Association between psychiatric disorders and the progression of tobacco use behaviors.

OBJECTIVE: To examine the progression of tobacco use and the patterns of comorbidity of tobacco use and psychiatric disorders. METHOD: The authors conducted analyses of prospective and retrospective reports, collected from 1988 to 1998, of a sample of high- and low-risk youths identified on the basis of the presence or absence of a parental history of substance abuse or dependence. RESULTS: A parental history of substance use disorders was associated with regular tobacco use and nicotine dependence, but not with experimentation for all youths. Individual and composite psychiatric diagnoses were strongly associated with nicotine dependence, but not with regular use or experimentation. While the presence of an affective disorder and drug abuse/dependence generally increased the risk for co-occurring nicotine dependence, analyses based on the temporal onset of disorders showed that it was the initiation of alcohol or drug use that predicted the progression to nicotine dependence. For low-risk youths, oppositional defiant disorder was the single psychiatric risk factor that predicted the transition to nicotine dependence. CONCLUSIONS: This study adds to the accumulating evidence that has implicated comorbid psychiatric disorders in the etiology and subsequent course of nicotine dependence. In addition, family history may represent an important indicator of an increased risk for nicotine dependence.

Dynamic patterns of time use in adolescence.

Patterns of time use are tangible representations of individual identity and the meaning of age groups in the life course. How do young people allocate their time to multiple domains of involvement, including the school, workplace, family, and peer group? Drawing on longitudinal data from the Youth Development Study (N = 1,010), a person-centered analytic strategy was used to describe configurations of time use through the high school years. Over half of the students were engaged in many domains, although a substantial percentage of students focused their time on one or two domains outside the school. Students who were highly engaged in multiple domains tended to remain so across grade levels, whereas students focused on one or two domains frequently changed their commitments. Plans for school, grade point average, future orientations that emphasize marriage and good citizenship, and gender significantly predicted time-use patterns. These findings elucidate connections among school, work, and other contexts through the high school years.

Metabolic control and quality-of-life self-assessment in adolescents with IDDM.

OBJECTIVE: To examine the relation between metabolic control and self-assessed quality of life in adolescents with IDDM. RESEARCH DESIGN AND METHODS: The Diabetes Quality of Life (DQOL) questionnaire for youths was given to 69 subjects with IDDM aged 10-20 years at the time of their outpatient visit. Subjects with IDDM of < 1 year's duration or with documented psychotic disorder or mental retardation were excluded. Metabolic control was assessed by the mean HbA1c during the preceding year (long-term), by a single HbA1c at the time of the visit (short-term), and by the number of acute events related to IDDM in the preceding year. RESULTS: The DQOL score correlated with mean HbA1c (beta = 6.13, R2 = 0.22, P = 0.0122) and single HbA1c (beta = 3.94, R2 = 0.18, P = 0.05). Self-health assessment was the best predictor of DQOL score (beta = -44.42, R2 = 0.45, P < 0.0001). The Worries subscale score on DQOL correlated with the occurrence of acute events (beta = 6.97, R2 = 0.2, P = 0.006), but did not correlate with either HbA1c level. Correlations of mean HbA1c with the predictors were stronger than the correlations of single HbA1c with the same predictors. CONCLUSIONS: Metabolic control and quality of life are two important outcomes of IDDM care. In our study, adolescents in better metabolic control report better quality of life. Both components need to be addressed in developing successful diabetes treatment strategies for adolescents with IDDM.

An Alternative Framework for Defining Mediation.

The present article provides an alternative framework for evaluating mediated relationships. From this perspective. a mediated process is a chain reaction, beginning with an independent variable that affects a mediator that in turn affects an outcome. The definition of mediation offered here, presented for stage sequences, states three conditions for establishing mediation: (a) the independent variable affects the probability of the sequence no mediator to mediator to outcome; (b) the independent variable affects the probability of a transition into the mediator stage; (c) the mediator affects the probability of a transition into the outcome stage at every level of the independent variable. This definition of mediation is compared and contrasted with the well-known definition of mediation for continuous variables discussed in Baron and Kenny (1986), Judd and Kenny (1981), and Kenny, Kashy, and Bolger (1997). The definition presented in this article emphasizes the intraindividual, time-ordered nature of mediation.

Organizing principles for single-joint movements. IV. Implications for isometric contractions.

1. Normal human subjects made isometric pulse and step contractions about the elbow to visually defined target torques of different amplitudes and at different rates. We measured joint torque and electromyograms (EMG) from two agonist and two antagonist muscles. 2. When the task specification requires that the subject explicitly alter the rate at which torque is increased, the rates of rise of the agonist and antagonist EMG bursts covary with the rate of rise of the torque. For pulses of torque the duration of motoneuron excitation varies with the duration of the task-defined contractile event. 3. When a subject is asked to generate torques of different amplitudes without specifying a time interval, torque amplitude is positively correlated with how long, and therefore how high, the EMG rose. Subjects usually proportionately covary the strength of the agonist and antagonist contractions but are not constrained to do so. Some subjects use a strategy of varying the antagonist inversely with the agonist contraction. 4. We extend the organizing principles for the control of movement about a single joint to the control of isometric torque. These rules state that control of torque about a single joint is exercised by one of two strategies: the speed-sensitive strategy modulates the rate at which contraction rises by varying the intensity of motoneuron-pool excitation. The speed-insensitive strategy varies the duration over which contraction rises but does not change the rate. These two respective patterns of torque emerge from pulse-height and pulse-width modulation of motoneuron-pool excitation. 5. The rules defining speed-sensitive and speed-insensitive strategies for movements are broadened for isometric contractions because of the wider range of torque patterns that we observe under these conditions. We propose a step-excitation component for prolonged isometric step contractions and slowly rising ramp patterns of excitation for contractions that develop over several hundreds of milliseconds. 6. The choice of strategies is based on task-specific torque requirements. The same two strategies that control torque to produce movement apply to the control of isometric torque. Unlike movements, however, isometric tasks are more often controlled by a blending of the two patterns. Possible reasons for this are discussed.