Validation of surrogate end points in multiple randomized clinical trials with failure time end points

Before a surrogate end point can replace a final (true) end point in the evaluation of an experimental treatment, it must be formally 'validated'. The validation will typically require large numbers of observations. It is therefore useful to consider situations in which data are available from several randomized experiments. For two normally distributed end points Buyse and co-workers suggested a new definition of validity in terms of the quality of both trial level and individual level associations between the surrogate and true end points. This paper extends this approach to the important case of two failure time end points, using bivariate survival modelling. The method is illustrated by using two actual sets of data from cancer clinical trials.     

MORM—A Petri Net Based Model for Assessing OH&S Risks in Industrial Processes: Modeling Qualitative Aspects

Because of the increase in workplace automation and the diversification of industrial processes, workplaces have become more and more complex. The classical approaches used to address workplace hazard concerns, such as checklists or sequence models, are, therefore, of limited use in such complex systems. Moreover, because of the multifaceted nature of workplaces, the use of single-oriented methods, such as AEA (man oriented), FMEA (system oriented), or HAZOP (process oriented), is not satisfactory. The use of a dynamic modeling approach in order to allow multiple-oriented analyses may constitute an alternative to overcome this limitation. The qualitative modeling aspects of the MORM (man-machine occupational risk modeling) model are discussed in this article. The model, realized on an object-oriented Petri net tool (CO-OPN), has been developed to simulate and analyze industrial processes in an OH&S perspective. The industrial process is modeled as a set of interconnected subnets (state spaces), which describe its constitutive machines. Process-related factors are introduced, in an explicit way, through machine interconnections and flow properties. While man-machine interactions are modeled as triggering events for the state spaces of the machines, the CREAM cognitive behavior model is used in order to establish the relevant triggering events. In the CO-OPN formalism, the model is expressed as a set of interconnected CO-OPN objects defined over data types expressing the measure attached to the flow of entities transiting through the machines. Constraints on the measures assigned to these entities are used to determine the state changes in each machine. Interconnecting machines implies the composition of such flow and consequently the interconnection of the measure constraints. This is reflected by the construction of constraint enrichment hierarchies, which can be used for simulation and analysis optimization in a clear mathematical framework. The use of Petri nets to perform multiple-oriented analysis opens perspectives in the field of industrial risk management. It may significantly reduce the duration of the assessment process. But, most of all, it opens perspectives in the field of risk comparisons and integrated risk management. Moreover, because of the generic nature of the model and tool used, the same concepts and patterns may be used to model a wide range of systems and application fields.     

Patterns of change in youth unemployment regimes: France and Switzerland compared

The comparison between France and Switzerland enables us to compare a country that has a strong interventionist tradition in the labour market and whose youth unemployment is endemically high with a more liberal country that is faced with a more recent increase in youth unemployment but which, nevertheless, remains relatively measured. Starting from different rules and values, the two youth unemployment systems resemble each other insofar as both exclude most unemployed youth from all available benefits. From this angle, French egalitarianism rejoins Swiss differentialism. In both cases, it is not the least of paradoxes that the system of unemployment insurance so little benefits those who are most vulnerable to the economic crisis and the present dearth of jobs.     

Partner Choice and the Transition to Parenthood for Second-Generation Women of Turkish and Moroccan Origin in Belgium

Studies on fertility among second-generation migrant women across Europe have mainly treated the second generation as a rather homogenous group, not linking and distinguishing fertility patterns by type of partner. This study investigates how and to what extent the origin and generation of the partner (endogamous or exogamous as well as diversity in endogamy) of Turkish and Moroccan second-generation women in Belgium is related to first-birth rates. We distinguish three types of partnerships: those in an endogamous union with a first-generation partner, those in an endogamous union with a second-generation partner, and those in an exogenous union where the partner is of native Belgian origin. We use linked Census-Register data for the period 2001–2006. Applying event history models, our findings reveal clear differences between the endogamous and exogamous unions with respect to the timing of first births. Second-generation women of both origin groups have the lowest parenthood rates when the partner is of native Belgian origin. However, no variation is found within endogamous unions. For endogamous unions with a first-generation partner, the parenthood rates are approximately the same (and not higher, as was expected) compared to when the partner is also of second generation.     

Nested Kriging predictions for datasets with a large number of observations

This work falls within the context of predicting the value of a real function at some input locations given a limited number of observations of this function. The Kriging interpolation technique (or Gaussian process regression) is often considered to tackle such a problem, but the method suffers from its computational burden when the number of observation points is large. We introduce in this article nested Kriging predictors which are constructed by aggregating sub-models based on subsets of observation points. This approach is proven to have better theoretical properties than other aggregation methods that can be found in the literature. Contrarily to some other methods it can be shown that the proposed aggregation method is consistent. Finally, the practical interest of the proposed method is illustrated on simulated datasets and on an industrial test case with \(10^4\) observations in a 6-dimensional space.     

A New Look at Gender Effects in Participation and Occupation Choice

In this paper we evaluate the extent to which changes over time in women’s labour market destinations are due to characteristics, on the one hand, and prices, on the other. Multinomial and nested logit methods are used to analyse US data for 1970 and 1990, and the results are compared. The latter method, which has not previously been employed in the present context, alleviates problems due to the strong assumption in simpler models of the independence of irrelevant alternatives, and provides much additional useful information.     

Attitudes to immigrants in South Africa: personality and vulnerability

While many countries across the world face increasing numbers of immigrants, the literature on attitudes to foreigners and immigrants focuses on Western countries. This article tests broad insights from Western countries in a specific non-Western context – South Africa, a country marked by sporadic violence against some immigrant groups. This provides an important validity check. Data from the 2013 South African Social Attitudes Survey and the 2013 World Value Survey are used to model attitudes to immigrants. In line with research on Western countries, individual personality is associated with differences in attitudes; people in vulnerable positions and those who lack a personal support mechanism are more likely to oppose immigrants. When implemented to reflect the specific context, research on attitudes to immigrants appears to generalise to non-Western contexts.