6 Predictor Block one USA Region Southeast versus Northeast Midwest versus Northeast West versus Northeast Urbanicity 250 K–1 M versus Metro >1 M <250 K versus Metro >1 M Patient ZIP code area Program ZIP code area Block two Block three Age 30–43 versus 18–29 43–81 versus 18–29 Female Race/ethnicity Hispanic versus non-Hispanic white Black versus non-Hispanic white Other versus non-Hispanic white Employed Block four Pain a reason for treatment First methadone treatment Strong urge to use Severe withdrawal Prescription opioid use in past 30 days Heroin use in past 30 days .21 −.18 .30∗∗ −.08 .18∗∗ <.01 .30∗∗ .13∗∗ .01 .14∗∗ .03∗∗ .02∗∗ .26∗∗ −.33∗∗ 0.592∗∗ 0.354∗ −0.215 0.307∗∗ 0.521∗ 0.307∗∗ 0.036 −0.021 −0.107∗∗ −0.019 −0.344∗∗ −0.454∗∗ −0.109∗∗ 0.005 −0.011 0.004 <0.001 0.003 0.081∗∗ −0.031 Table 2: Multilevel model predicting patient travel distance to OTP. Zero-order correlation Regression coeﬃcient Journal of Environmental and Public Health 95% Conﬁdence interval Interval estimates for each predictor have been exponentiated and can be interpreted as how travel distance is multiplied given a one-unit change in the predictor (or a contrast between one level of a categorical predictor and the reference category for that predictor). For predictors with multiple categories (i.e., USA Region, Urbanicity, Age, and Race/Ethnicity), the zero-order correlation is the multiple correlation when log distance is regressed on dummy variables. ∗P < .05; ∗∗P < .01. the magnitude of the distance between these two values is modest. Consistent with this ﬁnding, that a shorter travel distance is associated with missing data, we found that patient characteristics associated with missing data on other variables were also associated with most of the variables that were correlated with shorter travel distance (older age, nonwhite ethnicity, unemployment, previous methadone treatment, no prescription opioid use, and heroin use). 4. Discussion and Summary 4.1. Summary of Findings. Although the median distance traveled to an OTP was 7 miles, a small minority of patients (6%) traveled more than 50 miles to their OTP. Program variables related to patient travel distance included USA region and urbanicity. Patients enrolling in programs located in the Southeast and Midwest traveled greater distances than patients enrolling in the Northeast and West. Patients enrolling in programs located in moderately or low populated counties traveled greater distances than patients enrolling in densely populated urban areas. Patient variables related to travel distance included age, race/ethnicity, and the type of opioid used in the month before enrollment. Younger patients traveled greater distances than older patients. Non-Hispanic white patients traveled greater distances than Hispanic, African American, and patients in other racial/ethnic groups. Patients using prescription opioids in the month before enrollment traveled greater distances than patients using heroin in the month before enrollment. SE 0.145 0.170 0.169 0.129 0.160 0.006 0.050 0.013 0.016 0.012 0.022 0.025 0.036 0.012 0.012 0.012 0.018 0.014 0.016 0.017 Lower 1.354 1.015 0.576 1.051 1.223 1.345 0.938 0.954 0.871 0.958 0.680 0.605 0.836 0.972 0.965 0.980 0.966 0.976 1.051 0.939 Est. 1.808 1.424 0.807 1.359 1.683 1.360 1.037 0.979 0.899 0.981 0.709 0.635 0.896 0.995 0.989 1.004 1.000 1.003 1.085 0.970 Upper 2.413 2.000 1.130 1.758 2.316 1.375 1.146 1.004 0.927 1.005 0.740 0.666 0.961 1.019 1.013 1.028 1.035 1.030 1.119 1.002