Table 3.

 Negative binomial regression output reporting independent variable effects on citations to articles aged 9 to 12 months

Coefficient	Incidence rate ratio (95% CI)	P value
Open access	0.95 (0.81 to 1.10)	0.484
Cover article	0.93 (0.52 to 1.64)	0.789
Press release	1.23 (0.50 to 3.05)	0.654
Self archived	0.90 (0.53 to 1.55)	0.716
Review article	1.34 (1.01 to 1.78)	0.041
Methods article	0.62 (0.37 to 1.06)	0.079
Any author from USA	1.17 (1.04 to 1.32)	0.007
No of authors*	1.13 (1.01 to 1.26)	0.030
No of references*	1.42 (1.17 to 1.72)	<0.001
Article length (pages)*	1.09 (0.86 to 1.38)	0.483
Journal impact factor*	1.39 (1.10 to 1.76)	0.006
Issue	1.26 (1.20 to 1.33)	<0.001

χ² _{12, 1607}=313.14, P<0.001, pseudo R²=0.06, α for dispersion 0.43 (95% confidence interval 0.35 to 0.54).

*Log transformed.