Table 1.

Mean and SD of BMI difference by survey year, BMI categories, and socio-demographic characteristics ^a

Characteristic	N	Mean and SD of BMI difference					Test for trends b
		1999–2000	2001–2002	2003–2004	2005–2006	2007–2008	p value
Overall	18 394	0.55	0.49	0.46	0.56	0.57	0.467
		(1.847)	(1.984)	(1.664)	(1.770)	(1.734)	0.132
Sex
Male	9 373	0.31	0.22	0.31	0.42	0.36	0.052
		(1.528)	(2.014)	(1.494)	(1.718)	(1.595)	0.635
Female	9 021	0.80	0.75	0.61	0.69	0.77	0.601
		(2.088)	(1.917)	(1.803)	(1.811)	(1.837)	0.082
Race/ethnicity
Non-Hispanic White	10 000	0.60	0.49	0.46	0.56	0.59	0.683
		(1.590)	(1.844)	(1.515)	(1.629)	(1.570)	0.426
Non-Hispanic Black	4 312	0.44	0.53	0.51	0.56	0.52	0.522
		(2.497)	(2.197)	(2.210)	(2.293)	(2.175)	0.239
Mexican American	4 082	0.25	0.36	0.34	0.51	0.42	0.115
		(2.975)	(2.888)	(2.064)	(2.157)	(2.283)	0.050
Age
20–39	6 232	0.46	0.39	0.43	0.42	0.48	0.745
		(1.813)	(2.331)	(1.703)	(1.821)	(1.801)	0.259
40–59	6 218	0.48	0.43	0.41	0.59	0.53	0.130
		(1.979)	(1.797)	(1.709)	(1.838)	(1.701)	0.261
60–89	5 944	0.85	0.81	0.62	0.74	0.82	0.511
		(1.645)	(1.513)	(1.486)	(1.505)	(1.641)	0.941
BMI categories
BMI < 30	12 110	0.25	0.18	0.15	0.21	0.21	0.688
		(1.475)	(1.685)	(1.248)	(1.301)	(1.287)	0.052
BMI ≥30	6 284	1.26	1.18	1.11	1.23	1.27	0.690
		(2.364)	(2.387)	(2.163)	(2.278)	(2.207)	0.322

^aStandard deviations (SD) are presented in parentheses. Observations are weighted to be nationally representative of the U.S. population.

^bTest results of trends in BMI difference are based on simple liner regression models regressing BMI difference on survey year. Test results of trends in the standard deviation are based on simple linear regression models regressing squared residuals on survey year.