140 likes | 225 Views
Reconstructing incidence of heroin use from treatment data. Francis SARTOR Scientific Institute of Public Health Epidemiology Unit Brussels, Belgium. Background. Collaborative study IPH-Biostatistical Unit at the University of Liège (Prof. A. Albert) aiming to investigate :
E N D
Reconstructing incidence of heroin use from treatment data Francis SARTOR Scientific Institute of Public Health Epidemiology Unit Brussels, Belgium
Background • Collaborative study IPH-Biostatistical Unit at the University of Liège (Prof. A. Albert) aiming to investigate : • A compartment model for epidemic of drug addiction • Incidence curve of heroin use applied to Belgian data • Funded by Federal Public Service of Public Health • Local continuation of one of the TSER projects • Final report expected by end Augustus
Reconstructing incidence curves using RDA : contents • Statistical method • Principle • Characteristics of treatment data used to calculate latency time (survival techniques) • Random sample (representative) • Effect of incomplete observation • Left & right truncation • Left censoring • Use of treatment data collected in a sample of 15 centres in the French Community(1993-98)
Principle of the RDA • Ex : adjusted (expected) incidence at time X • Ox : observed incidence at time X • F(x*-X) : cumulated frequency distribution of latency period (i.e the probability that an individual starting heroin use at time X demands a treatment for the first time not later than x*) can be estimated via survival analyses techniques
Cumulated frequency distribution of latency period • Ignore truncation problems : random sample assumption empirical cumulated distribution • Only right truncated data : adapted life table techniques* can be used to estimate the conditional cumulated distribution *Lagakos et al, 1988; Kalfleish & Lawless, 1989.
Cumulated frequency distribution of latency period • More difficult when data are both left & right truncated • Left censoring could be taken into account if unknown date at first use is known to have occurred before the start of the observation
Sample of heroin users (n=2265) * used as a random sample of heroin users ** used in survival analyses with right truncated data
Conclusions • Need of individual data on treatment demands • Random sample vs right/left truncation sample size may considerably • but, comparable adjustement by the 2 methods • need for comparisons in other countries/regions • Extended period of observation if epidemic peak closed to end of observation period • Effect on estimate of left censored & missing data should be studied