Sampling Strategies for Evaluating the Rate of Adventitious Transgene Presence in Non‐Genetically Modified Crop Fields

According to E.U. regulations, the maximum allowable rate of adventitious transgene presence in non‐genetically modified (GM) crops is 0.9%. We compared four sampling methods for the detection of transgenic material in agricultural non‐GM maize fields: random sampling, stratified sampling, random sampling + ratio reweighting, random sampling + regression reweighting. Random sampling involves simply sampling maize grains from different locations selected at random from the field concerned. The stratified and reweighting sampling methods make use of an auxiliary variable corresponding to the output of a gene‐flow model (a zero‐inflated Poisson model) simulating cross‐pollination as a function of wind speed, wind direction, and distance to the closest GM maize field. With the stratified sampling method, an auxiliary variable is used to define several strata with contrasting transgene presence rates, and grains are then sampled at random from each stratum. With the two methods involving reweighting, grains are first sampled at random from various locations within the field, and the observations are then reweighted according to the auxiliary variable. Data collected from three maize fields were used to compare the four sampling methods, and the results were used to determine the extent to which transgene presence rate estimation was improved by the use of stratified and reweighting sampling methods. We found that transgene rate estimates were more accurate and that substantially smaller samples could be used with sampling strategies based on an auxiliary variable derived from a gene‐flow model.     

The two-party system under alternative voting procedures

Countries that elect their policy-makers by means of Plurality Voting tend to have a two-party system. This observation can be explained by the strategic behavior of voters. This article derives two broad classes of voting procedures under which strategic voting behavior induces a two-party system under standard assumptions on voter preferences. One class consists of the voting procedures with unique top-score, i.e., under which a voter can cast a top-score vote for only one candidate (e.g., Plurality Voting, Borda Count). The other class consists of the voting procedures that permit truncated ballots, i.e., under which voters do not have to cast all their votes (e.g., Approval Voting). This analysis suggests that the key for strategic voting behavior to induce a two-party system is that voters can always cast a different score for the two candidates they rank first and second on their ballots.     

Teacher characteristics and competencies related to substance abuse prevention

Teacher characteristics and competencies perceived as beneficial for preventing substance use among students were identified through a literature search, review of existing prevention curricula, and consultation with state and local experts. These qualities were integrated into a questionnaire and administered to acknowledge professionals in the substance use and abuse arena who were affiliated with universities, public schools, and prevention/intervention agencies. A factor analysis yielded six constructs which were then scaled, examined for psychometric appropriateness, and subsequently employed to quantify perceptions of importance. Teacher-Student Relations emerged as the most important aspect of teacher comportment, followed by knowledge associated with Human Behavior, Substances, User Recognition and Referral, Prevention Curricula, and Legal Issues. These findings are encouraging in that the characteristics and skills perceived as important to prevention can be developed in both pre- and in-service teacher training.     

A new mixed first-order integer-valued autoregressive process with Poisson innovations

AStA Advances in Statistical Analysis - Integer-valued time series, seen as a collection of observations measured sequentially over time, have been studied with deep notoriety in recent years, with...     

The long-run labour market consequences of teenage motherhood in Britain

Common wisdom states that teenage childbearing reduces schooling, labour market experience and adult wages. However, the decisions to be a teenage mother, to quit school, and be less attached to the labour market might all stem from some personal or family characteristics.  Using the National Child Development Study (NCDS), we find that in Britain teenage childbearing decreases the probability of post-16 schooling by 12–24%. Employment experience is reduced by up to three years, and the adult pay differential ranges from 5% to 22%. The negative impact of teen motherhood on various adult outcomes is not only due to some pre-motherhood characteristics; hence policies aiming to encourage return to school and participation in the labour market may be an efficient way to reduce the long-term consequences of teenage pregnancy. Received: 10 October 2000/Accepted: 3 April 2002 All correspondence to Arnaud Chevalier. We are indebted to Martyn Andrews, Colm Harmon, Gauthier Lanot, Ian Walker and to the participants at the EEEG annual meeting (Southampton, 2000) and seminars at Keele University, LSE and Warwick University for their comments that greatly improved earlier versions of this paper. We also thank two anonymous referees and Christoph Schmidt for their insightful comments. All remaining errors are ours. The data was supplied by the Economic and Research Council's Data Archive at the University of Essex and are used with permission of the Controller of Her Majesty's Stationery Office. Responsible editor: Christoph M. Schmidt.     

French astronomy during the Belle Époque. The professionalization of a scientific activity

The article describes the way French astronomy developed during the Belle Époque (ca. 1880–1914). It identifies and accounts for the particulars of a scientific occupation, which until today has been misrepresented in the history of science. We show how the practice of astronomy was rigidly rationalized and integrated into a scientific-bureaucratic regime. Established in state observatories (e.g. the Paris Observatory), astronomy was defined as a professional activity practiced by a group of “workers” of the sky. Analysis enables us to shed some light on how the cognitive content of astronomy as a discipline, the institutional framework constituted by the state observatories, and the group of professional astronomers all interacted and were in fact co-constructed.     

Theory‐of‐mind during childhood: Investigating syntactic and executive contributions

Both syntax and Executive Functions (EF) are involved in Theory‐of‐Mind (ToM) but their contributory roles have mainly been studied separately. Moreover, researchers have mostly administered False Belief (FB) tasks while they may not be representative of all ToM abilities. Studies of adults give valuable information regarding whether syntax and EF are useful for ToM reasoning (i.e., Reasoning account), however, only the study of children brings direct evidence in favor of ToM emergence (i.e., Emergence account). Also, because the ToM tasks used often entail verbal and executive demands, the links observed could mostly result from such confounds (i.e., Expression account). We evaluated ToM, syntactic and EF abilities in 126 children (3‐11 y.o.) using a set of ToM tasks with minimal verbal and executive demands. Our goals were to assess (1) the hierarchical contribution of syntax and EF to ToM, (2) whether results previously obtained for FB tasks are representative of ToM in general, (3) whether the ToM‐syntax and ToM‐EF links are constant (i.e., Reasoning account) or decrease during development (i.e., Emergence accounts). Results of stepwise regression analyses showed a predominant role of syntax over EF to predict ToM abilities. The comparison of results for ToM and FB tasks showed that FB is not always representative of ToM. Finally, there was no moderating effect of age on the syntax‐ToM or EF‐ToM relations, thus suggestive of the Reasoning account rather than the Emergence account.     

An efficient computational approach for prior sensitivity analysis and cross‐validation

Prior sensitivity analysis and cross‐validation are important tools in Bayesian statistics. However, due to the computational expense of implementing existing methods, these techniques are rarely used. In this paper, the authors show how it is possible to use sequential Monte Carlo methods to create an efficient and automated algorithm to perform these tasks. They apply the algorithm to the computation of regularization path plots and to assess the sensitivity of the tuning parameter in g‐prior model selection. They then demonstrate the algorithm in a cross‐validation context and use it to select the shrinkage parameter in Bayesian regression. The Canadian Journal of Statistics 38:47–64; 2010 © 2010 Statistical Society of Canada