Appendix Table 2.
Parameter Estimates From a Classical Logistic Regression Model With Lowest AIC Statistic for Injecting Drug Users, England and Wales, 1992–2006
| Parameter | Estimate | Standard Error | z Value | P Value |
| Intercept | −0.105 | 0.058 | −1.82 | 0.069 |
| Year of test | ||||
| Linear | 0.081 | 0.012 | 6.57 | <0.001 |
| Quadratic | 0.0045 | 0.0022 | 2.05 | 0.041 |
| Cubic | −0.00112 | 0.00026 | −4.38 | <0.001 |
| Age, years | ||||
| Linear | 0.0124 | 0.0066 | 1.87 | 0.061 |
| Quadratic | −0.00069 | 0.00027 | −2.52 | 0.012 |
| Gender, females | 0.262 | 0.085 | 3.07 | 0.002 |
| Injecting duration, years | ||||
| Linear | 0.1131 | 0.0072 | 15.79 | <0.001 |
| Quadratic | −0.00394 | 0.00061 | −6.48 | <0.001 |
| Cubic | 0.000061 | 0.000025 | 2.43 | 0.015 |
| Region, baseline London | ||||
| Midlands and Wales | −0.593 | 0.085 | −6.97 | <0.001 |
| North East and Yorkshire | −0.713 | 0.095 | −7.54 | <0.001 |
| North West | 0.404 | 0.069 | 5.83 | <0.001 |
| Southern and Eastern | −0.876 | 0.070 | −12.42 | <0.001 |
| Gender × injecting duration | ||||
| Females × linear effect | −0.0169 | 0.0080 | −2.13 | 0.033 |
| Females × quadratic effect | −0.0036 | 0.0012 | −3.12 | 0.002 |
| Females × cubic effect | 0.000190 | 0.000063 | 2.99 | 0.003 |
| Injecting duration × region | ||||
| Linear × Midlands and Wales | −0.014 | 0.010 | −1.35 | 0.178 |
| Linear × North East and Yorkshire | 0.039 | 0.013 | 2.97 | 0.003 |
| Linear × North West | −0.0230 | 0.0082 | −2.79 | 0.005 |
| Linear × Southern and Eastern | 0.0064 | 0.0078 | 0.83 | 0.409 |
| Year of test × injecting duration | ||||
| Linear × linear | −0.00142 | 0.00075 | −1.91 | 0.057 |
| Quadratic × linear | −0.00084 | 0.00017 | −5.02 | <0.001 |
| Linear × quadratic | 0.000110 | 0.000061 | 1.82 | 0.069 |
| Quadratic × quadratic | 0.000028 | 0.000014 | 1.98 | 0.048 |
| Year of test × region | ||||
| Linear × Midlands and Wales | −0.039 | 0.015 | −2.63 | 0.009 |
| Linear × North East and Yorkshire | −0.057 | 0.025 | −2.29 | 0.022 |
| Linear × North West | −0.000 | 0.012 | −0.00 | 0.999 |
| Linear × Southern and Eastern | −0.055 | 0.011 | −4.91 | <0.001 |
| Quadratic × Midlands and Wales | −0.0045 | 0.0033 | −1.35 | 0.177 |
| Quadratic × North East and Yorkshire | −0.0043 | 0.0052 | −0.82 | 0.413 |
| Quadratic × North West | −0.0036 | 0.0026 | −1.39 | 0.164 |
| Quadratic × Southern and Eastern | 0.0046 | 0.0026 | 1.75 | 0.079 |
| Age × region | ||||
| Linear × Midlands and Wales | 0.025 | 0.011 | 2.40 | 0.017 |
| Linear × North East and Yorkshire | −0.002 | 0.012 | −0.20 | 0.841 |
| Linear × North West | 0.0268 | 0.0084 | 3.17 | 0.002 |
| Linear × Southern and Eastern | 0.0381 | 0.0082 | 4.63 | <0.001 |
| Gender × region | ||||
| Females × Midlands and Wales | −0.16 | 0.13 | −1.19 | 0.233 |
| Females × North East and Yorkshire | 0.04 | 0.15 | 0.28 | 0.777 |
| Females × North West | −0.01 | 0.10 | −0.13 | 0.894 |
| Females × Southern and Eastern | 0.25 | 0.10 | 2.49 | 0.013 |
Abbreviation: AIC, Akaike Information Criterion.