Longitudinal Associations Between Other‐Sex Friendships and Substance Use in Adolescence

The impact of the changes in the gender composition of friendship networks during early adolescence on substance use in late adolescence was examined. The hypothesis was that initial level and increase in the proportion of other‐sex friends in the network would be associated with higher levels of substance use among girls, but not among boys. Girls and boys (n=390) were interviewed annually from ages 12 to 18 (79% retention). For both boys and girls, initial level in the proportion of other‐sex friends predicted alcohol use in late adolescence, whereas it was predictive of drug use in girls only. Moreover, for girls only, a faster increase in the proportion of other‐sex friends in the network predicted later use of alcohol and drugs.     

Appeals to social norms as policy instruments to address consumption externalities

We consider appeals to social norms as a policy instrument to address consumption externalities. We explore whether appeals to social norms can be an efficient policy instrument and compare the efficiency of such appeals to the efficiency of taxation in addressing consumption externalities. We find that when the existing norm helps to shift consumption towards the socially optimal level of consumption, taxation welfare dominates appeals to social norms as a policy tool. While previous studies have found that economic instruments are superior to information in other contexts, we arrive at a different conclusion for situations where the norm shifts behavior away from what is socially optimal. In such cases appeals to social norms can be a better policy instrument than taxation.     

On Estimation and Tests of Time-Varying Effects in the Proportional Hazards Model

Abstract.  Cox's proportional hazards model is routinely used in many applied fields, some times, however, with too little emphasis on the fit of the model. In this paper, we suggest some new tests for investigating whether or not covariate effects vary with time. These tests are a natural and integrated part of an extended version of the Cox model. An important new feature of the suggested test is that time constancy for a specific covariate is examined in a model, where some effects of other covariates are allowed to vary with time and some are constant; thus making successive testing of time-dependency possible. The proposed techniques are illustrated with the well-known Mayo liver disease data, and a small simulation study investigates the finite sample properties of the tests.     

ACQUISITION AND DISSEMINATION OF INFORMATION IN IMPERFECTLY COMPETITIVE MARKETS

In imperfectly competitive markets, incentives for the acquisition and dissemination of information by prices is significantly affected by strategic considerations. Since prices reveal information, firms possessing market power may choose to set prices which are either biased or not adjusted to all available information so as to distort their information content. Even when information is costlessly available strategic considerations may lead firms to remain uninformed. These results are illustrated in a simple Stackelberg model with price-setting firms where the pricing game is preceded by an information acquisition game.     

Is there a trend towards global value chain specialization? — An examination of cross border sales of US foreign affiliates

In this study we discuss and empirically test the assertion that over the last two decades multinational enterprises' (MNEs') configuration of value-adding activities has shifted from a sparse and simple (host–home) international division of labor among the foreign affiliates to a more specialized and ‘advanced’ global value chain configuration in which MNEs locate fine-sliced parts of the value chain at the most efficient locations. Using data on trade flows of U.S. affiliates in 56 host countries between 1983 and 2003 we find some indications of a trend in the direction of global value chain specialization. In particular among US affiliates in developing countries the proportion of host–host, intra-firm trade has increased significantly during the observed period of time. Conversely, the proportion of host–home and inter-firm trade has diminished. We interpret this as indicating both value chain disaggregation (vertical specialization) and MNEs' systematic exploitation of factor cost differentials across countries. We also find that the absolute levels of all types of trade flows have increased. Hence, it is the relative, and not the absolute, changes in the trade flow patterns of US affiliates that gives credibility to the global value chain assertion.     

Intercourse debut age: poor resources, problem behavior, or romantic appeal? a population-based longitudinal study

The most important predictors of early intercourse debut are reported to be poor social resources and early developing problem behaviors. In this study we have a new, additional emphasis on variables related to self-concept and social acceptance. In a population-based longitudinal study, 1399 Norwegians were followed over a 7-year span. We analyzed data using multivariate Cox-regression techniques. Early intercourse debut was part of a broader spectrum of problem behaviors, including early alcohol intoxication and early-developing conduct problems. A new finding was that a positive self-concept in the domain of romantic appeal was also a strong predictor, but only for boys. We suggest that the findings may have important implications for prevention and more research should be conducted along this line.     

Racial disparity in Minnesota's child protection system

Minnesota has been recognized by several studies as a state with a significant amount of racial disparity in its child protection system. This study, using 2001 data from Minnesota's Social Services Information Service, was conducted to determine at which of the six decision points in Minnesota's child welfare system racial disparities are statistically significant. The authors employ a nested model to examine a child's journey through the Minnesota child protection system. Using binary logistic regression, they are able to determine the odds that a child belonging to a particular racial or ethnic group would progress to the next decision point.     

Targeted estimation of state occupation probabilities for the non-Markov illness-death model

We use semi-parametric efficiency theory to derive a class of estimators for the state occupation probabilities of the continuous-time irreversible illness-death model. We consider both the setting with and without additional baseline information available, where we impose no specific functional form on the intensity functions of the model. We show that any estimator in the class is asymptotically linear under suitable assumptions about the estimators of the intensity functions. In particular, the assumptions are weak enough to allow the use of data-adaptive methods, which is important for making the identifying assumption of coarsening at random plausible in realistic settings. We suggest a flexible method for estimating the transition intensity functions of the illness-death model based on penalized Poisson regression. We apply this method to estimate the nuisance parameters of an illness-death model in a simulation study and a real-world application.