. Author manuscript; available in PMC: 2011 Mar 2.

Published in final edited form as: Curr Med Res Opin. 2010 Nov 18;27(1):55–62. doi: 10.1185/03007995.2010.535511

Table 2.

Results of regression models comparing untreated and early ZA-treated groups.

	Log of FUP: coefficient (SE) from multiple regression	Time to first SC: HR (95% CI) from Cox regression	No. of SCs: coefficient (SE) from Poisson regression
Age	−0.014 (0.003)^*	1.008 (0.997–1.019)	0.016 (0.006)^†
CCI score	−0.143 (0.033)^*	1.097 (0.974–1.235)	0.134 (0.066)^†
Docetaxel treatment	0.281 (0.118)^†	1.291 (0.911–1.830)	0.116 (0.207)
Early ZA treatment	0.251 (0.107)^†^a	0.463 (0.280–0.679)^‡	−0.399 (0.198)^†^b
Time × early ZA treatment^c	Not included	1.002 (1.001–1.003)^†	Not included

p<0.0001;

^†

p<0.05;

^‡

p<0.001.

Because the dependent variable is log-transformed follow-up duration, the exponential of this regression coefficient represents ratio of follow-up duration of the late ZA-treated group to that of the early ZA-treated group. The exponential of 0.251 is 1.285. Therefore, the early ZA-treated group had a follow-up duration about 28.5% longer than the untreated group.

In Poisson regression, the exponential of this regression coefficient represents the ratio of skeletal complications in the late ZA-treated group to those in the early ZA-treated group. The exponential of −0.399 is 0.671; therefore, the early ZA-treated group had about 33% fewer skeletal complications than the untreated group, after controlling for follow-up duration.

The interaction term between time and early ZA treatment was included only in the Cox regression model.

CCI, Charlson Comorbidity Index; CI, confidence interval; FUP, follow-up duration; HR, hazard ratio; SC, skeletal complications; SE, standard error; ZA, zoledronic acid.