Table 1.
Estimated size of the population of people who inject drugs (PWID) in Bristol in 2011: assessment of sensitivity of results to exclusion of CJIT referrals and/or non‐incident cases in the treatment list. Estimated interaction terms from each model are shown in the Appendix, Supporting information.
| Log‐linear model | Choice of treatment list (total number of PWID observed in CRC data set) | |||||||
|---|---|---|---|---|---|---|---|---|
| A: Full list including CJIT referrals (2450) | B: Full list excluding CJIT referrals (2418) | C: Incident list including CJIT referrals (1089) | D: Incident list excluding CJIT referrals (1066) | |||||
| Estimated population size (95% CI) | AIC | Estimated population size (95% CI) | AIC | Estimated population size (95% CI) | AIC | Estimated population size (95% CI) | AIC | |
| (1) No interactions | 3080 (2980, 3210) | 162 | 3330 (3190, 3500) | 100 | 1910 (1780, 2070) | 90 | 2350 (2140, 2600) | 57 |
| (2) T×N | 2740 (2670, 2840) | 93 | 3050 (2920, 3210) | 76 | 1790 (1660, 1950) | 84 | 2380 (2120, 2700) | 59 |
| (3) T×C | 4000 (3670, 4420) | 70 | 3970 (3640, 4390) | 70 | 2490 (2180, 2890) | 58 | 2470 (2150, 2870) | 58 |
| (4) N×C | 3100 (2990, 3230) | 162 | 3370 (3220, 3540) | 97 | 1840 (1710, 1990) | 86 | 2320 (2090, 2600) | 59 |
| (5) T×N + T×C | 4510 (3090, 9150) | 72 | 3750 (3080, 5120) | 72 | 2920 (2230, 4030) | 58 | 2770 (2210, 3620) | 58 |
| (6) T×N + N×C | 2740 (2670, 2840) | 95 | 3070 (2930, 3240) | 76 | 1680 (1560, 1830) | 76 | 2340 (2060, 2720) | 61 |
| (7) T×C + N×C | 4260 (3850, 4790) | 59 | 4230 (3810, 4760) | 60 | 2490 (2110, 3010) | 60 | 2460 (2080, 2980) | 60 |
| (8) T×N + T×C + N×C | 6890 (3740, 17680) | 59 | 5320 (3720, 8900) | 60 | 3540 (2320, 5930) | 59 | 3670 (2350, 6340) | 59 |
| (9) T×N + T×C + T×N×C | 4510 (3090, 9150) | 59 | 3750 (3080, 5120) | 60 | 2920 (2230, 4030) | 59 | 2770 (2210, 3620) | 59 |
| (10) T×N + N×C + T×N×C | 2740 (2670, 2840) | 59 | 3070 (2930, 3240) | 60 | 1680 (1560, 1830) | 59 | 2340 (2060, 2720) | 59 |
| (11) T×C + N×C + T×N×C | 4260 (3850, 4790) | 59 | 4230 (3810, 4760) | 60 | 2490 (2110, 3010) | 59 | 2460 (2080, 2980) | 59 |
T = Treatment, N = needle exchange, C = Criminal Justice Intervention Team; e.g. ‘T×N’ refers to a treatment by needle exchange interaction term in the log‐linear model. AIC = Akaike information criterion. AIC values should be compared within columns only. Estimates from models with the lowest AIC for each data set are shaded. CRC = capture–recapture; CJIT = Criminal Justice Intervention Team; PWID = people who inject drugs; CI = confidence interval.