg/m²
${}^{\text{d}}$BMI $\ge \mathrm{\hspace{0.17em}\hspace{0.17em}}$25 kg/${\text{m}}^2.$