[Population Modeling] Re: PopModWkGrpIMAG-news Digest, Vol 3,
Issue 17
John Rice
john.rice at noboxes.org
Sat Jan 17 12:29:47 PST 2015
Talitha, et.al.,
As a naive observer I willingly accept the risk of asking questions or
making suggestions that may not be of interest or even relevant. That said.
1. WRT to non living "populations":
Think about guardrails on the interstate. There are thousands of metal
I-beams sunk into the ground to be the posts to which the rails are
attached. I suspect that engineers did models to determine the
characteristics of the material of which they are made, their shape, size
and and implantation. In their models they looked at objects of given
mass, and shape moving at some velocity striking the rail to determine an
optimal design including the composition of beams themselves, where to
drill holes to attach the rails, how to set them in the ground, etc., all
based on an assumption that all of the beam were identical for all know and
measurable (hopefully) parameters. They run the models and determine that
the rail SYSTEM will absorb some amount of energy which would prevent the
moving object from impacting a tree head on, while also not being just
another "TREE". But.... Even among 10, 6-foot rail posts cut from the
same 60ft beam; there are metallurgical differences and/or other flaws that
could affect performance of each individual post. (Hopefully small, but
each post will be different to a degree dependent on the quality control.)
After cut to post length, the holes are drilled for the bolts to attach the
rail, (pretty precise but not perfect) and each is eventually anchored in
the ground one at a time. Thus each post-system is a bit different, and in
some there may be significant differences (flaws) not found because the
quality assurance testing also assumes that for all practical purposes the
entire 60-ft beam from which they were cut is the same. So the question
is, what might we learn from running the crash models with a model in which
each post system (including the quite variable way it was set into the
ground were modeled individually using "population" (adjective) modeling. I
want to answer the question, 'what is the likelihood of a post system not
yielding as the design intends thus becoming a 'tree' that kills the family
instead of a shock absorber. I suspect that would fit as population
modeling. ?????
2. Not to overdo the adjective (maybe adverb) vs. noun thing but.... The
noun answer to me is what I would expect from a layperson reading only the
headline and first sentence of a newspaper article on population modeling.
(You guys are picking the term and there are downsides to labeling a new
construct of any kind with a couple commonly used words.) But Olaf's
short answer "noun", presumably naming the object of the modeling did
surprise me a little. So this naive observers thinks that now I do not
understand even though I asked the question. I agree that linguistically
his answer makes perfect sense but it raised the following: it suggests
that 'population modeling' is nothing new. Social scientist with out math
mentally modeled "populations' to write books or at least described
population behavior maybe before numbers existed and have done a lot of
work modeling the behavior of "populations = groups" of people described as
having and/or not having certain measurable (I hope) characteristic that
qualified them as a member of a group defined by those characteristics, or
a non-member. And then they did that with mathematical models using paper
and slide rules and 10 key calculators. So yes, I would call that
"population modeling". However, I was attracted to observe the emergence
of this population modeling group by people who do what I think most IMAG
people do, i.e. use "high performance" computational tools to increase the
degree of detail possible for building models.
Now my question is, is there some level of granularity characteristic
within the construct of population modeling that makes the modeling of a
population DOING 'population (adverb/adverb) modeling as different than
what can be done with 'common' vs. HP computational methods/tools? If so,
there may be some risk of calling the KIND of modeling you (collectively
for now) are calling population (a common word) modeling which could be
misinterpreted as the objects of the model when (if) you are really wanting
to bound the description of a METHOD(S) for modeling.
NEW TOPIC (sort of) If there really is no documented 'definition' to
describe PopMod and distinguish it from non PopMod modeling, those coming
forward in response to this call for PopMod'ers who believing that whatever
they are doing is an example will be the ones to define for posterity. To
protect your concept of the construct from abuse (which could give it a bad
name someday), your description (subject to evolutionary expansion over the
years) will need to be clear.
