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J P Hoffmann

Publications and source records attributed to J P Hoffmann.

17 recordsLinked to original sources
PubMed2006

Analysis of a Schnute postulate-based unified growth model for model selection in evolutionary computations.

In order to evaluate the feasibility of a combined evolutionary algorithm-information theoretic approach to select the best model from a set of candidate invasive species models in ecology, and/or to evolve the most parsimonious model from a suite of competing models by comparing their relative performance, it is prudent to use a unified model that covers a myriad of situations. Using Schnute's postulates as a starting point [Schnute, J., 1981. A versatile growth model with statistically stable parameters, Can. J. Fish Aquat. Sci. 38, 1128-1140], we present a single, unified model for growth that can be successfully utilized for model selection in evolutionary computations. Depending on the parameter settings, the unified equation can describe several growth mechanisms. Such a generalized model mechanism, which encompasses a suite of competing models, can be successfully implemented in evolutionary computational algorithms to evolve the most parsimonious model that best fits ground truth data. We have done exactly this by testing the effectiveness of our reaction-diffusion-advection (RDA) model in an evolutionary computation model selection algorithm. The algorithm was validated (with success) against field data sets of the Zebra mussel invasion of Lake Champlain in the United States.

Algorithms↗
PubMed2000

A growth curve analysis of stress and adolescent drug use.

The purpose of this paper is to describe and examine one pathway by which adolescent drug use increases during early and mid-adolescence. It draws upon recent research on adolescent stress, drug use, and family processes to describe an important stage of the life course. A chief principle underlying the proposed pathway is that the cumulative effect of stressful life experiences over time can lead to a steeper escalation of drug use in adolescence. Furthermore, based on previous stress research, we propose that this effect may be moderated by factors such as sex, income, family attachment, self-esteem, and mastery. Using 4 years of panel data from the Family Health Study (n = 651 adolescents ages 11-14 during Year 1), we estimate a hierarchical growth curve model that examines the time-varying effects of stressful life events and peer relations on drug use. The results indicate that experiencing a high number of life events over time is related to a significant "growth" of drug use, even after controlling for "growth" due to age or peer relations. In addition, this relationship is moderated by family attachment; high levels of attachment serve to diminish this growth significantly.

Adolescent↗
PubMed2000

Adolescent cigarette smoking in U.S. racial/ethnic subgroups: findings from the National Education Longitudinal Study.

Using nationally representative data for 16,454 8th graders and 13,840 10th graders, we explore racial/ethnic differences in "daily cigarette initiation," beginning to smoke on a daily basis between baseline interviews and reinterviews conducted two years later. In both samples, the initiation rate among whites is more than double the rate among blacks and higher than rates among Asian/Pacific Islanders and Hispanics. Risk factors at the individual, family, and peer-group levels of analysis do not explain most racial/ethnic differences. We develop alternative hypotheses by extending theories of cigarette use to the school level, and we test them using multilevel models: Consistent with social learning theory, cigarette risk among blacks and Hispanics decreases as the percentage of racial/ethnic minority students in the school increases. Consistent with strain theory, cigarette risk increases with the academic competitiveness of the school--especially among females--after controlling for the adolescent's academic performance.

Adolescent↗
PubMed2000

Gender differences in sexual behaviors and factors associated with nonuse of condoms among homeless and runaway youths.

Few studies have examined gender-specific factors associated with the nonuse of condoms among homeless and runaway youths (HRYs)-a population at high risk for HIV infection. In this article, we evaluate these factors and explore gender differences in background experiences, psychosocial functioning, and risk behaviors among HRYs from four U.S. metropolitan areas. Of 879 sexually active HRYs sampled, approximately 70% reported unprotected sexual intercourse during a 6-month period, and nearly a quarter reported never using condoms in the same period. Among males and females, having only one sex partner in the previous 6 months had the strongest association with nonuse of condoms. Among males, nonuse was also associated with having ever caused pregnancy, frequent marijuana use, prior physical victimization, and low self-control and sociability. Among females, nonuse was associated with knowledge of HIV status, prior sexual victimization, low social support, and infrequent marijuana use. These findings highlight the ongoing need for HIV prevention services for HRYs. Implications for the scope and content of these services are discussed.

Adolescent↗
PubMed1998

Parental substance use disorder, mediating variables and adolescent drug use: a non-recursive model.

AIMS: To develop and test a non-recursive model that examines the effects of parental psychoactive substance use disorder (PSUD) on the reciprocal relationships among stressful life events, family attachment, peer drug use and adolescent drug use. DESIGN: A 3-year prospective cohort study followed adolescents from three types of families defined by a parental diagnosis of a psychiatric disorder. SETTING: A large metropolitan area in the upper Midwestern United States. PARTICIPANTS: Seven hundred and seventy-seven 10-16-year-old adolescents from three groups of families: 214 who resided in families in which a parent was diagnosed with PSUD, 181 who resided in families in which a parent was diagnosed with an affective disorder (but no co-morbid PSUD), and 382 who resided in families in which both parents were free of any diagnosable disorder. MEASUREMENTS: Psychiatric disorder was defined by the Structured Clinical Interview for DSM-III-R (SCID). Two follow-up interviews of adolescent respondents were used to measure stressful life events via the Junior High Life Experiences Survey, family attachment via FACES-III and a child-parent strain index, peer drug use, and two self-reported drug use scales designed to measure past-year alcohol use and illicit drug use (e.g. marijuana, cocaine, inhalants). FINDINGS: Nested structural equation models with latent variables revealed that adolescents from PSUD families were at heightened risk of stressful life events, peer drug use, attenuated family attachments and drug use during the first follow-up period. In turn, peer drug use was strongly associated with drug use during the second follow-up period. However, drug use during the first follow-up also led to greater peer drug use and attenuated family attachment during the second follow-up period. The findings support a non-recursive model describing relations among adolescent drug use, peer drug use and family attachment. CONCLUSIONS: Parental psychoactive substance use disorder puts adolescents at significant risk of becoming embedded in a cycle of drug use, associations with drug using peers, and poor family relations.

