A methodological note on the making of causal statements in the debate on anthropogenic global warming

At best, the empirical evidence for human impact on climate change, more specifically, the anthropogenic global warming (AGW), is based on correlational research. That is, no experiment has been carried out that confirms or falsifies the causal hypothesis put forward by the International Panel on Climate Change (IPCC) that anthropogenic increasing of green house gas concentrations very likely causes increasing of the (mean) global temperature. In this article, we point out the major weaknesses of correlational research in assessing causal hypotheses. We further point out that the AGW hypothesis is in need of potential falsifiers in the Popperian (neopositivistic) sense. Some directions for future research on the formulation of such falsifiers in causal research are discussed. Of course, failure to find falsifying evidence in empirical climate data will render the AWG hypothesis much stronger

Fluctuation-dissipation relationship in chaotic dynamics

We consider a general N-degree-of-freedom dissipative system which admits of chaotic behaviour. Based on a Fokker-Planck description associated with the dynamics we establish that the drift and the diffusion coefficients can be related through a set of stochastic parameters which characterize the steady state of the dynamical system in a way similar to fluctuation-dissipation relation in non-equilibrium statistical mechanics. The proposed relationship is verified by numerical experiments on a driven double well system.Comment: Revtex, 23 pages, 2 figure

Piecewise Approximate Bayesian Computation: fast inference for discretely observed Markov models using a factorised posterior distribution

Many modern statistical applications involve inference for complicated stochastic models for which the likelihood function is difficult or even impossible to calculate, and hence conventional likelihood-based inferential techniques cannot be used. In such settings, Bayesian inference can be performed using Approximate Bayesian Computation (ABC). However, in spite of many recent developments to ABC methodology, in many applications the computational cost of ABC necessitates the choice of summary statistics and tolerances that can potentially severely bias the estimate of the posterior. We propose a new “piecewise” ABC approach suitable for discretely observed Markov models that involves writing the posterior density of the parameters as a product of factors, each a function of only a subset of the data, and then using ABC within each factor. The approach has the advantage of side-stepping the need to choose a summary statistic and it enables a stringent tolerance to be set, making the posterior “less approximate”. We investigate two methods for estimating the posterior density based on ABC samples for each of the factors: the first is to use a Gaussian approximation for each factor, and the second is to use a kernel density estimate. Both methods have their merits. The Gaussian approximation is simple, fast, and probably adequate for many applications. On the other hand, using instead a kernel density estimate has the benefit of consistently estimating the true piecewise ABC posterior as the number of ABC samples tends to infinity. We illustrate the piecewise ABC approach with four examples; in each case, the approach offers fast and accurate inference

A longitudinal and cross-sectional study of Epstein-Barr virus DNA load: a possible predictor of AIDS-related lymphoma in HIV-infected patients

Introduction: HIV-infected patients are more than 100-fold greater at risk for developing malignant AIDS-related lymphoma (ARL) compared to the general population. Most ARLs are EBV related. The main purpose of this study was to investigate whether a high peak EBV DNA load in HIV-infected patients is predictive of ARL, including classical Hodgkin lymphoma. Methods: From an ongoing prospective HIV positive cohort study, we conducted a case-control study between 2004 and 2016 among patients from whom at least one EBV DNA load in serum or plasma was available. We compared peak EBV DNA load between patients with (49 cases) and without ARL (156 controls). Results: The geometric mean of the peak EBV DNA load measured before diagnosis of malignant lymphoma was 52,565 IU/mL in EBER-positive lymphoma patients vs. 127 IU/mL in controls (p 100,000 IU/mL have an increased risk for diagnosis of malignant lymphoma compared to patients with EBV DNA loads ≤100,000 IU/mL (adjusted OR 12.53; 95%CI: 4.08; 38.42). In the longitudinal study, including 13 patients with at least three left-over plasma samples available for retesting, measurements of EBV-DNA during the preceding 12 months proved to be of poor value for predicting subsequent lymphoma diagnosis. Conclusions: A EBV DNA load >100,000 IU/mL can be useful in clinical setting to accelerate time to diagnosis and treatment. EBV-DNA loads in samples taken during the preceding year of ARL diagnosis showed to be of poor predictive value

Factors Associated with Revision Surgery after Internal Fixation of Hip Fractures

