A Parametric Estimation Procedure for Relapse Time Distributions

In a relapse clinical trial patients who have recovered from some recurrent disease (e.g.,ulcer or cancer) are examined at a number of predetermined times. A relapse can be detected either at one of these planned inspections or at a spontaneous visit initiated by the patient because of symptoms. In the first case the observations of the time to relapse, X, is interval-censored by two predetermined time-points. In the second case the upper endpoint of the interval is an observation of the time to symptoms,Y . To model the progression of the disease we use a partially observable Markov process. This approach results in a bivariate phase-type distribution for the joint distribution of (X,Y). It is a flexible model which contains several natural distributions for X, and allows the conditional distributions of the marginals to smoothly depend on each other. To estimate the distributions involved we develop an EM-algorithm. The estimation procedure is evaluated and compared with a non-parametric method in a couple of examples based on simulated data.     

Temporal stability of entries and predictors for entry into out-of-home care before the third birthday: A Danish population-based study of entries from 1981 to 2008

Objective

Placing a child in out-of-home care is one of the most radical measures a child protection system can decide to take. There is an essential interest in understanding the probability of entering care and what circumstances are related to the decision to place a child in out-of-home care. This study investigates the temporal stability of rates and predictors for entry into care.

Method

Data were obtained by linking several registration systems. The study population was defined as all children entering care before their third birthday from birth cohorts 1981–2008 (N = 11,034). Furthermore, a control population consisting of a randomly assigned quarter of the Danish child population from the same birth cohorts was used (N = 515,773). Rates of entry and Cox regression models from six periods from 1981 to 2008 were used to model co-variates associated with entry into out-of-home care.

Results

The overall likelihood for entering care is found to be decreasing over time. Furthermore, results reveal two trends: relative rates of entry are significantly decreasing for children whose mother has a psychiatric history prior to the child's birth; relative rates are significantly increasing for children whose mother or father was unemployed in the year prior to the child's birth.     

Inference Methods for Correlated Left Truncated Lifetimes: Parent and Offspring Relations in an Adoption Study

The associations in mortality of adult adoptees and their biological or adoptive parents have been studied in order to separate genetic and environmental influences. The 1003 Danish adoptees born 1924–26 have previously been analysed in a Cox regression model, using dichotomised versions of the parents’ lifetimes as covariates. This model will be referred to as the conditional Cox model, as it analyses lifetimes of adoptees conditional on parental lifetimes. Shared frailty models may be more satisfactory by using the entire observed lifetime of the parents. In a simulation study, sample size, distribution of lifetimes, truncation- and censoring patterns were chosen to illustrate aspects of the adoption dataset, and were generated from the conditional Cox model or a shared frailty model with gamma distributed frailties. First, efficiency was compared in the conditional Cox model and a shared frailty model, based on the conditional approach. For data with type 1 censoring the models showed no differences, whereas in data with random or no censoring, the models had different power in favour of the one from which data were generated. Secondly, estimation in the shared frailty model by a conditional approach or a two-stage copula approach was compared. Both approaches worked well, with no sign of dependence upon the truncation pattern, but some sign of bias depending on the censoring. For frailty parameters close to zero, we found bias when the estimation procedure used did not allow negative estimates. Based on this evaluation, we prefer to use frailty models allowing for negative frailty parameter estimates. The conclusions from earlier analyses of the adoption study were confirmed, though without greater precision than using the conditional Cox model. Analyses of associations between parental lifetimes are also presented.     

The transition from in-home services to out-of-home care: A Danish register-based study

Objective

This register-based study describes the transition from in home-based care to placements in out-of-home care. It also describes whether children who enter care directly differ from children who enter care after episodes of in home-based care.

Method

The study includes all children who entered the child protection system of a larger regional social service system in Denmark from 1993 to 2006 (N = 9961). Graphs of cumulative incidences were used to describe transitions into out-of-home care within two years after in home-based care started. Cox regression models are used to estimate the impacts of child and parental characteristics. In addition, Chi² tests are used to identify differences between children who enter care directly and children who receive in home-based care.

Results

Results indicate that the majority of children do not enter out-of-home care but that risks differ among age groups. Covariates did not predict transitions into out-of-home care for those who entered in-home care after becoming teenagers. Especially for those who entered in-home care before entering their teens, the psychiatric histories of the mothers and the children predicted the transitions into out-of-home care. Immigration background was a protective factor for those who entered in-home care as pre-scholars. Depending on the age group, low birth weight, children's fathers' and mothers' psychiatric histories, and single parentship were all characteristics more likely to be associated with children who entered care directly. Children who entered care directly differed from children who entered care within two years after an in home-based service had been initiated on covariates that described psychiatric history.     

Das internationale Führungsparkett – Herausforderungen,Haltegriffe und hilfreiche Schrittfolgen

Managers and executives are increasingly facing the challenge of being successful in an complex international context. This article explains the specific demands international co-operation poses on leading executives. It offers encouragement as well as methods which could be used as ‘helping grips’ when observing and coming to terms with situations in this special working environment, with the objective of offering the involved players a larger spectrum of possible action. The first part describes concrete action fields of international co-operation that managers should pay attention to in their daily international work. The second part of the article dedicates itself to the fields of intercultural competencies that are helpful for leading executives. The concluding part deals with some highly demanding general challenges of international co-operation, which managers sometimes describe as surprising and overwhelming, and which are therefore good and quite helpful to know in advance.     

Social integration and suicide: Denmark, 1906–2006

Research on the relationship between social integration and suicide rates has neglected a historical perspective. Analyses are often based on relatively short time periods where there may not be enough variation in integration to affect the national suicide rate, or where overall integration levels are not low enough to buttress a link between a specific index of low integration, such as divorce, and suicide. The present investigation contributes to the literature by testing a hypothesis on domestic integration and suicide over a century, the longest period studied to date, encompassing periods of low and high overall social integration, and emergent risk and protective factors. Data are available for core variables for Denmark, 1906–2006. Annual data include those on suicide, and indicators of integration (divorces, births, marriages), as well as for economic strain (unemployment) and time trends. A log linear Poisson model is estimated, which explores the central divorce–suicide relationship under controls for confounders. Controlling for confounders, a one percent increase in divorce increases male suicides by 0.52% and female suicides by 1.12%. As anticipated, marriages decrease suicide: a one percent increase in marriages reduces suicide by 0.77% for men and by 0.63% for women. The trend in divorce, in particular, offers accurate predictions of suicide throughout the century. The relationship between divorce and suicide over a century is robust. The results offer the strongest support to date in support of a social integration model based on long term historical data on suicide and divorce.