. Author manuscript; available in PMC: 2016 Mar 9.

Published in final edited form as: Int J Obes (Lond). 2010 Aug 17;35(2):300–308. doi: 10.1038/ijo.2010.137

Table 5.

Observational and instrumental variable derived relationships between BMI and circulating CRP.

Effect estimates
Outcome/explanatory variable	Observational	Instrumental variable	P _IV	P _diff	F _first
CRP/BMI	1.46 (1.44, 1.48)	1.41 (1.10, 1.80)	0.006	0.8	31.1
BMI/CRP	1.03 (1.00, 1.07)	−0.24 (−0.58, 0.11)	0.2	<0.0001	57.3

Observational analysis effects (95%CI) derived from linear regression adjusted for sex, age, age-squared, age–sex interaction, log(height), smoking, drinking, education and income.

CRP is log transformed for analyses above and effects on CRP are shown as ratios of geometric means for a standard deviation increase in BMI.

BMI effects are expressed as kg/m² for a doubling in logCRP.

Instrumental variable derived estimates of the same effects include the same covariates.

P_IV is the p-value from a test that the instrumental variable estimate is equal to the null.

P_diff is the p-value from a test for difference between the observational and instrumental variable estimates.

F_first is the first stage F-statistic from instrumental variable analysis.