## Demographic Profiles and Health Care

"Jim Hines"
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Joined: Fri Mar 29, 2002 3:39 am

### Demographic Profiles and Health Care

You want to use an "aging chain". An aging chain is simply a several
material delays hooked together. (A material delay is a decay with an
input - probably what youre using right now). So the input to the first
stock is whatever your current input is (births?), the output of the first
stock is the stock divided by the average time in that stock. The input to
the second stock is the output from the first stock, etc. The more stocks
you put together, the more the output will look like the second part of an
"n" (Assuming that all stocks except the first start at zero). The sum of
the delays will equal the average residence time in the chain; the delay for
any one stock will equal the average residence time in that stock. So you
could have three stocks: Young people, Middle aged people, and old people.
If you are young until thirty-five, the first time constant would be 35
years. If you are middle aged until you hit sixty, the second stock would
have a time constant of 25 years. If the average life expectancy of a 60
year old is to live until 90, the third time constant would be thirty years.

Jay Forresters rule of thumb is that a third order delay is usually
sufficient for the delay to communicate the proper dynamics to the rest of
the model. Jim Lyneis tells me that to get an "echo" (e.g. an upsurge in
births when the baby-boomers have babies) you need at least a sixth-order
delay.

Regards,
Jim Hines
MIT and LeapTec
jhines@mit.edu

"Forrester, Nathan"
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Weishuang Qu
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Bill Braun
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Joined: Fri Mar 29, 2002 3:39 am

### Demographic Profiles and Health Care

>normally death rate would be defined as the number of deaths/population. in
>itself this is not time dependant, but a constant representing the nature of
>the environment being examined (ie how good the health care is, the
>environmental hazards etc).

Ive struggled with this, as much a function of my mental model as one of
technical accuracy. Several issues, if discussed, would help with my
understanding.

One, if we assume that life expectancy is constant and the distribution of
chronic and acute illness across age/gender stocks is constant, then using
death rates as a fraction of the population seems reasonable. What happens
if any or all of those change? Are the potential implications (moderated by
the dynamics the population model is driving) material to the insights the
overall model reveals?

Two, (correspondingly) social norms reflective of shifts in culture mix
could materially affect birthrates. For example, european,
african-american, hispanic, pacific rim, balkan, (name your culture) etc.
peoples have different attitudes toward pregnancy (family size, conditions
under which it takes place, etc). Assuming these attitudes remain constant
but the culture mix changes, are the implications likewise material? If the
attitudes themselves change (one or more cultures raise or lower their
reproduction attitudes), does that further complicate the mix?

Third, what if a sudden epidemic occurs that disproportionately affects the
population based on age and/or gender and/or culture mix, etc., etc.

Is sensitivity germane to this discussion (admittedly more or less relative
to the dynamics the population model is affecting and being affected by)
and is selecting the number of stocks a critical decision in designing the
model?

Bill Braun
From: Bill Braun <medprac@hlthsys.com>

"geoff coyle"
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