As a not quiet so naive cognitive science type, I suggest you consider the
following: to be useful an indiviual's concept of a named construct must
allow them to determine whether or not any potential instantiation of the
construct is or is not an example of the original construct. In the
instructional design world we teach concepts by presenting example and 'non
examples'. The degree of refinement at the margins between the example
which are included in the construct and the non-example which may on the
surface appear to be within, but are actually not example of, in this case
the construct population modeling. So consider finding some real, and/or
creating some hypothetical examples and non-examples of "population models"
(5-6 of each) with relatively simple one paragraph descriptions and putting
them into the example or non-example baskets. Some kind of descriptive
format for the exemplar models that provided a way to briefly address
characteristics that are most germane to classifying them as examples or
non-examples would be very helpful both to your own thinking about what
distinguish PopMods from other kinds of models and for sharing the examples
with others in 'elevator speech' time. Play with them. Move them around
modify them, think about what might justify changing which basket they
belong in; and when you have some general agreement, use the experience to
write a 1-2 paragraph description of what PopMod is. Send the description
to me and send me the 10-12 one-paragraph descriptions of the models from
the example, non-example baskets in random order to see if,after I read you
description of the construct PopMod, I can place each example of a model
inscriptions into the correct PopMod or Non PopMod basket. If I can come
pretty close I will be happy to pass the exercise along to some of my quite
more sophisticated M&S friend as an exercise followed by solicitation of
their questions or suggestions.
John
.
On Sat, Jan 17, 2015 at 5:06 AM, <popmodwkgrpimag-news-request at simtk.org>
wrote:
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> Today's Topics:
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> 1. Re: Population modeling definition (Jacob Barhak)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Fri, 16 Jan 2015 04:07:08 -0600
> From: Jacob Barhak <jacob.barhak at gmail.com>
> Subject: Re: [Population Modeling] Population modeling definition
> To: Talitha Feenstra <talitha.feenstra at rivm.nl>
> Cc: popmodwkgrpimag-news at simtk.org
> Message-ID:
> <CAM_y+3S_D1e1GhKA_8C8zvTeijA2_3nEupq61Jx1h-=
> s6mmGAA at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> Hi Talitha, Hi John, Hi Olaf, Hi Steve, Hi Stephan, Hi Al, and greeting to
> all others who have not participated yet.
>
> You have contributed thoughts to this discussion. I would like to point to
> two issues I see and add a third issue to the discussion
>
> 1. Dictionary like definition:
> John and Olaf are trying to define the term like a dictionary. In this
> perspective, I myself would interpret population as: "A collection of X"
> where X can change as Madhav suggested before. It is probably a noun
> describing plurality of X.
>
> 2. Definition by Models included:
> However, perhaps a more interesting discussion is what kind of models fall
> into our category. I recall Al and Steve trying to include Markov models,
> while Talitha and previously Stephan are excluding Markov Cohort models
> from falling within our definition of population modeling. This is to the
> best of my understating and I am surprised that Talitha suggested a strict
> definition since she some of her work is Markov model based.
>
> What would you all feel about including Markov models within population
> modeling only if they stratify the cohort by age, gender, and/or other
> parameters. And non stratified models will define these as cohort models
> outside population modeling?
>
> 3. Modeling of individual uncertainty
> This is another question. Would we consider description of uncertainty of
> parameters in an individual within our population modeling group? For
> example, does defining distribution of height of a person by mean,
> variance, and distribution function fall into our category? After all we
> are modeling a single entity from information derived from a population. I
> would say yes, especially if the information is extracted from a population
> that we can name. But what about correlation between anthropometric
> features such as defining the mean ratio between height and arm length as
> one number? Will one number be sufficient to call it population modeling
> or do we need a distribution? I would say if the number is associated to a
> population cohort then perhaps, and defiantly yes if we have several
> numbers associated with different population cohorts.
>
> I am interested to learn more what others think of those questions. I hope
> others will join this discussion.
>
> Jacob
>
>
>
>
>
>
>
>
>
>
> On Tue, Jan 13, 2015 at 3:25 PM, Talitha Feenstra <
> talitha.feenstra at rivm.nl>
> wrote:
>
> > Dear all,
> >
> > Following up on the definition discussion.
> >
> > I would suggest that the structure of the model (state transition, or
> DES,
> > or agent-based, or whatever) is not so important for the question whether
> > or not a model is a population model.
> > More important seems that it reflects a "population". That is, rather
> than
> > simulating a cohort of say 1000 people, it contains information on a
> > population's epidemiology and demography. This may or may not include
> > birth,and migration, and almost always includes mortality. This would
> then
> > indeed exclude Markov cohort models, but more due to the cohort aspect
> than
> > for their lack of modeling heterogeneity.
