. Author manuscript; available in PMC: 2011 Nov 4.

Published in final edited form as: Obesity (Silver Spring). 2008 Feb;16(2):377–383. doi: 10.1038/oby.2007.32

Table 3.

Piecewise logistic regression primary model results^a

Study	Sample size	Parameter estimate	s.e.	95% CI (bootstrapped)
NHIS 1997
BMI slope (low)^b	19,727	−0.151	0.115	(−1.235, −0.017)
Knot 1^c		18.97	2.236	(16.45, 20.30)
BMI slope (mid)^b		0.041	0.093	(0.033, 0.049)
Knot 2		35.08	4.212	(32.74, 48.91)
BMI slope (high)^b		−0.003	0.019	(−0.061, 0.016)
NHIS 1998
BMI slope	17,355	0.027	0.004	(0.021, 0.032)
NHIS 1999
BMI slope (low)	16,704	−0.056	0.063	(−0.137, 0.015)
Knot		20.19	3.219	(18.83, 22.17)
BMI slope (high)		0.030	0.020	(0.025, 0.036)
NHIS 2000
BMI slope	17,298	0.034	0.003	(0.030, 0.039)
NHIS 2001
BMI slope	17,666	0.029	0.003	(0.024, 0.033)
NHIS 2002
BMI slope	16,280	0.031	0.004	(0.025, 0.036)
NHIS 2003
BMI slope (low)	16,230	−0.102	0.130	(−1.030, 0.020)
Knot		19.61	3.471	(18.04, 21.72)
BMI slope (high)		0.039	0.010	(0.033, 0.044)
ACHS
BMI slope (low)	3,647	−0.157	0.155	(−0.333, 0.018)
Knot		19.42	2.087	(18.21, 22.45)
BMI slope (high)		0.032	0.013	(0.010, 0.052)
TCHS^d
BMI slope	2,397	0.022	0.009	(0.005, 0.038)
NHANES I^e
BMI slope	10,113	0.013	0.012	(−0.016, 0.032)
WHI
BMI slope	82,953	0.000	0.002	(−0.004, 0.004)

Adjusted for age, race, and smoking status;

BMI was divided into 1, 2, or 3 contiguous segments (depending on the number of knots in the model—0, 1, or 2, respectively) and will have an estimate of the linear rate of change in log odds of headache per segment: low, mid, high;

Knots were entered into the model and retained only if they contributed significantly to model fit at significance level 0.05;

100% white;

Employment status for men only and not adjusted for smoking as nearly 60% of records are missing that data.