thinking in systems (Meadows)

 
Donella H. Meadows, Edited by Diana Wright, Thinking in systems     [ ]

p.103
Jay Forrester used to tell us, when we were modeling a construction or processing delay, to ask everyone in the system how long they thought the delay was, make our best guess, and then multiply by three. (That correction factor also works perfectly, I have found, for estimating how long it will take to write a book!)

p.104
Here are just a few of the delays we have found important in include in various models we have made:

    • The delay between catching an infectious disease and getting sick enough to be diagnosed──days to years, depending on the disease.
    • The delay between pollution emission and the diffusion or percolation or concentration of the pollutant in the ecosystem to the point at which it does harm.
    • The gestation and maturation delay in building up breeding populations of animals or plants, causing the characteristic oscillations of commodity prices: 4-year cycles for pigs, 7 years for cows, 11 years for cocoa trees.8 
    • The delay in changing the social norms for desirable family size──at least one generation.
    • The delay in retooling a production stream and the delay in turning over a capital stock. It takes 3 to 8 years to design a new car and bring it to the market. That model may have 5 years of life on the new-car market. Cars stay on the road an average of 10 to 15 years.

p.187
Appendix

System Definitions: A Glossary
(selected list, for the complete list, see book)

Archetypes: common system structures that produce characteristic patterns of behaviour.

Bounded rationality: the logic that leads to decisions or actions that make sense within one part of a system but are not reasonable within a broader context or when seen as a part of the wider system.

p.188
System: a set of elements or parts that is coherently organized and inter-connected in a pattern or structure that produces a characteristic set of behaviour, often classified as its “function” or “purpose.”

     (Thinking in systems : a primer, Donella H. Meadows, Edited by Diana Wright, sustainability institute, 2008, QA 402 .M425 2008, )
   ____________________________________

  pregnancy : 9 month to give birth to a baby 
   ____________________________________

    • The gestation and maturation delay in building up breeding populations of animals or plants, causing the characteristic oscillations of commodity prices: 4-year cycles for pigs, 7 years for cows, 11 years for cocoa trees.8 


The shorter oxford economic atlas of the world

prepared by the economist intelligence unit 
and the
cartographic department of the clarendon press 

first edition, 1954
second edition, 1959
1965
copyright Oxford university press 1965

Printed in Italy by Corbellini, Milan 

3rd edition
reprinted  1966

p.48
   Pigs.   Pigs are normally kept on mixed farms where they can be fed cheaply on farm by-products or coarse grains.  In Denmark, for example, the Landrace pig, which has been carefully bred to produce bacon economically, is fed on barley and the skim milk left over from butter making.  Pigs eat less and fatten more quickly if warm and dry, and this helps to cover the high capital cost of the buildings which are essential for housing them in the winter in northern countries. 
   It takes about four months to fatten up a pig for pork, and rather longer for bacon.   The breeding cycle can be completed in six months, and pigs normally litter 8─10, so it is possible to increase the supply of pig meat rapidly.  This cause big cyclical fluctuations, scarcity of pigs at high prices alternating with abundance of pigs at low prices.  
   ____________________________________