Counterfactual analyses with graphical models based on local independence

We show that one can perform causal inference in a natural way for continuous-time scenarios using tools from stochastic analysis. This provides new alternatives to the positivity condition for inverse probability weighting. The probability distribution that would govern the frequency of observations in the counterfactual scenario can be characterized in terms of a so-called martingale problem. The counterfactual and factual probability distributions may be related through a likelihood ratio given by a stochastic differential equation. We can perform inference for counterfactual scenarios based on the original observations, re-weighted according to this likelihood ratio. This is possible if the solution of the stochastic differential equation is uniformly integrable, a property that can be determined by comparing the corresponding factual and counterfactual short-term predictions. Local independence graphs are directed, possibly cyclic, graphs that represent short-term prediction among sufficiently autonomous stochastic processes. We show through an example that these graphs can be used to identify and provide consistent estimators for counterfactual parameters in continuous time. This is analogous to how Judea Pearl uses graphical information to identify causal effects in finite state Bayesian networks.Comment: Published in at http://dx.doi.org/10.1214/12-AOS1031 the Annals of Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical Statistics (http://www.imstat.org

On null hypotheses in survival analysis

The conventional nonparametric tests in survival analysis, such as the log-rank test, assess the null hypothesis that the hazards are equal at all times. However, hazards are hard to interpret causally, and other null hypotheses are more relevant in many scenarios with survival outcomes. To allow for a wider range of null hypotheses, we present a generic approach to define test statistics. This approach utilizes the fact that a wide range of common parameters in survival analysis can be expressed as solutions of differential equations. Thereby we can test hypotheses based on survival parameters that solve differential equations driven by cumulative hazards, and it is easy to implement the tests on a computer. We present simulations, suggesting that our tests perform well for several hypotheses in a range of scenarios. Finally, we use our tests to evaluate the effect of adjuvant chemotherapies in patients with colon cancer, using data from a randomised controlled trial

‘Raised by Wolves ’U2,Trauma& The Troubles

Master´s thesis in English (EN500

Transforming cumulative hazard estimates

Time to event outcomes are often evaluated on the hazard scale, but interpreting hazards may be difficult. Recently, there has been concern in the causal inference literature that hazards actually have a built in selection-effect that prevents simple causal interpretations. This is even a problem in randomized controlled trials, where hazard ratios have become a standard measure of treatment effects. Modeling on the hazard scale is nevertheless convenient, e.g. to adjust for covariates. Using hazards for intermediate calculations may therefore be desirable. Here, we provide a generic method for transforming hazard estimates consistently to other scales at which these built in selection effects are avoided. The method is based on differential equations, and generalize a well known relation between the Nelson-Aalen and Kaplan-Meier estimators. Using the martingale central limit theorem we also find that covariances can be estimated consistently for a large class of estimators, thus allowing for rapid calculations of confidence intervals. Hence, given cumulative hazard estimates based on e.g. Aalen's additive hazard model, we can obtain many other parameters without much more effort. We present several examples and associated estimators. Coverage and convergence speed is explored using simulations, suggesting that reliable estimates can be obtained in real-life scenarios.Comment: 22 pages, 4 figures. Added Lemma 1 stating sufficient conditions for P-UT for our considerations, and Proposition 1 showing the conditions are satisfied for estimated additive hazard coefficients and their martingale residual

Disturbing bodies: History and trauma, in Bog Child and The Ferryman

Trauma theory is a growing field that continues to be researched by many and the use of literature as a medium for trauma theory is a field that continues to expand. The image of bodies is prominent in both the novel Bog Child by Siobhan Dowd and the play The Ferryman by Jez Butterworth. It is fascinating to look at how the image of bodies is used in these two literary works and how it can be connected to both history and trauma theory. The body used as a symbol is one of the most important aspects of the thesis: the body as in a corpse, but also the way in which one can use a living body in a symbolic way as they have done in the hunger strikes. Trauma theory can be connected to many aspects of both Bog Child and The Ferryman, and both the bog bodies and the hunger strikers play very important roles in the lives of the main characters. The closely connected role of historic events in the novel and in the play does so that the trauma theory has a prominent role in the analysis of both

Experiences of unexplained chest pain and physical activity: A Meta- Ethnography

Aims and objectives The aim was to examine the experiences of physical activity in the patients with unexplained chest pain. Background Previous qualitative studies have compiled data on the physical activity experiences of people with unexplained chest pain. Nevertheless, no meta-synthesis exists on this topic to advance the theoretical development of future-related studies. Design A meta-ethnographic synthesis of qualitative studies was conducted. Original qualitative studies on the physical activity experiences of people with unexplained chest pain were identified and systematically synthesised using a meta-ethnographic approach. Methods Seven databases were searched for relevant full-text articles in English, Danish, Norwegian and Swedish. There were no limitations concerning year of publication. Articles were first screened against inclusion criteria for eligibility and then assessed for quality and analysed using Noblit and Hare's seven-step meta-ethnography process. The ENTREQ checklist for systematic reviews was used. Results Nine qualitative studies were included in the analysis. The physical activity experiences of people with unexplained chest pain illuminates the metaphor: “Physical activity means balancing uncertainty” with four themes: looking for possible explanations, feeling vulnerable, feeling uncertain of consequences and being physically active may mean becoming more capable. Conclusion For people with unexplained chest pain, being physically active meant moving toward being more capable. The participants felt vulnerable and physical activity helped in balancing uncertainty. A comprehensive model illustrates the antecedents and succedent for the physical activity experiences of individuals with unexplained chest pains.publishedVersio