Archive for airport

ABC for COVID spread reconstruction

Posted in Books, pictures, Statistics, Travel with tags , , , , , , , , , on December 27, 2021 by xi'an

A recent Nature paper by Jessica Davis et al. (with an assessment by Simon Cauchemez and X from INSERM) reassessed the appearance of COVID in European and American States. Accounting for the massive under-reporting in the early days since there was no testing. The approach is based on a complex dynamic model whose parameters are estimated by an ABC algorithm (the reference being the PLoS article that initiated the ABC Wikipedia page). Results are quite interesting in that the distribution of the entry dates covers a calendar as early as December 2019 in most cases. And a proportion of missed cases as high as 99%.

“As evidence, E, we considered the cumulative number of SARS-CoV-2 cases internationally imported from China up to January 21, 2020″

The model behind remain a classical SLIR model but with a discrete and stochastic dynamical and a geographical compartmentalization based on a Voronoi tessellation centred at airports, commuting intensity and population density. Interventions by local and State authorities are also accounted for. The ABC version is a standard rejection algorithm with distance based on the evidence as quoted above. Which is a form of cdf distance (as in our Wasserstein ABC paper). For the posterior distribution of the IFR,  a second ABC algorithm uses the relative distance between observed and generated deaths (per country). The paper further investigates different introduction sources (countries) before local transmission was established. For instance, China is shown to be the dominant source for the first EU countries impacted by the pandemics such as Italy, UK, Germany, France and Spain. Using a “counterfactual scenario where the surveillance systems of the US states and European countries are imagined to operate at levels able to identify 50% of all imported and locally generated infections”, the authors conclude that

“broadening testing specifications could have considerably slowed the pandemic progression, buying considerable time to prepare mitigation responses.”

three decades back

Posted in Kids, Travel with tags , , , , , , , , , on October 25, 2021 by xi'an

Yesterday, I (we) found myself (ourselves) back in time, precisely 34 years ago, as we drove our daughter to Orly airport for her flight to Cayenne, French Guiana. And the start of her internship. Indeed, this is also the airport from which I left for Purdue University in 1987 and where my parents drove me then, more for sentimental reasons than out of necessity, as I had much less luggage than Rachel! This old airport has not changed that much, apart from the sharp increase in security restrictions. At the time, my parents were able to stay till the plane to Chicago left (two hours late) and watch it take off from the terraces of the airport. This time, we were just unable to enter the airport beyond the parking lot and watched the plane take off (one hour late) from a flight tracker! But overall there was the same bittersweet feeling of seeing one’s kid move (far) away for a major and exciting step in their professional life. (When I called my mom to watch for the plane flying west straight across Normandy, very close to our family roots, she reminded me of that and also of my grand-parents watching my plane flying by… Without a flight tracker! I actually remember spotting Mont Saint-Michel on that trip.) Fare well, Dr. R, and see you soon!


Posted in pictures, Travel with tags , , , , , , , , , , , on January 12, 2020 by xi'an

airport static

Posted in Statistics with tags , , , , on February 8, 2019 by xi'an

[An annoyingly loud businessman negotiating a deal for hours in Birmingham airport]

…you are left with this money and you get the 60, we get 107 is the mathematics…if we discount 40% Werner still gets that, it’s not well-presented, you should get that minus that, do you mind if we do it from scratch, call me back in 20mn!

snapshot from Hannover [#3]

Posted in pictures, Running, Travel with tags , , , , , , on July 11, 2015 by xi'an

LandesvaterEnd of my workshop in Hannover. Almost ended up with a mini-disaster as I misunderstood the instructions [in German] on my platform this morning (at 5:30am) and took the (wrong) train in the opposite direction from the airport. Happily enough, I realised it quickly, managed to get a bus from the following suburban station, then spotted a waiting taxi along the road who took me to the airport in half the official time (albeit driving at legal speeds) and I was through security in a few minutes in an empty airport. Just failed to buy (good) German bread at both the Bahnhof (too early) and at the Flughafen (too late). Quite an exciting couple of days!

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