. Author manuscript; available in PMC: 2012 Jul 1.

Published in final edited form as: Health Serv Outcomes Res Methodol. 2011 Jul 1;11(1-2):54–78. doi: 10.1007/s10742-011-0071-9

Table 2.

Cigarette Smoking Effects on OFC

Model	Probit Regression Coefficient	Odds Ratio [95% CI]	1st IV condition X² [df]	2nd IV condition X² [df]	Exogenous Cigarettes X² [1]
Cigarettes before Pregnancy
Probit	0.013^* (0.007) [0.005^*]	1.2^* [0.97,1.48]
CML-IV probit	0.100^* (0.029) [0.033^*]	4.16^** [1.06,8.0]	26.87^*** [8]	3.3 [7]; p=0.86	5.7^**
Cigarettes in the first trimester
Probit	0.020^* (0.011) [0.008^*]	1.21^* [0.98,1.52]
CML-IV probit	0.172^* (0.046) [0.057^*]	5.41^* [0.88,9.81]	15.54^** [6]	2.52 [5]; 0.77	5.31^**

Note: The models are based on a sample size of 856 observations. Standard errors of regression coefficients are in parentheses. The marginal effects of cigarettes, evaluated holding all model variables at their means, are listed in brackets under the regression coefficient column (the standard errors of the marginal effects are suppressed for simplicity but are available from the authors upon request). The 95% confidence bounds of the odds ratio estimates are in brackets. The first IV condition column reports a chisquare test of the joint significance of the instruments in the cigarettes function (degrees of freedom [df] in brackets). The second IV condition reports the over-identification chi-square test (df in brackets).

p < 0.1,

^**

p < 0.05,

^***

p < 0.01.