Estimating causal networks in biosphere–atmosphere interaction with the PCMCI approach

Local meteorological conditions and biospheric activity are tightly coupled. Understanding these links is an essential prerequisite for predicting the Earth system under climate change conditions. However, many empirical studies on the interaction between the biosphere and the atmosphere are based on correlative approaches that are not able to deduce causal paths, and only very few studies apply causal discovery methods. Here, we use a recently proposed causal graph discovery algorithm, which aims to reconstruct the causal dependency structure underlying a set of time series. We explore the potential of this method to infer temporal dependencies in biosphere-atmosphere interactions. Specifically we address the following questions: How do periodicity and heteroscedasticity influence causal detection rates, i.e. the detection of existing and non-existing links? How consistent are results for noise-contaminated data? Do results exhibit an increased information content that justifies the use of this causal-inference method? We explore the first question using artificial time series with well known dependencies that mimic real-world biosphere-atmosphere interactions. The two remaining questions are addressed jointly in two case studies utilizing observational data. Firstly, we analyse three replicated eddy covariance datasets from a Mediterranean ecosystem at half hourly time resolution allowing us to understand the impact of measurement uncertainties. Secondly, we analyse global NDVI time series (GIMMS 3g) along with gridded climate data to study large-scale climatic drivers of vegetation greenness. Overall, the results confirm the capacity of the causal discovery method to extract time-lagged linear dependencies under realistic settings. The violation of the method's assumptions increases the likelihood to detect false links. Nevertheless, we consistently identify interaction patterns in observational data. Our findings suggest that estimating a directed biosphere-atmosphere network at the ecosystem level can offer novel possibilities to unravel complex multi-directional interactions. Other than classical correlative approaches, our findings are constrained to a few meaningful set of relations which can be powerful insights for the evaluation of terrestrial ecosystem models

Risk factors for unsuccessful lumbar puncture in children

Background. This descriptive study provides the first information on an association between the use of sedation and a reduction in the prevalence of unsuccessful lumbar puncture (LP) in African children of all races.Objective. Our hypothesis was that children who do not receive any procedural sedation are more likely to have unsuccessful LPs.Methods. A cross-sectional observational study examined LPs performed from February to April 2013, including details of the procedure, sedation or analgesia used, and techniques. The setting was the Medical Emergency Unit at Red Cross War Memorial Children’s Hospital, Cape Town, South Africa, and the participants all children aged 0 - 13 years who had an LP in the unit during the time period.Results. Of 350 children, 62.9% were <12 months of age, the median age being 4.8 months (interquartile range 1.5 - 21.7). The prevalence of unsuccessful (traumatic or dry) LP was 32.3% (113/350). Sedation was used in 107 children (30.6%) and was associated with a reduction in the likelihood of unsuccessful LP (p=0.002; risk ratio (RR) 0.5 (95% confidence interval (CI) 0.34 - 0.78)) except in those <3 months of age, where sedation did not significantly reduce the likelihood (p=0.56; RR 1.20 (95% CI 0.66 - 2.18)).Conclusions. Unsuccessful LP was common. Sedation was not routinely used, but the results suggest that it may be associated with a reduction in the rate of unsuccessful LP. Unsuccessful LP may lead to diagnostic uncertainty, prolonged hospitalisation and unnecessary antibiotic use. Whether a procedural sedation protocol would reduce the rate of unsuccessful LP requires further study