Archive for 19nCoV

simplified Bayesian analysis

Posted in Statistics with tags , , , , , , , , , , , , on February 10, 2021 by xi'an

A colleague from Dauphine sent me a paper by Carlo Graziani on a Bayesian analysis of vaccine efficiency, asking for my opinion. The Bayesian side is quite simple: given two Poisson observations, N~P(μ) and M~P(ν), there exists a reparameterisation of (μ,ν) into

e=1-μ/rν  and  λ=ν(1+(1-e)r)=μ+ν

vaccine efficiency and expectation of N+M, respectively, when r is the vaccine-to-placebo ratio of person-times at risk, ie the ratio of the numbers of participants in each group. Reparameterisation such that the likelihood factorises into a function of e and a function of λ. Using a product prior for this parameterisation leads to a posterior on e times a posterior on λ. This is a nice remark, which may have been made earlier (as for instance another approach to infer about e while treating λ as a nuisance parameter is to condition on N+M). The paper then proposes as an application of this remark an analysis of the results of three SARS-Cov-2 vaccines, meaning using the pairs (N,M) for each vaccine and deriving credible intervals, which sounds more like an exercise in basic Bayesian inference than a fundamental step in assessing the efficiency of the vaccines…

For a resilient and recovery year

Posted in Kids, pictures, Travel with tags , , , , , , , , , on January 1, 2021 by xi'an

counting COVID-19 deaths (or not)

Posted in Statistics with tags , , , , , , , , , , , on September 7, 2020 by xi'an

Two COVID-19 articles in the recent issue of Nature relating to data gathering issues. One on the difficulty to distinguish direct COVID deaths from indirect ones from the excess deaths, which “to many scientists, it’s the most robust way to gauge the impact of the pandemic” (which I supported). As indeed the COVID pandemic reduced people access to health care, both because health structures were overwhelmed and because people were scared of catching the virus when visiting these structures. The article [by Giuliana Viglione] supports the direct exploitation of death certificates, to improve the separation, quoting Natalie Dean from the University of Florida in Gainesville. Although this creates a strong lag in the reporting and hence in health policy decisions. (Assuming the overall death reporting is to be trusted, which is not the case for all countries.)

“This long-standing neglect has been exacerbated by the lack of national leadership during the pandemic.”

The other article is about the reasons why the COVID-19 crisis in the US is doubled by a COVID-19 data crisis. Mentioning “political meddling, privacy concerns and years of neglect of public-health surveillance systems” as some of the sources for unreliable data on the pandemic range and evolution. Hardly any contact tracking (as opposed to South Korea or Vietnam), a wealth of local, state and federal structures, data diverted and hence delayed (or worse) to a new system launched by the US Department for Health and Human Services (HHS) for an ill-used $10 million. And data often shared (or lost) by fax! “Lack of leadership,” to state the obvious….

Ca’ Foscari closed due to 19nCoV scare

Posted in pictures, Travel, University life with tags , , , , , , , on February 23, 2020 by xi'an

An email from the Rettore I just received on my Ca’ Foscari account, announcing the University is closed over all its campi due to some cases of Coronavirus in the Veneto region:

Care colleghe e cari colleghi tutti, care studentesse e cari studenti,

abbiamo avuto ieri e oggi la notizia di diversi casi di infezione da Coronavirus 19nCoV in Veneto, una situazione che prevede misure appropriate e la massima attenzione.

Invito innanzitutto l’intera comunità accademica a seguire con grande scrupolo le prescrizioni che l’unità di crisi regionale ha emanato, ed emanerà sulla base della evoluzione del contagio. Si raccomandano in particolare le seguenti misure di prevenzione (nota OMS e linea indirizzo MUR):
• Lavare spesso le mani con acqua e sapone o gel disinfettanti
• Quando si tossisce o starnutisce, coprire la bocca e il naso con il gomito o fazzoletto usa e getta, lavandosi poi le mani
• Evitare il contatto con chiunque abbia febbre e tosse.

Riguardo alle attività accademiche, al fine di ridurre le possibilità di contagio, si dispone – secondo le indicazioni del Presidente Luca Zaia e in coordinamento con le università del Veneto –  la sospensione delle lezioni e degli esami in tutte le sedi dell’università, a Venezia, Mestre, Treviso e Roncade dal 24/02 al 29/02 compresi. Biblioteche e aule studio saranno chiuse dal 23/02 al 01/03.
Il recupero delle lezioni e degli esami verrà comunicato quanto prima sul sito web di Ca’ Foscari e sui canali di comunicazione ufficiali.
Per il personale tutto,  docente e non docente, le attività si svolgeranno regolarmente, fatte salve le ordinanze locali che vincolino la mobilità delle persone.
L’Ateneo è in continuo contatto con l’unità di crisi e con i ministeri competenti, e provvederà ad aggiornare le misure oggi vigenti sulla base dell’evoluzione della situazione.
Il Rettore
Michele Bugliesi