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Francis SARTOR Scientific Institute of Public Health Epidemiology Unit Brussels, Belgium Reconstructing incidence of heroin use from treatment data

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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 Background

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Statistical method Principle Characteristics of treatment data used to calculate latency time (survival techniques) Random sample (representative) Effect of incomplete observation o Left & right truncation o Left censoring Use of treatment data collected in a sample of 15 centres in the French Community ( ) Reconstructing incidence curves using RDA : contents

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Statistical method

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E x : adjusted (expected) incidence at time X O x : 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 Principle of the RDA

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Truncation & censoring

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Right & left truncation

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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, Cumulated frequency distribution of latency period

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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 Cumulated frequency distribution of latency period

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* used as a random sample of heroin users ** used in survival analyses with right truncated data Sample of heroin users (n=2265) First treatment demand Missing latency period % > 30 years old % Latency period > 11 yrs * % Starting use : ** %

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Results

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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 Conclusions

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