
A Math Model Is Predicting the Ebola Outbreak - mikeleeorg
http://motherboard.vice.com/read/this-math-model-is-predicting-the-ebola-outbreak-with-incredible-accuracy
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throwaway_yy2Di
I think these models are extremely suspect, with nil predictive value. Where
you have sustained exponential growth dynamics, as here, the results are
_fantastically_ sensitive to the parameters which go in the exponent, which in
this case you can't predict with enough accuracy.

The simplest ODE is something like:

du/dt = k(t) * u(t)

Whose solution _locally_ looks like (for slow-varying k(t))

u(t) ∝ e^{ k(t) * t }

One possibility is k(t) > 0 sustained for 10 effective doubling times. One
possibility is k(t) < 0\. In this epidemic, either is plausible (?): the
difference is only a small difference in some infection control parameters. A
small uncertainty that translates into a _factor of a thousand uncertainty_ in
the outcome, because it gets blown up by a gigantic e^x.

And the estimates of k(t) seem to hover around the critical value of k(t) ~ 0.
In the CDC model (their Excel spreadsheet is open source [0], and FYI won't
import into LibreOffice), the shape of the epidemic is purely determined by
the shape of their k(t) assumptions. Their defaults parameter exhibit, first,
a fast growth phase, assuming k(t) > 0; then they assume a slight reduction to
k(t) ~ 0, leading to slower growth; then slightly more reduction to k(t) < 0,
causing the epidemic to halt. As far as I can tell k(t) is basically
speculative, and completely determines the shape of u(t). So really you
predict nothing.

[0]
[http://stacks.cdc.gov/view/cdc/24900](http://stacks.cdc.gov/view/cdc/24900)

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quarterwave
Well put.

A 'predictive model' should say 'if you do X then you will end up with Y' \-
and the X cannot be adjusting some number. The X has to be stuff like
'building ETU's in West Africa', or 'canceling all flights',... A predictive
model should be able to say 'don't bother canceling flights, it's no use -
instead do this...'.

Note: I'm going to be teaching a course in Erlang programming next month where
the homework assignment is epidemic modeling - 100K's of concurrent processes
moving around, getting exposed to each other - that sort of stuff. Rather
ambitious, but I feel it's a good use case for Erlang - a pandemic is a
'viral' chat application.

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tjmaglio
Is the course your teaching going be a MOOC or will the assignments be posted
publicly? I'd love to try that assignment myself.

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quarterwave
Course is classroom format. i will post the assignment on github.

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themgt
This is really, really weak sauce. They show right on the graph it following
the trend line for reported cases, which looks to already be leveling off.

The problem is, as the WHO has made very, very clear: "Problems with data
gathering in Liberia continue. It should be emphasized that the reported fall
in the number of new cases in Liberia over the past three weeks is unlikely to
be genuine. Rather, it reflects a deterioration in the ability of overwhelmed
responders to record accurate epidemiological data. It is clear from field
reports and first responders that EVD cases are being under-reported from
several key locations, and laboratory data that have not yet been integrated
into official estimates indicate an increase in the number of new cases in
Liberia. There is no evidence that the EVD epidemic in West Africa is being
brought under control ...

Evidence obtained from responders and laboratory staff in [Liberia] indicates
beyond doubt that there is widespread under-reporting of new cases, and that
the situation in Liberia, and in Monrovia in particular, continues to
deteriorate from week to week. Approximately 200 new probable and suspected
cases, but very few confirmed cases, have been reported in the capital
Monrovia in each of the past three weeks. A substantial proportion of these
suspected cases are most probably genuine cases of EVD, and the reported fall
in confirmed cases over the past three weeks reflects delays in matching
laboratory results with clinical surveillance data. Efforts continue to
urgently address problems with data acquisition in what is an extremely
challenging environment, and it is likely that the figures will be revised
upwards in due course."

In other words, awesome job building a model that fits garbage data.

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quotient
_Incredible Accuracy_? You mean _retrospectively fitting a logistic model to
something known to grow logistically_? I'm not impressed, especially not by
retrospective modelling.

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api_or_ipa
Here's the link for the referenced paper. I find it mostly accessible to the
average science graduate.

[http://www.plosone.org/article/fetchObject.action?uri=info%3...](http://www.plosone.org/article/fetchObject.action?uri=info%3Adoi%2F10.1371%2Fjournal.pone.0083622&representation=PDF)

Perhaps someone can help discuss the merits of this particular model? In my
humble opinion, I suspect a lack of empirically gathered results and support
for it's justifications. On the other hand, what qualifies as a
representational event if we're supposed to prevent human death?

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DanielBMarkham
I'm voting this up. People should be aware that it's out there. But this story
is worse than bad. It's the epidemiological equivalent of startups with nice
spreadsheets and graphs -- there are so many hidden assumptions and unknowns,
I'm not sure it's possible to make it into anything useful.

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trhway
one of the important factor seems to be missing is the negative feedback loop
- the more devastating the outbreak the more resources will be thrown at it

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jdiez17
That's a positive feedback loop. A negative feedback loop would cause people
to throw more resources at the outbreak until the derivative of the number of
cases approaches zero.

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illumen
Wow, a mainstream news source covering mathematics. This is news.

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tempodox
No offence, but a mathematical model can be made to “prove” anything,
including the half-inch pink elephant that lives in my desk drawer.

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72deluxe
Hari Seldon, is that you?

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72deluxe
Not sure on the downvotes but obviously someone didn't appreciate my reference
to Asimov's Foundation trilogy and the mathematical predictions of social
behaviour.

It all falls over when The Mule appears! (Sorry if this is a spoiler for you)

