Table 4.

Proportional hazard model for time until study discontinuation

Maximum likelihood estimates
Variable	DF	Parameter estimate	Standard error	Chi-square	P value	Hazard ratio
Treatment groupa	1	−0.30780	0.22998	1.7912	0.1808	0.735
Crossoverb	1	0.84766	0.41430	4.1862	0.0408	2.334
APACHE IIc	1	−0.00684	0.03042	0.0506	0.8221	0.993
Depressiona	1	−0.03805	0.01773	4.6059	0.0319	0.963
Pain intensityb	1	0.04402	0.04599	0.9165	0.3384	1.045
Pain unpleasantnessb	1	−0.05507	0.05577	0.9751	0.3234	0.946
Symptom distressb	1	0.06457	0.01579	16.7151	<.0001	1.067

^aAt baseline (preop),

^btime-varying covariate,

^cwithin 24 h postop