Table 6. PWID prevalence trend analysis with linear, quadratic and cubic models of time.

	Model 1	Model 2	Model 3
Intercept	109.58**	107.08**	107.27**
Linear (years since 2000	−1.37**	−1.25**	−0.89**
Quadratic (years since 2000 squared)	–	0.20**	0.10**
Cubic (years since 2000 cubed)	–	–	−0.01

^**pseudo-p<0.001;

^*pseudo-p<0.05.

Note: To minimize potential multicollinearity time is centered at the year 2000. Model 3 is the best model by likelihood ratio test.