Table 2.

Results of multi-level cox regression models, with time as a constant variable, assessing the association between practice environment subscales and NP burnout (N = 396)

Modela	Practice environment subscale	Risk Ratio*	P > |z|	95% Confidence Interval
1	Professional Visibility	0.49	0.00	0.36	0.66
2	Independent Practice and Support	0.44	0.00	0.29	0.65
3	NP-Physician Relations	0.49	0.00	0.34	0.71
4	NP-Administration Relations	0.42	0.00	0.31	0.56

Note. NP = Nurse Practitioner;

^*Because we did not have NP responses recorded over various time points, we created a constant time variable. When there is a constant time variable in a multi-level cox regression model, the hazard ratio is the same as the risk ratio. Thus, we reported the risk ratio in this table; Four independent multi-level models were run, one for each practice environment subscale.

^aIn each model, we controlled for age, sex, race, education, marital status, workload, years of experience as an NP, average hours worked per week, practice size, hours of operation (nights and weekends), type of primary care practice, survey type, and state.