Table 5.

SPS Cox’s proportional hazards model results for variables predicting time-to-reoperation.

Variable	Estimate	Standard Error	Chi-Square	p-value	Hazard Ratio	95% Confidence interval (CI)
Age	−0.010	0.009	1.150	0.2835	0.99	0.97–1.01
Gender (Female vs Male)	−0.277	0.242	1.311	0.2523	0.76	0.47–1.22

Cox’s proportional hazards model was used to explore which variables maintained significance after adjusting for other variables in the model. Variables significant at p<0.10 were candidates for inclusion in the final multivariable regression model. Final selection for the model was done using the stepwise method as implemented in SAS Release 9.2 (SAS Institute, Cary, NC), which sequentially enters the most significant variable with p<0.10 and then after each entered variable removes variables that do not maintain significance at p<0.05. Age and gender were forced to be in the model.

Candidate predictor variables:

age, gender, race, education, marital status, work status, BMI, smoking status, work lift demand, hypertension, diabetes, osteoporosis, depression, heart problem, joint problem, time since most recent episode, patient’s self-assessment of health trend, patient dissatisfied with symptoms, expectation of free of pain with surgery, expectation of free of pain with nonoperative treatment, opioid use, injections, had physical therapy, taking antidepressants, taking NSAID, predominant back pain, low back pain bothersomeness scale, back pain bothersomeness scale, stenosis bothersomeness index, Oswestry disability index, bodily pain, physical function, mental component summary, physical component summary, neurogenic claudication, pain on straight-leg raising or femoral-nerve tension sign, dermatomal pain radiation, any neurologic deficit, asymmetric reflexe depression, asymmetric sensory decrease, asymmetric motor weakness, moderate or severe stenotic levels, location of stenosis, and severity of stenosis.