Table 3 Estimated Regression Coefficients (β) and 95% Confidence Intervals (CI) in Adjusted and Unadjusted Linear Regression Models of the Log-transformed Blood THC (ng/ml) on Log-transformed Oral Fluid THC (ng/ml) among Drivers with Non-zero THC Concentrations in either Blood or Oral Fluid, Continental United States, Nighttime Weekend and Daytime Friday, 2013–2014
|  | Model 1 (n = 500) | Model 2 (n = 478) | Model 3 (n = 472) |
|---|---|---|---|
β (95%CI) | β (95%CI) | β (95%CI) | |
Intercept | 0.14 (0.01, 0.26) | 0.00 (−0.17, 0.17) | −0.01 (−0.31, 0.28) |
Log of Oral Fluid THC Concentration (ng/ml) | 0.25 (0.22, 0.29) | 0.25 (0.21, 0.29) | 0.25 (0.22, 0.29) |
Blood Alcohol Concentration (ng/dl) | |||
 0 |  | Ref | Ref |
 1–39 |  | − 0.29 (− 0.77, 0.19) | − 0.22 (− 0.72, 0.28) |
 40+ |  | − 0.18 (− 0.60, 0.25) | − 0.15 (− 0.58, 0.27) |
Last time use of Marijuana | |||
 Over a year/Never |  | Ref | Ref |
 Over a Month |  | 0.15 (−0.13, 0.42) | 0.16 (−0.12, 0.44) |
 Past 2 days to a month |  | 0.22 (−0.01, 0.45) | 0.22 (−0.01, 0.46) |
 Past 24 Hours |  | 0.29 (0.08, 0.49) | 0.30 (0.10, 0.51) |
Age (years) | |||
 16–20 |  |  | Ref |
 21–34 |  |  | 0.05 (−0.17, 0.27) |
 35–54 |  |  | 0.06 (−0.20, 0.33) |
  ≥ 55 |  |  | −0.13 (− 0.56, 0.30) |
Gender (Male vs. Female) |  |  | −0.12 (− 0.29, 0.06) |
Race | |||
 Black |  |  | Ref |
 White |  |  | −0.03 (−0.21, 0.15) |
 Other Race |  |  | 0.27 (0.01, 0.52) |
R2 | 0.29 | 0.30 | 0.31 |