Background: Femoral neck fractures are associated with high rates of revision surgery after management with internal fixation. Using data from the Fixation using Alternative Implants for the Treatment of Hip fractures (FAITH) trial evaluating methods of internal fixation in patients with femoral neck fractures, we investigated associations between baseline and surgical factors and the need for revision surgery to promote healing, relieve pain, treat infection or improve function over 24 months postsurgery. Additionally, we investigated factors associated with (1) hardware removal and (2) implant exchange from cancellous screws (CS) or sliding hip screw (SHS) to total hip arthroplasty, hemiarthroplasty, or another internal fixation device. Methods: We identified 15 potential factors a priori that may be associated with revision surgery, 7 with hardware removal, and 14 with implant exchange. We used multivariable Cox proportional hazards analyses in our investigation. Results: Factors associated with increased risk of revision surgery included: female sex, [hazard ratio (HR) 1.79, 95% confidence interval (CI) 1.25-2.50; P = 0.001], higher body mass index (fo

Verwaarloosde organisaties: (Her-)opvoeden een vergeten taak van de manager

Kampen en Schuiling vroegen zich af waarom de gebruikelijke veranderstrategieën en –interventies niet werken in organisaties die al vele reorganisaties achter de rug hebben en symptomen van verwaarlozing vertoonden. Zij vonden geen afdoende verklaring voor het mislukken van de veranderstrategieën in de managementliteratuur, zelfs niet in theorieën uit de Tavistock-traditie. Het viel hen op dat er in de theorie over organisatieverandering nauwelijks aandacht wordt besteed aan de veranderhistorie die een bedrijf of instelling heeft doorgemaakt en dat er bij elke verandering impliciet vanuit gegaan wordt dat de organisatie gezond is. In de door hen bestudeerde cases was sprake van een structureel gebrek aan belangstelling van de managers in de competenties, het gedrag, de frustraties en de ambities van hun medewerkers. Veelal onder druk van buiten namen de managers hun toevlucht tot machts-dwang strategieën om verandering te bewerkstellingen in de problematische organisaties. Dit werkte niet of had zelfs averechts effect. Echter, de toepassing van participatieve veranderstrategieën werkte evenmin. De medewerkers hadden alle vertrouwen in het management verloren. In hun onderzoek naar de verschijnselen in lastig te veranderen organisaties, zoals het Gemeentevervoerbedrijf Amsterdam en de Sociale Dienst van Amsterdam, kwamen zij de sleutelbegrippen tegen in de pedagogische literatuur. Zij ontdekten een frappante overeenkomst in de beschrijving van het gedrag van emotioneel verwaarloosde kinderen. Kinderen die door hun ouders of verzorgers zijn verwaarloosd lijden aan een reactieve hechtingsstoornis. Zij zijn niet langer in staat om op normale wijze te reageren op hun ouders of verzorgers. De relatie is verbroken. Dit lijkt heel erg op het gedrag van medewerkers in verwaarloosde organisaties. De pedagogische literatuur biedt ons het inzicht dat de managers eerst de verbinding weer moeten herstellen met hun personeel én dat zij een reële prestatieverwachting met hen dienen af te spreken die past bij hun mentale conditie. Mensen herwinnen hun zelfvertrouwen wanneer zij positieve feedback krijgen op het volbrengen van die prestatie. Vervolgens kunnen de manager én de medewerker geleidelijk de taken verzwaren. Kampen en Schuiling stellen dat de meest effectieve veranderstrategie in verwaarloosde organisaties normatief relationeel is. Zij beschouwen dit als een noodzakelijke uitbreiding op de drie veranderstrategieën machts-dwang, empirisch-rationeel en normatief-reëducatief zoals door Chin & Benne zijn onderscheiden. Omdat de relatie centraal staat in verwaarloosde organisaties stelt dit eisen aan de competenties van de change agents: het vermogen om relaties te vormen en te behouden. Hierbij gaat het zoals de pedagogiek leert om de ‘juiste opvoedingshouding’: accepteren (responsief zijn) en eisen stellen (of verwachtingen uiten). Op die wijze kunnen relationele vermogens van medewerkers en managers hersteld worden. Dit zijn langdurige processen, die ook een bijzondere relatie tussen adviseur en opdrachtgever vereisen