Table 3.

 Univariable and multivariable associations between covariates and all cause mortality

Cohort characteristic	Unadjusted hazard ratio (95% CI)	Adjusted hazard ratio (95% CI)
Male sex	1.06 (0.77 to 1.45)	NA
Age (per year)	1.04 (1.02 to 1.05)*	1.00 (0.98 to 1.01)
Social class (Carstairs):
1 (reference category)	1.0	1.0
2	0.16 (0.04 to 0.73)*	0.18 (0.04 to 0.82)*
3	0.48 (0.16 to 1.40)	0.52 (0.17 to 1.54)
4	0.49 (0.16 to 1.49)	0.45 (0.15 to 1.41)
5	0.41 (0.14 to 1.17)	0.36 (0.12 to 1.04)
6	0.62 (0.22 to 1.70)	0.46 (0.16 to 1.28)
7	0.54 (0.19 to 1.51)	0.52 (0.18 to 1.76)
Comorbidity (Charlson index):
0 (reference category)	1.0	1.0
1-2	2.85 (1.86 to 4.37)*	1.08 (1.02 to 1.14)*†
≥3	6.58 (4.72 to 9.19)*	1.20 (1.15 to 1.26)*†
Mean methadone dose ≥60 mg	1.54 (1.07 to 2.23)*	0.93 (0.62 to 1.39)
Overusing methadone	3.12 (2.09 to 4.64)*	1.67 (1.05 to 2.67)*
Methadone breaks	0.58 (0.50 to 0.67)*	0.93 (0.78 to 1.10)
Duration of methadone treatment (years)	0.78 (0.75 to 0.82)*	0.95 (0.94 to 0.96)*†
Time since last methadone prescription filled (months):
≤1 (reference category)	1.0	1.0
2-3	0.77 (0.49 to 1.22)	0.97 (0.91 to 1.02) †
4-6	0.66 (0.33 to 0.1.30)	0.91 (0.84 to 0.99)* †
>6	0.45 (0.32 to 0.62)*	0.70 (0.66 to 0.73)* †
Psychiatric admission	2.46 (1.74 to 3.49)*	2.47 (1.67 to 3.66)*
Having urine tested	0.31 (0.23 to 0.41)*	0.33 (0.22 to 0.49)*
Co-prescribing:
Benzodiazepines	1.18 (0.74 to 1.86)	NA
Antipsychotics	0.77 (0.53 to 1.12)	0.85 (0.56 to 1.29)
Antidepressants	0.76 (0.56 to 1.01)	0.80 (0.57 to 1.44)
Opioid analgesics	1.33 (0.99 to 1.79)	1.17 (0.84 to 1.64)

Final regression model mutually adjusted for all significant covariates; male sex, use of benzodiazepines, and volume of methadone prescribing by practice were assessed unadjusted but had no significant influence (P>0.2) and so were excluded from final model.

NA=not applicable.

*P<0.05.

†Variable treated as time varying coefficient in Cox regression model and hazard ratio reported at median follow-up of 4.38 years.