Adolescent↗
PubMed1998

Stressful life events and adolescent substance use and depression: conditional and gender differentiated effects.

Stressful life circumstances have myriad influences on human health and behavior. Early research focused on the variable distribution of stress and its effects by socioeconomic status, race, and gender. More recent research indicates that variation by age is also an important consideration. For example, adolescent reactions to stressful life events are often inconsistent with adult reactions to similar life situations and transitions. Moreover, since most studies assess only a single outcome--usually depression--they risk classification bias since analyses exclude other potential stress-related outcomes. This paper assesses the gender distinct effects of stressful life events on two outcomes among adolescents, substance use and depressive symptoms. The results of a second-order regression model indicate that life events affect female, but not male, depressive symptoms, especially when self-esteem is low or mastery is high. Furthermore, life events affect substance use when peer drug use is high, or when parental support is low, but this latter effect is limited to female adolescents.

Adolescent↗
PubMed1997

Changes in network characteristics and HIV risk behavior among injection drug users.

Studies indicate that HIV risk behaviors vary greatly among injection drug users (IDUs). The source of such variation is often ascribed to individual differences, but much of it is due to how IDUs are grouped into social networks. Nevertheless, given the turbulent and uncertain lives led by many IDUs, it would not be surprising if their social networks changed substantially over time. We used data from a study of the social networks of IDUs in Chicago and Washington, DC, to examine changes in individual behavior and network characteristics over time. The results indicated few changes in standard network measures, such as density of ties or network size, over time. However, specific network change measures, that is, indicators of movement into and out of networks, showed significant movement of network members over time. Moreover, movement of members into a network significantly predicted a higher likelihood of risky injection drug use over time. We suggest that these movements are indicative of a lack of a stable resource base among IDU networks.

Adolescent↗
PubMed1995

The effects of family structure and family relations on adolescent marijuana use.

The role of family structure in adolescence has been linked to a host of problem behaviors, including marijuana use. This paper investigates the relationship between family structure and marijuana use, and elaborates previous research by 1) exploring several intervening mechanisms that affect the relationship, and 2) examining the effects of a variety of family forms. Analyses of data from the National Youth Survey (1977-79) indicate that 1) a parental divorce or living with a stepparent decreases family attachment among adolescents; 2) attenuated family attachment and involvement increase the likelihood of associating with drug-using peers; and 3) less family involvement and increased associations with drug-using peers increase the probability of initiating marijuana use and elevate frequency of use.

Adolescent↗
PubMed1995

Human lymphocyte cDNA ordered library analyzed by 2D gel electrophoresis. 1. Pooling strategy and matching of gel patterns.

We have analyzed an ordered library of 4,608 cDNA clones from the CEM human leukemic cell line. The aim was to facilitate gene retrieval, to enable immediate access to cDNA clones and to provide information on the protein expression of the individual clones in a 2D gel readout. The matrix array of 24 x 16 x 12, each position of which contained lambda jacII phage from one plaque, enabled us to establish pools of clones along the three axes (24 pools of complexity 192 cloned entities, 16 pools of complexity 288 and 12 pools of complexity 384). The total cDNA complexity is here reduced to such a level that spots which in more complex gels served as landmark spots are not present in each pool, and thus cannot serve as landmarks anymore. The image analysis of such gels and especially the matching of spots is not reliable under these circumstances. In order to achieve reliable matching, additional samples were created, such that pools were co-electrophoresed according to a special concatenation scheme; these samples then contained over-lapping elements (e.g., pools 1 + 2 + 3 and 3 + 4 + 5 have at least those spots in common, which originate from pool 3). This approach turned out to be feasible and we have completed the matching of one half of the ordered library. Already from the present stage of analysis we have obtained valuable information on the cDNA library and on the distribution of clones in this library.

DNA, Complementary↗
PubMedDate not supplied

The historical shift in the perception of opiates: from medicine to social menace.

An examination of the origins of the laws prohibiting the use of opiates in the United States is provided. The primary focus is on how the development of these laws influenced a marked shift in the perception of opiates. Historically, opium and its derivatives have been perceived as efficacious medicines. However, during the past two centuries this perception has shifted to the point that contemporarily the opiates are commonly thought of as a social menace. This perception now outweighs the efficacious medicine perception to a substantial degree. A historical analysis indicates that this shift occurred not so much because the hazardous potential for addiction and overdose was discovered, nor because recreational use became widespread; rather, this shift was greatly influenced by underlying national economic conditions and concerns.

Asia↗