Regression modelling of interval censored data based on the adaptive ridge procedure

A new method for the analysis of time to ankylosis complication on a dataset of replanted teeth is proposed. In this context of left-censored, interval-censored and right-censored data, a Cox model with piecewise constant baseline hazard is introduced. Estimation is carried out with the expectation maximisation (EM) algorithm by treating the true event times as unobserved variables. This estimation procedure is shown to produce a block diagonal Hessian matrix of the baseline parameters. Taking advantage of this interesting feature in the EM algorithm, a L0 penalised likelihood method is implemented in order to automatically determine the number and locations of the cuts of the baseline hazard. This procedure allows to detect specific areas of time where patients are at greater risks for ankylosis. The method can be directly extended to the inclusion of exact observations and to a cure fraction. Theoretical results are obtained which allow to derive statistical inference of the model parameters from asymptotic likelihood theory. Through simulation studies, the penalisation technique is shown to provide a good fit of the baseline hazard and precise estimations of the resulting regression parameters.     

A robust coefficient of determination for regression

To assess the quality of the fit in a multiple linear regression, the coefficient of determination or R² is a very simple tool, yet the most used by practitioners. Indeed, it is reported in most statistical analyzes, and although it is not recommended as a final model selection tool, it provides an indication of the suitability of the chosen explanatory variables in predicting the response. In the classical setting, it is well known that the least-squares fit and coefficient of determination can be arbitrary and/or misleading in the presence of a single outlier. In many applied settings, the assumption of normality of the errors and the absence of outliers are difficult to establish. In these cases, robust procedures for estimation and inference in linear regression are available and provide a suitable alternative.     

Le télétravail des cadres : entre suractivité et apprentissage de nouvelles temporalités

Telework is often considered to be a means for making life at work and at home more compatible. Why do some wage-earners, in particular white-collar employees, choose it? Do they actually make a choice or simply adopt a solution “for want of anything better” in an organizational context with its limitations? In this case, what factors do they weigh against each other? Once they have opted for telework, how do these white collars manage to adjust their occupational and family lives? Is their aspiration to improve the balance between the two satisfied? Or do they run up against unexpected difficulties? Answers to these questions come out of two studies conducted among white-collar employees in different sorts of telework. Given the absence of institutional regulations governing the relation between life at home and at work, telework, far from leading to a more balanced life, jeopardizes the organization’s collective efficiency.     

Uncertainty and Sensitivity Analysis in Assessment of the Thyroid Cancer Risk Related to Chernobyl Fallout in Eastern France

The increase in the thyroid cancer incidence in France observed over the last 20 years has raised public concern about its association with the 1986 nuclear power plant accident at Chernobyl. At the request of French authorities, a first study sought to quantify the possible risk of thyroid cancer associated with the Chernobyl fallout in France. This study suffered from two limitations. The first involved the lack of knowledge of spontaneous thyroid cancer incidence rates (in the absence of exposure), which was especially necessary to take their trends into account for projections over time; the second was the failure to consider the uncertainties. The aim of this article is to enhance the initial thyroid cancer risk assessment for the period 1991-2007 in the area of France most exposed to the fallout (i.e., eastern France) and thereby mitigate these limitations. We consider the changes over time in the incidence of spontaneous thyroid cancer and conduct both uncertainty and sensitivity analyses. The number of spontaneous thyroid cancers was estimated from French cancer registries on the basis of two scenarios: one with a constant incidence, the other using the trend observed. Thyroid doses were estimated from all available data about contamination in France from Chernobyl fallout. Results from a 1995 pooled analysis published by Ron et al. were used to determine the dose-response relation. Depending on the scenario, the number of spontaneous thyroid cancer cases ranges from 894 (90% CI: 869-920) to 1,716 (90% CI: 1,691-1,741). The number of excess thyroid cancer cases predicted ranges from 5 (90% UI: 1-15) to 63 (90% UI: 12-180). All of the assumptions underlying the thyroid cancer risk assessment are discussed.     

Reconciling Work, Family and Child Outcomes: What Implications for Family Support Policies?

This paper discusses the potential of family policies to reconcile the multiple objectives that they are expected to serve, over and above their role in offsetting the economic cost of children. We start by emphasizing the need to consider the multiple challenges that family policies in European Union??and/or OECD??countries have to address through a broadening of the standard economic approach to the cost of children. Policies indeed aim to reduce the ??direct?? monetary cost of raising children, but they also aim to minimise the indirect cost arising from the incidence of children on the parents?? work-life balance and on the aggregate level of employment. Moreover, motives for policy intervention such as concerns about child development, gender equity or aggregate fertility levels are not fully captured by cost measurements. We thus analyse how, and to what extent, family policies can successfully reconcile these multidimensional objectives. We offer a holistic approach, pointing out that a coherent family policy mix supporting working parents with preschool children is the only way to reconcile or limit the conflicts between work, family and child outcomes. Three main dichotomies are identified to explain cross-country differences in family policy packages: the emphasis on poverty alleviation; the supposed antagonism between fertility and female employment; and the potential conflict between this latter and child development. Ways to reconcile these objectives and to improve the effectiveness and efficiency of family policies are further discussed.     

Separating curvature and elevation: A parametric probability weighting function

This paper presents a preference foundation for a two-parameter family of probability weighting functions. We provide a theoretical link between the well-established notions of probabilistic risk attitudes (i.e., optimism and pessimism) used in economics and the important independent measures for individual behavior used in the psychology literature (i.e., curvature and elevation). One of the parameters in our model measures curvature and represents the diminishing effect of optimism and pessimism when moving away from extreme probabilities 0 and 1. The other parameter measures elevation and represents the relative strength of optimism vs. pessimism. Our empirical analysis indicates that the new weighting function fits elicited probability weights well, and that it can explain differences in the treatment of probabilities for gains compared to that for probabilities of losses.