TABLE 3.

List of predictors and their descriptions

Predictor	Variable type	Description
Age	Continuous	In years at the time of visit
Diagnosis subgroup	Categorical	I (reference), II, III or IV
Age × subgroup	Interaction	Age at subgroup II
	Interaction	Age at subgroup III
	Interaction	Age at subgroup IV
	Interaction	Age at subgroup other
Sex	Binary	Female versus male
First LBP is PCP or not	Binary	Yes versus no
Charlson score	Continuous	Comorbidity score
Time interval	Continuous	Number of months between first and second LBP visit
Smoking	Binary	Missing versus no
	Binary	Quit versus no
	Binary	Yes versus no
Alcohol	Binary	Missing versus no
	Binary	Yes versus no
Number of opioid prescriptions before LBP	Count	Number of opioid prescriptions before first LBP visit
First LBP visit is ED	Binary	Yes versus no
CT order at first LBP	Binary	Yes versus no
MRI order at first LBP	Binary	Yes versus no
Other image at first LBP	Binary	Yes versus no
Injection order at first LBP	Binary	Yes versus no
Med order at first LBP	Binary	Yes versus no
Lab order at first LBP	Binary	Yes versus no
Number of visits before LBP	Count	Number of visits for any reason before first LBP visit
Depression	Binary	Level 2 versus level 1
	Binary	Level 3 versus level 1
	Binary	Level 4 versus level 1
	Binary	Level 5 versus level 1
Allergic rhinitis	Binary	Yes versus no
Arthritis	Binary	Yes versus no
Beta-blocker and HT	Binary	Beta-blocker order not for HT versus no beta-blocker, no HT
	Binary	HT without beta-blocker versus no beta-blocker, no HT
	Binary	Beta-blocker for HT versus no beta-blocker, no HT
Physician efficiency index (/1000)	Continuous	See Data and Methods section for detail
Medicare	Binary	Yes versus no
Workers’ compensation	Binary	Yes versus no
Commercially insured	Binary	Yes versus no

CT Computed tomography; ED Emergency department; HT Hypertension; Lab Laboratory; LBP Low back pain; Med Medical; MRI Magnetic resonance imaging; PCP Primary care physician