Evolution of recurrent asthma event rate over time in frailty models

Summary. To model the time evolution of the event rate in recurrent event data a crucial role is played by the timescale that is used. Depending on the timescale selected the interpretation of the time evolution will be entirely different, both in parametric and semiparametric frailty models. The gap timescale is more appropriate when studying the recurrent event rate as a function of time since the last event, whereas the calendar timescale keeps track of actual time. We show both timescales in action on data from an asthma prevention trial in young children. The frailty model is further extended to include both timescales simultaneously as this might be most relevant in practice.     

Turning Sexual Science Into News: Sex Research and the Media

In this article we report on the findings of a two-part project investigating contemporary issues in sexuality researchers' interaction with journalists. The goal of the project was to explore best practices and suggest curricular and training initiatives for sexuality researchers and journalists that would enhance the accurate dissemination of sexuality research results in the media. We present the results of a survey of a convenience sample of 94 sexuality researchers about their experiences and concerns regarding media coverage and a summary of the main themes that emerged from an invitational conference of sexuality researchers and journalists. In addition, we present some preliminary recommendations for training and best practices. Topics assessed include reporting accuracy; sex researchers' comfort with various topics, media, and journalists; researchers' perceptions of the purpose and content of articles; concern about the impact of media coverage; and training for sexuality researchers.     

Including the Smoking Epidemic in Internationally Coherent Mortality Projections

We present a new mortality projection methodology that distinguishes smoking- and non-smoking-related mortality and takes into account mortality trends of the opposite sex and in other countries. We evaluate to what extent future projections of life expectancy at birth (e ₀) for the Netherlands up to 2040 are affected by the application of these components. All-cause mortality and non-smoking-related mortality for the years 1970–2006 are projected by the Lee-Carter and Li-Lee methodologies. Smoking-related mortality is projected according to assumptions on future smoking-attributable mortality. Projecting all-cause mortality in the Netherlands, using the Lee-Carter model, leads to high gains in e ₀ (4.1 for males; 4.4 for females) and divergence between the sexes. Coherent projections, which include the mortality experience of the other 21 sex- and country-specific populations, result in much higher gains for males (6.4) and females (5.7), and convergence. The separate projection of smoking and non-smoking-related mortality produces a steady increase in e ₀ for males (4.8) and a nonlinear trend for females, with lower gains in e ₀ in the short run, resulting in temporary sex convergence. The latter effect is also found in coherent projections. Our methodology provides more robust projections, especially thanks to the distinction between smoking- and non-smoking-related mortality.     

Copula based flexible modeling of associations between clustered event times

Multivariate survival data are characterized by the presence of correlation between event times within the same cluster. First, we build multi-dimensional copulas with flexible and possibly symmetric dependence structures for such data. In particular, clustered right-censored survival data are modeled using mixtures of max-infinitely divisible bivariate copulas. Second, these copulas are fit by a likelihood approach where the vast amount of copula derivatives present in the likelihood is approximated by finite differences. Third, we formulate conditions for clustered right-censored survival data under which an information criterion for model selection is either weakly consistent or consistent. Several of the familiar selection criteria are included. A set of four-dimensional data on time-to-mastitis is used to demonstrate the developed methodology.     

Informal Mentoring at Work: A Review and Suggestions for Future Research

This paper reviews the literature on informal mentoring at work. Based on two basic premises of interpersonal relationships, it discusses four promising areas in current mentoring research that could be cultivated further by future research. The first premise that we hold is that relationships never exist in a vacuum. Traditionally, however, mentoring literature has often overlooked the context of mentoring. We propose that the developmental network approach can be further extended to gather more insight into the interplay between mentoring dyads and their context. Also, mentoring literature could pay more attention to temporal influences in mentoring studies. The second premise that is applied is that relationships are not only instrumental in nature. However, mentoring research to date has mostly applied a one‐sided and transactional view to mentoring. Relational mentoring theory could be helpful in examining relational motivations of both members. Also, mentoring literature can achieve more explanatory power by examining the underlying mechanisms of mentoring, next to social exchange principles, that cause these developmental changes. In summary, in each of these four research areas, we identify and discuss fundamental questions and developments in research that can advance mentoring theory and practice.     

Continuous covariate frailty models for censored and truncated clustered data

Using some logarithmic and integral transformation we transform a continuous covariate frailty model into a polynomial regression model with a random effect. The responses of this mixed model can be ‘estimated’ via conditional hazard function estimation. The random error in this model does not have zero mean and its variance is not constant along the covariate and, consequently, these two quantities have to be estimated. Since the asymptotic expression for the bias is complicated, the two-large-bandwidth trick is proposed to estimate the bias. The proposed transformation is very useful for clustered incomplete data subject to left truncation and right censoring (and for complex clustered data in general). Indeed, in this case no standard software is available to fit the frailty model, whereas for the transformed model standard software for mixed models can be used for estimating the unknown parameters in the original frailty model. A small simulation study illustrates the good behavior of the proposed method. This method is applied to a bladder cancer data set.     

Validation of prognostic indices using the frailty model

A major issue when proposing a new prognostic index is its generalisibility to daily clinical practice. Validation is therefore required. Most validation techniques assess whether “on average” the results obtained by the prognostic index in classifying patients in a new sample of patients are similar to the results obtained in the construction set. We introduce a new important aspect of the generalisibility of a prognostic index: the heterogeneity of the prognostic index risk group hazard ratios over different centers. If substantial variability between centers exists, the prognostic index may have no discriminatory capability in some of the centers. To model such heterogeneity, we use a frailty model including a random center effect and a random prognostic index by center interaction. Statistical inference is based on a Bayesian approach using a Laplacian approximation for the marginal posterior distribution of the variances of the random effects. We investigate different ways to summarize the information available from this marginal posterior distribution. Our approach is applied to a real bladder cancer database for which we demonstrate how to investigate and interpret heterogeneity in prognostic index effect over centers.     

On the asymptotic normality of functions of uniform spacings

A new proof is given for the asymptotic normality of sum functions of spacings, providing an alternative to the method of Le Cam (1958). The result is obtained under an optimal moment condition. The proof is based on a simple decomposition into a leading term, which is asymptotically normal, and a remainder term, which is shown to be negligible.     

Egalitarian: From Homophile to Helicophile in Post–World War II America

The presidency of gender in the Anglo-American taxonomy of sexualities historically has been haunted by the irruption of “other” parameters of medicalization, censure, and caesura, not in the least absolute and relative measures of age. Where today’s clinical psychologists feel the need to age-specify adult homosexuality in such Hirschfeldian terms as androphilia, however, the felt need is indeed still essentially clinical. That cosmopolitan expressions such as homosexual, LGB, or queer rarely require such specifications relies on a protracted and today, arguably, complete disarticulation of sex/gender and age/maturity as parameters of sexual orientation, accreditation, and mobilization. Notably disconnected discursive frames gave voice to this Anglophone crystallization of “the normal homosexual” (circa 1950–1980): criminological, psychiatric, psychophysiological, and psychodynamic typologies of “sexual deviation” (variably tending to correlate, align, or subsume same-sex and age-disparate intimacies); territorializing apologias of gay, but also of “Greek,” “pederast,” and “man-boy,” socialities; anthropological-historical exotification of “age-stratified homosexualities”; and mostly European, proto-queer critiques of all “bourgeois” sexual classification.