Delayed Sampling and Automatic Rao-Blackwellization of Probabilistic Programs

We introduce a dynamic mechanism for the solution of analytically-tractable substructure in probabilistic programs, using conjugate priors and affine transformations to reduce variance in Monte Carlo estimators. For inference with Sequential Monte Carlo, this automatically yields improvements such as locally-optimal proposals and Rao-Blackwellization. The mechanism maintains a directed graph alongside the running program that evolves dynamically as operations are triggered upon it. Nodes of the graph represent random variables, edges the analytically-tractable relationships between them. Random variables remain in the graph for as long as possible, to be sampled only when they are used by the program in a way that cannot be resolved analytically. In the meantime, they are conditioned on as many observations as possible. We demonstrate the mechanism with a few pedagogical examples, as well as a linear-nonlinear state-space model with simulated data, and an epidemiological model with real data of a dengue outbreak in Micronesia. In all cases one or more variables are automatically marginalized out to significantly reduce variance in estimates of the marginal likelihood, in the final case facilitating a random-weight or pseudo-marginal-type importance sampler for parameter estimation. We have implemented the approach in Anglican and a new probabilistic programming language called Birch.Comment: 13 pages, 4 figure

Toxoplasma gondii and the role of pork

Toxoplasma gondii is an important zoonotic pathogen. Humans can acquire T. gondii infection through foodborne or environmental exposure, and recent estimates suggest that more than 10 million human cases of toxoplasmosis occur globally every year. Infections in humans can be post-natal (i.e. acquired toxoplasmosis) or vertical (i.e. congenital toxoplasmosis). Because congenital toxoplasmosis is considered particu-larly problematic due to the severe health effects it can cause in children since birth and the possibility of fetal death, its public health impact has been more extensively studied than acquired toxoplasmosis, where infection is usually associated with mild flu-like symptoms. However, several newer studies suggest that in some cases ocular disease and severe syndromes such as psychiatric disorders may develop as a result of infection

Effects of grade, smiley, and text on Danish and Finnish consumers’ perceptions of food safety inspection reports

Publicly accessible food safety inspection reports are a standard procedure to inform consumers on restaurants' food safety levels in many countries. This study examined how different formats of food safety inspection report are associated with consumer perceptions related to food safety, as well as other perceptions about the restaurant. The study was conducted in Denmark and Finland with similar inspection grade systems but differences in the distribution of awarded grades. We conducted a population-based survey experiment with a between-subjects design on nationally representative samples of the 18-70 years old Danish (n = 978) and Finnish (n = 907) populations. Respondents received one of six food safety inspection reports with different combinations of inspection grade with a smiley and/or text. According to the results, both Danish and Finnish consumers' food safety perceptions of the same grade were more positive when the report included a smiley, and more negative when the report included a text. Finnish respondents perceived a good food safety inspection grade more positively than Danish respondents but there were no country differences when the grade was poor. In addition, food safety inspection results elicited perceptions that were not related to food safety in both countries. The results suggest that if the grade is poor, the inclusion of text is effective in eliciting perceptions of increased food safety risk. If the grade is good, a standalone smiley may be most effective in eliciting positive perceptions of a high food safety level. Moreover, these results indicate the importance of carefully evaluating how to develop public accessible inspection grades to ensure they are correctly interpreted by consumers in different countries.Peer reviewe

[Recension av] 1989 - Året som endret Europa

1989 – The Year That Transformed Europe Thomas Lundén (Centrum för Östersjö- och Östeuropaforskning (CBEES), Södertörns högskola) reviews 1989 – Året som endret Europa (1989 – The Year That Transformed Europe) written by Per Anders Madsen.Per Anders Madsen, Oslo: Gyldendal Norsk Forlag, 2019, 367 sidor. ISBN 9788205519787</p