> >
> > However the examples presented go very broad and also include populations
> > of animals and even nonliving objects. Especially the latter gets
> confusing
> > to me, how to distinguish between what I knew of as "agent-based
> modeling"
> > which is a model structure, and "population modeling" ?
> >
> > kind regards, Talitha Feenstra
> >
> >
> > TL Feenstra, PhD
> > health economist
> > RIVM, Centre for Nutrition, Prevention and Health Services Research
> > Po Box 1
> > 3720 BA Bilthoven
> > *31 30 274 4387 (mon)
> > * 31 6 1186 87 60
> > UMCG, dept of epidemiology
> > PO Box 30.001
> > 9700 RB Groningen
> > *31 50 361 5110 (tue/thu/fri)
> >
> > -----popmodwkgrpimag-news-bounces at simtk.org wrote: -----
> > To: popmodwkgrpimag-news at simtk.org
> > From: Stefan Scholz
> > Sent by: popmodwkgrpimag-news-bounces at simtk.org
> > Date: 01/07/2015 10:58PM
> > Subject: Re: [Population Modeling] Population modeling definition
> >
> >
> > Hello all,
> >
> > I think the definition hits the broad subject really well. Maybe I am
> > seeing too much through the eyes of a health economist, but I would draw
> > the line of population models right after (cohort) markov models. In my
> > opinion mostly all of those cohort models ignore patient heterogeneity
> and
> > focus more on the disease rather than the population. On the other hand I
> > would say that "Individual Sampling Models" and DES as presented by Al
> > Chrosny and Jon Karnon do incorporate patient heterogeneity and should be
> > presented by the term "population model". So maybe we can draw the line
> > between cohort and individual Markov models.
> >
> > Best regards,
> > Stefan
> >
> >
> >
> > On 07.01.2015 22:17, Jacob Barhak wrote:
> >
> > Hello All,
> >
> > There is a growing demand to define the term population modeling. This
> > need is visible in some recent personal communications.
> >
> > This post will try to bring some quotes from different people who try to
> > define it during conversation. I intend to use some of this in the paper,
> > so I am bringing it to the list first to get opinions of more people.
> >
> > So here are key quotes:
> >
> > Sergey Nuzhdin USC:
> >
> > "we are doing lots of population / quantitative modeling, and i would
> love
> > to get engaged in human community;
> >
> > but so far, our efforts have been in Drosophila and plants"
> >
> > John Rice - Society for Simulation in Heathcare (SSiH) government
> > relations vice chair:
> >
> > "Sergey, perfect! I want to learn about PopMod for non human sciences
> > and engineer applications. If we had a population of trees in a forrest,
> > in stead of a generalized collective description. Could we predict the
> > course of a forrest fire better? Only beginning to think about that,
> then
> > here you are, modeling a populations of plants."
> >
> > Sergey replying:
> > " you are right, John, precisely what we are doing (among other things);
> >
> > how to predict collective properties from individual ones;
> >
> > there is plenty done about it when the subjects are homogeneous, and very
> > little when heterogeneous;"
> >
> > Madhav Marathe - Virginia Tech:
> > "The population modeling group is intended to be broad. Ofcourse making
> it
> > way too broad might make it harder for a cohesive conversation but we can
> > see how it plays out. I am calling this population of things; it appears
> > things is the best word I can use to keep the intended generality. We
> have
> > studied cells, wireless devices, people and animals in the past for
> > instance."
> >
> > It seems that the above discussion matches the ad hoc definition we
> > reached at the IMAG meeting at the NIH:
> >
> > "Modeling a collection of entities with different levels of
> heterogeneity"
> >
> > We reached this definition quickly and it was a broad consensus.
> > However, others on the list may want to discuss this definition and offer
> > alternatives.
> >
> > For example Markov models address populations mostly as time series and
> > seldom consider differences between individual entities, yet I would
> still
> > include Markov models under the umbrella of population modeling. It is a
> > difficult fit to the above definition unless hetrogeneity among states is
> > considered within time.
> >
> > I would appreciate your thoughts and will try to incorporate those in the
> > paper.
> >
> > Jacob
> >
> >
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--
"Where there is much desire to learn, here of necessity will be much
arguing,
much writing, many opinions; for opinion in good men is but knowledge in
the making."
John Milton (1608 - 1674)
Cellular 757 318 0671
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