Table 2.

Estimation results of negative binomial models

	Model 1		Model 2		Model 3
Coefficient (SD)	Odds ratio (SD)	Coefficient (SD)	Odds ratio (SD)	Coefficient (SD)	Odds ratio (SD)
Union	0.604 (0.036)	1.830 (0.066)	0.595 (0.036)	1.812 (0.065)	0.569 (0.036)	1.767 (0.063)
Hscommittee1	−0.134 (0.038)	0.874 (0.033)	−0.115 (0.038)	0.891 (0.033)	−0.149 (0.038)	0.862 (0.033)
Hscommittee2	−0.222 (0.063)	0.801 (0.051)	−0.122* (0.062)	0.885* (0.055)	−0.151 (0.062)	0.860 (0.054)
Ln(emp)	0.667 (0.010)	1.948 (0.020)	0.678 (0.010)	1.970 (0.021)	0.671 (0.010)	1.956 (0.020)
Office			−0.238 (0.042)	−0.238 (0.042)	−0.279 (0.042)	0.757 (0.032)
Female			−1.025 (0.041)	0.359 (0.015)	−0.977 (0.041)	0.377 (0.015)
Older			0.460 (0.054)	1.584 (0.086)	0.461 (0.054)	1.586 (0.086)
Foreign			1.229 (0.046)	3.418 (0.158)	1.159 (0.047)	3.187 (0.148)
Weekhr			–	–	0.098 (0.016)	1.103 (0.017)
Salesperwrk			–	–	0.132 (0.014	1.000 (0.000)
Constant	−3.674 (0.031)	0.025 (0.001)	−3.575 (0.038)	0.028 (0.001)	−3.789 (0.051)	0.023 (0.001)
Alpha (α)		1.990 (0.040)		1.767 (0.037)		1.746 (0.037)
Log-likelihood		−59,508.5		−58,716.9		−58,421.1
Test of alpha (α) = 0		${\overline{\chi }}_{\left(01\right)}^2$ = 1.2 × 104p < 0.001		${\overline{\chi }}_{\left(01\right)}^2$ = 1.0 × 104p < 0.001		${\overline{\chi }}_{\left(01\right)}^2$ = 1.0 × 104p < 0.001
Number of observations		3,000		3,000		2,967

Estimation is done by the maximum likelihood method using the sample weights. Likelihood ratio tests suggest that negative binomial models are better than Poisson models.

* Not significant at the 5% level.

SD, standard deviation.