Quote:
Originally Posted by Rain Man
Interesting. On population projections of humans, I've typically used either a simple exponential model (short-term only), or a ... what's it called. P2=P1*e^(-kt). That one. Can't remember the name. For population growth they tend to work pretty well because the growth rates are relatively small numbers.
What's Z in your third model?
I know this firm, and they have no ability to do projections at all. In fact, all they were trying to do is say that the population has grown X percent over a 7 year period, and they couldn't even do that.
This one particular firm is a joke. They don't do research and have no researchers on staff, but if a client wants it they'll make all sorts of claims and take their money. And then they do stuff like the calculations above. And don't even get me started on their surveys. I wish my business had some sort of entry requirements.
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P2=P1*e^(-kt) is the integrated form of the geometric model. Also called a first order model. I would also call it an exponential growth model.
In the third model, Z is the "maximum" population that the resources in the area would support. That model approaches Z asymptotically.
I always tell my students (we need to do population projections to build water and wastewater plants that have to have a useful life of up to 50 years) that population projections are black magic and to get someone else to do them.
I use the following in-class example. Rank the following cities in terms of their 1910 and 1960 populations, and describe the driving forces for the change in population over that time interval:
Providence, RI
Detroit, MI
Miami, FL