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Re: Symptoms of anxiety and depression in childhood and use of MDMA: prospective, population based study
- Wenbin Liang (12 April 2006)
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Re: Re: Symptoms of anxiety and depression in childhood and use of MDMA: prospective, population based study
- Anja C Huizink, Jan van der Ende (15 April 2006)
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Confounders
- Kathleen I Kelly, Akeem Sule, Spr Addictions, akeemsule@hotmail.com Oxford (26 April 2006)
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Wenbin Liang, master candidate School of Public Health Curtin University of Technology
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Dear Editor, Here are some considerations on the survival analysis in this study[1]. As the drug was first available in 1985[1], so no subjects would be at risk before this time point—hazard function of “survival time”(h0(t)) itself for this period would be zero, and the hazard for all subjects would be zero regardless the characteristics of the subject. The onset of drug use was likely related to the age at which the “boys and girls” first went to dance parties or other occasions in which the drug was available, and the effect of age itself (not the time since born) on the onset of drug use was strong. Therefore it might be suitable to consider the survival time as the time between 1985 and the time of an event or 1997. Reference 1. Huizink, A.C., et al., Symptoms of anxiety and depression in childhood and use of MDMA: prospective, population based study. Bmj, 2006. 332(7545): p. 825-8. Competing interests: None declared |
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Anja C Huizink, Assistant Professor Erasmus MC, Dept. of Child and Adolescent Psychiatry, PO Box 2060, 3000 CB Rotterdam, Netherlands, Jan van der Ende
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Dear Editor, We thank Wenbin Liang for pointing out an alternative procedure to conduct survival analysis in our study. In our study, individuals came under observation when they were first assessed at ages 4-17 years in 1983. These left truncation survival times were accommodated in our Cox regression models. Therefore, survival time in our study is the time between 1983 and the event time. Furthermore, since the order of event times is more important than their exact values, we would expect to find similar results with our data when the procedure suggested by Wenbin Liang, who proposed to compute the survival time as the difference between 1985 and the event time, is applied. Anja Huizink and Jan van der Ende, on behalf of all authors Competing interests: None declared |
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Kathleen I Kelly, Spr Addictions Oxford, Akeem Sule, Spr Addictions, akeemsule@hotmail.com Oxford
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We wondered if the authors set out to investigate the association between symptoms of anxiety and depression in childhood and use of MDMA. Genetic vulnerability is a major risk factor for childhood illicit drug use(Merikangas K R et al. 1998).Furthermore,an association has been shown between parental illicit drug use and psychiatric disorders including depression.(Mayes,1995). However the authors did not gather information regarding parental illicit drug use.This is an important potential confounding factor,influencing both risk factors and outcome in this study. In addition, the "self-medication" hypothesis proposed by the authors for the use of MDMA has been made without investigating alcohol use in the sample. Merikangas K R el al 1998 Familial transmission of substance use disorders. Arch Gen Psychiatry.1998 Nov;55(11):964-5 Mayes LC 1995 Substance Abuse and Parenting. In: Bornstein MH,ed The Handbook of Parenting.Mahwah,NH:Erlbaum.Pp. 101-125 Competing interests: None declared |
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