Nonparametric causal effects based on marginal structural models

A parametric marginal structural model (PMSM) approach to Causal Inference has been favored since the introduction of MSMs by Robins [1998a. Marginal structural models. In: 1997 Proceedings of the American Statistical Association. American Statistical Association, Alexandria, VA, pp. 1–10]. We propose an alternative, nonparametric MSM (NPMSM) approach that extends the definition of causal parameters of interest and causal effects. This approach is appealing in practice as it does not require correct specification of a parametric model but instead relies on a working model which can be willingly misspecified. We propose a methodology for longitudinal data to generate and estimate so-called NPMSM parameters describing so-called nonparametric causal effects and provide insight on how to interpret these parameters causally in practice. Results are illustrated with a point treatment simulation study. The proposed NPMSM approach to Causal Inference is compared to the more typical PMSM approach and we contribute to the general understanding of PMSM estimation by addressing the issue of PMSM misspecification.     

Bivariate Longitudinal Model for Detecting Prescribing Change in Two Drugs Simultaneously with Correlated Errors

Bivariate responses of repeated measures data are usually analysed as two separate responses in the literature by several authors. The two responses usually tend to be related in some way and analysing this data jointly presents an opportunity to account for the joint movement, which may impact on the conclusions reached compared to analysing the responses separately. In this paper, a bivariate regression model with random effects (linear mixed model) is used to detect a change if any in the prescribing habits in the UK at the general practice (family medicine) level due to an educational intervention given repeated measures data before and after the intervention and a control group. The message was to increase the prescribing of one drug while simultaneously decreasing the prescribing of another. The effects of modelling a bivariate auto-regressive process are evaluated.     

Analysis of longitudinal data with drop-out: objectives, assumptions and a proposal

Summary. The problem of analysing longitudinal data that are complicated by possibly informative drop-out has received considerable attention in the statistical literature. Most researchers have concentrated on either methodology or application, but we begin this paper by arguing that more attention could be given to study objectives and to the relevant targets for inference. Next we summarize a variety of approaches that have been suggested for dealing with drop-out. A long-standing concern in this subject area is that all methods require untestable assumptions. We discuss circumstances in which we are willing to make such assumptions and we propose a new and computationally efficient modelling and analysis procedure for these situations. We assume a dynamic linear model for the expected increments of a constructed variable, under which subject-specific random effects follow a martingale process in the absence of drop-out. Informal diagnostic procedures to assess the tenability of the assumption are proposed. The paper is completed by simulations and a comparison of our method and several alternatives in the analysis of data from a trial into the treatment of schizophrenia, in which approximately 50% of recruited subjects dropped out before the final scheduled measurement time.     

Das Eignungsfeststellungsverfahren für angehende Hauptfachstudierende der Soziologie

This article presents preliminary experience with a selection procedure for the diploma study course in sociology at the LMU Munich, which was first implemented in the winter term 2004/05. Furthermore, it examines the consequences of this procedure. The selection procedure, which is limited in time, was established due to high discontinuation rates and a remarkable congestion of the scientific personnel who are particularly involved in the foundation courses. Judicial fundament of the procedure is an “experimental clause” in the Bavarian University Act. First of all we point out that the number of newly registered undergraduates remarkably declined. Even the total number of applicants is lower than in the years before the initiation of the selection procedure. Secondly, we consider the dwindling during the process of the selection procedure. Contrary to some apprehensions it is obvious that applicants with a good university-entrance diploma do not choose possible alternatives, but still consider the diploma study course in sociology. Concerning the overall evaluation of the selection procedure’s consequences our results show thirdly, that the procedure is highly accepted by all parties concerned and that it therefore has to be regarded as an efficient solution to lower the discontinuation rates as well as to cope with the capacity overload.     

