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OBJECTIVES. Prior research has identified developmental stages in drug use in adolescence, from substances that are legal for adults to illicit drugs. The position of crack in patterns of drug involvement remains to be established. METHODS. The analyses are based on a sample (n = 1108) representative of 12th graders attending New York State public and private schools. From reported ages of first use of five classes of drugs (alcoholic beverages, cigarettes, marijuana, cocaine but not crack, crack), alternate models of progression were tested for their goodness of fit through log-linear models. RESULTS. The sequence involves at the earliest stage the use of at least one licit drug, alcohol or cigarettes. Subsequent stages involve marijuana and cocaine; crack is the last drug in the sequence. The results confirm the more important role of alcohol among males and cigarettes among females in the progression into various drug classes. Age of first drug use at a lower stage is a strong predictor of further progression. CONCLUSIONS. The developmental pattern of drug involvement identified in the early 1970s still characterizes adolescent pathways of drug involvement in the late 1980s.

Abstract. In this paper we propose a slanted plane model for jointly recovering an image segmentation, a dense depth estimate as well as boundary labels (such as occlusion boundaries) from a static scene given two frames of a stereo pair captured from a moving vehicle. Towards this goal we propose a new optimization algorithm for our SLIC-like objective which preserves connecteness of image segments and exploits shape regularization in the form of boundary length. We demonstrate the performance of our approach in the challenging stereo and flow KITTI benchmarks and show superior results to the state-of-the-art. Importantly, these results can be achieved an order of magnitude faster than competing approaches.

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Possible linkages of influence among classes of drugs in the observed sequential progression from adolescence to young adulthood are investigated through event history analyses. Three stages are examined: initiation to marijuana, to the use of other illicit drugs, and to prescribed psychoactive drugs. The data are based on a follow-up cohort of former adolescents representative of high school students in grade 10 and 11 in New York State who were reinterviewed nine years later at ages 24-25. The sequential order between alcohol and/or cigarettes and marijuana reflects not only the effect of the use of legal drugs on marijuana initiation, but also age effects on onset of these drugs, controlling for individual characteristics measured in adolescence; marijuana use by one's IntroductionClear temporal developmental stages in the use of licit, illicit, and medically prescribed psychoactive drugs from adolescence through young adulthood have been identified, as reported in the second article in this series in this issue of the Journal.' For men, the pattern of progression is one in which alcohol precedes marijuana; alcohol and marijuana precede other illicit drugs; and alcohol, cigarettes, and marijuana precede the use of prescribed psychoactive drugs. For women, either alcohol or cigarettes precedes marijuana; alcohol, cigarettes, and marijuana precede other illicit drugs; alcohol and either cigarettes or marijuana precede prescribed psychoactive drugs. However, the sequential progression may reflect the relationships between the use of certain drugs and age and/or individual attributes rather than the specific effect of the use of one class of drug on the use of another.In this paper, we address the question of whether the use of certain drugs lower in the sequence influences the initiation of higher drugs through event history analysis. If the statistical effect of the use of an antecedent drug on initiation of a subsequent drug persists when other antecedent variables which could potentially explain initiation of the later drug are controlled, the earlier drug can be assumed to constitute a risk factor for progression. The independent variables being introduced as controls include-in addition to drug behaviors and age-selected antecedent individual behaviors, attitudes, and interpersonal factors found in our own earlier work carried out while respondents were adolescents,2-4 and in other studies,5-'4 to be the most important correlates of drug use at one point in time and the most important predictors of initiation into different drugs over a short time interval.

Anionic polymerization of 4-(tert-butyldimethyIsilyloxy)styrene (2) was investigated under high vacuum conditions mbar). 2 was readily polymerized by lithium naphthalide to form a "living polymer" at -78 "C. By subsequent acid hydrolysis of the resulting polymer, a linear, nearly monodisperse polymer of 4-vinylphenol of known molecular weight was obtained. Block copolymers of 2 with a-methylstyrene were also prepared by means of this living system.

Major pathways of progression among legal, illegal. and medically prescribed psychoactive drugs from adolescence to young adulthood are described. The data are based on a follow-up cohort of former adolescents representative of high school students in grades 10 and 11 in New York State who were reinterviewed nine years later at ages 24-25. Various models of progression are tested for their goodness of fit. The patterns formerly observed in adoles- IntrodiuctionStages of involvement in legal and illegal drugs have been described for adolescents. Adolescents are very unlikely to experiment with marijuana without prior experimentation with one of the alcoholic beverages or with cigarettes; very few try illicit drugs other than marijuana without prior use of marijuana, as documented in particular by our own earlier work-5 and the work of Jessor,/ O'Donnell and his colleagues,7-"' Johnston,'" Huba and Bentler,'2-'5 and others. '6'-To date, the empirical support for the concept of stages in drug use derives from cross-sectional data'0'2" 18 or from a short-term longitudinal follow-up.' 3 No results have been reported that are based on a follow-up of young people over several years with a detailed monitoring of their drug behavior past the period of risk for initiation into the relevant drugs. Such data are presented in this paper for a cohort of former high school students who were followed into young adulthood, at ages 24 to 25. By that age, the period of risk for initiation to the legal drugs, to marijuana, and to most other illicit drugs, with the exception of cocaine, is over, as reported in the first article of this series in this issue of the Journal.22In investigating pathways of progression among drugs, we address two related issues: I) whether the pattern of progression observed in adolescence over a short-term interval-i.e., from the use of at least one class of licit drug (alcohol or cigarettes), to the use of marijuana, to the use of other illicit drugs including the non-medical use of drugs available by prescription-holds when the same cohort of individuals is followed to young adulthood; and 2) whether the use of medically prescribed psychotropic drugs can be characterized as a later stage of progression. Methods Samples and Field ProceduresThe analyses are based on a follow-up in [1980][1981] The data were obtained through personal household interviews that took an average of two hours to administer. The interview schedule consisted almost exclusively of structured items with closed response alternatives.Analytical Strategies: Modified Guttman Scaling Five drug classes were distinguished: 1) alcohol, including beer, wine or distilled spirits; 2) cigarettes; 3) marijuana, including hashish; 4) other illicit drugs, including psychedelics, cocaine, heroin and non-prescribed use of stimulants, sedatives, minor tranquilizers, major tranquilizers, antidepressants, and methadone; and 5) prescribed psychotropic drugs, including minor tranquilizers, sedatives, and stimulants.Analyses of progression w...