Helge Pross-Preis 2007 der Universität Siegen an Cornelia Helfferich

Ohne Zusammenfassung     

Are football referees really biased and inconsistent?: evidence on the incidence of disciplinary sanction in the English Premier League

Summary.  The paper presents a statistical analysis of patterns in the incidence of disciplinary sanction (yellow and red cards) that were taken against players in the English Premier League over the period 1996–2003. Several questions concerning sources of inconsistency and bias in refereeing standards are examined. Evidence is found to support a time consistency hypothesis, that the average incidence of disciplinary sanction is predominantly stable over time. However, a refereeing consistency hypothesis, that the incidence of disciplinary sanction does not vary between referees, is rejected. The tendency for away teams to incur more disciplinary points than home teams cannot be attributed to the home advantage effect on match results and appears to be due to a refereeing bias favouring the home team.     

Peer assistance for personal assistance: analysis of online discussions about personal assistance from a Swedish web forum for disabled people

This paper describes and analyses a community of disabled people in Sweden that use an online forum to discuss personal assistance issues. The forum is a community of practice (CoP) that has its roots in everyday living with personal assistance. The contributions to the forum were studied over a 4½ year period, including a total of 2755 postings from 146 persons. The levels of the CoP learning system were analysed using the FACE tool, which examines function based on attitude, control and enabling. The results indicate that a learning system was established within the CoP that made it possible for disabled people to complement, confront and counterbalance the influences of existing learning systems, theories and methods of professionals in the area of personal assistance.     

The Parent's Capacity to Treat the Child as a Psychological Agent: Constructs, Measures and Implications for Developmental Psychopathology

Recent studies of the relationship between parenting and child development have included a focus on the parent's capacity to treat the child as a psychological agent. Several constructs have been developed to refer to this capacity, for example maternal mind-mindedness, reflective functioning, and parental mentalizing. In this review article, we compare and contrast different constructs from diverse theoretical backgrounds that have been developed to operationalize parental mentalizing. We examine the empirical evidence to date in support of each of the constructs and review the relevant measures associated with each construct. Next, we discuss the possibility that these apparently diverse constructs may tap into the same underlying neurobiological socio-cognitive system. We conclude by proposing a testable model for describing the links between parental mentalization, the development of mentalizing in children, and child psychopathology.     

The coexistence of Fox (Sciurus niger) and gray (S. caroliniensis) squirrels in the Chicago metropolitan area

Two species of tree squirrel inhabit the Chicago region, the fox (Sciurus niger) and gray (S. caroliniensis) squirrel. Chicago residents submitted squirrel observations and associated landscape variables via a Website, allowing us to map squirrel distributions. Data were analyzed for patterns of correlation. At a smaller scale, we did a foot survey of fox and gray squirrels in the suburb of Oak Park, replicating an earlier study and comparing results. Gray squirrels were associated with densely populated areas, parks and campuses, fox squirrels with suburban areas. Compared to gray squirrels, fox squirrels were more likely to be observed in areas of high cat density. In the suburb of Oak Park, the current trend seems to be an extension of gray squirrel distribution and a decrease in fox squirrel distribution. Our study provides support for the idea that fox and gray squirrel coexistence is facilitated by a trade-off between managing the cost of predation and foraging efficiency, gray squirrels out-competing fox squirrels in areas of high food and low predator (or pet) density.     

COUPLING COUPLES WITH COPULAS: ANALYSIS OF ASSORTATIVE MATCHING ON RISK ATTITUDE

We investigate patterns of assortative matching on risk attitude, using self‐reported (ordinal) data on risk attitudes for males and females within married couples, from the German Socio‐Economic Panel over the period 2004–2012. We apply a novel copula‐based bivariate panel ordinal model. Estimation is in two steps: first, a copula‐based Markov model is used to relate the marginal distribution of the response in different time periods, separately for males and females; second, another copula is used to couple the males' and females' conditional (on the past) distributions. We find positive dependence, both in the middle of the distribution, and in the joint tails, and we interpret this as positive assortative matching (PAM). Hence we reject standard assortative matching theories based on risk‐sharing assumptions, and favor models based on alternative assumptions such as the ability of agents to control income risk. We also find evidence of “assimilation”; that is, PAM appearing to increase with years of marriage. (JEL C33, C51, D81)