Search found 27 matches

by Alan Graham
Fri Dec 03, 2004 5:18 pm
Forum: SD Mailing List Archive
Topic: Models and Science
Replies: 20
Views: 36518

Models and Science

Re: ""Modeling is not science..."" Sir Isaac and his later colleague Albert would disagree. cheers, alan Alan K. Graham, Ph.D. Decision Science Practice PA Consulting Group Alan.Graham@PAConsulting.com One Memorial Drive, Cambridge, Mass. 02142 USA Direct phone (US) 617 - 252 - 0...
by Alan Graham
Mon Nov 08, 2004 3:17 am
Forum: SD Mailing List Archive
Topic: The study of hurricanes
Replies: 8
Views: 11469

The study of hurricanes

On Hurricanes and SD: In the context of wondering which systems or problems System Dynamics is good for, I'd characterize those systems as the systems in which we can identify plausible aggregate quantities (those that will tend to behave as a single group, and thus characterizable by one or a small...
by Alan Graham
Fri Nov 05, 2004 7:00 pm
Forum: SD Mailing List Archive
Topic: Using models for Project Costing
Replies: 3
Views: 7865

Using models for Project Costing

Chariya, There's a reasonable set of references in my ""Beyond Project Management 101: Lessons for Managing Large Development Programs"" in the Project Management Journal 31(4) 7-18, 2000. The editors asked me to reduce it, so the work of Terry Williams at U. Strathclyde, David F...
by Alan Graham
Fri Oct 29, 2004 2:19 pm
Forum: SD Mailing List Archive
Topic: SD vs System Design Engineering
Replies: 2
Views: 6937

SD vs System Design Engineering

Re Joel's audience question on System Dynamics compared to System Design Engineering: The purpose of System Dynamics (SD) is enabling a correct choice of policy or strategy in a complex setting; the purpose of System Design Engineering, or equally commonly, just Systems Engineering (SE) is roughing ...
by Alan Graham
Wed Feb 04, 2004 8:58 am
Forum: SD Mailing List Archive
Topic: Using Statistics in Dynamics Models
Replies: 28
Views: 20828

Using Statistics in Dynamics Models

To perhaps reiterate Carolus Grutters point: This reasoning doesnt follow: Quote JJ.Lauble and Jim Hines : >> If you can >> prove A implies B with only a 5% chance of error. And, if you can prove that >> B is not true, then youve proved that A is not true with only a 5% chance >> of error. If I get ...
by Alan Graham
Sun Feb 01, 2004 1:09 pm
Forum: SD Mailing List Archive
Topic: Using Statistics in Dynamics Models
Replies: 28
Views: 20828

Using Statistics in Dynamics Models

Jim inquires as to the nature of "practical assumptions" that go into a FIMLOF-based analysis. To answer the immediate question: 1. "Practical" means that the assumptions match up well with the real-world situation youre trying to model. How do you make "practical" assu...
by Alan Graham
Fri Jan 30, 2004 3:03 pm
Forum: SD Mailing List Archive
Topic: Using Statistics in Dynamics Models
Replies: 28
Views: 20828

Using Statistics in Dynamics Models

Jim asks what I meant by the FIMLOF method being "rigorous and practical" "Practical": means you can use it (or approximations to it) with real problems. "Rigorous": Well its true that virtually every formal statistic method is mathematically rigorous in getting from it...
by Alan Graham
Wed Jan 28, 2004 10:19 am
Forum: SD Mailing List Archive
Topic: Periodicals portfolio models
Replies: 1
Views: 2656

Periodicals portfolio models

Arne-Helge asks about models of portfolios of (likely interacting) products of mixed characteristics, and optimizing resourcing for them. He can find an approach close indeed to his situation described in Graham and Ariza, "Dynamic, hard and strategic questions: using optimization to answer a m...
by Alan Graham
Tue Jan 27, 2004 2:40 pm
Forum: SD Mailing List Archive
Topic: Can SD models be validated without being run?
Replies: 38
Views: 27356

Can SD models be validated without being run?

Jim Hines asks whether theres a rigorous argument that statistical analysis can/cant be used in lieu of simulation to validate a model. This discussion chain seems to have been proceeding on the assumption that statistical methods can be applied independently of simulation. Except for some extraordi...
by Alan Graham
Thu Oct 16, 2003 12:02 pm
Forum: SD Mailing List Archive
Topic: Modeling Innovation Diffusion
Replies: 4
Views: 4709

Modeling Innovation Diffusion

All, I hesitate to respond to queries like this, as theres no appearance of appropriate effort. While I support collegial interchange, I dont support being an expensive substitute for individuals looking at the obvious sources--the half-dozen or more SD textbooks and the SD Review. Although this may...
by Alan Graham
Sun Jun 01, 2003 4:34 pm
Forum: SD Mailing List Archive
Topic: School quality related models
Replies: 5
Views: 4893

School quality related models

In the 1970s, Richard Foster at MIT did extensive modeling of school quality as it interacted with a larger urban system. The work extended the Urban Dynamics model with what I recollect to be a substantial elaboration with respect to school quality. With luck, this research is still available from ...
by Alan Graham
Wed May 07, 2003 8:30 am
Forum: SD Mailing List Archive
Topic: Law and Policy System Dynamics
Replies: 3
Views: 4147

Law and Policy System Dynamics

Grant, Three suggestions: 1) Prod David Andersen and George Richardson to compile a (likely multi-volume) book of their decades of public policy applications of System Dynamics. Barring that, Ill bet a Google search would turn up plenty. 2) Check out Jay Forresters Urban Dynamics, my and Louis Alfel...
by Alan Graham
Mon Apr 21, 2003 11:19 am
Forum: SD Mailing List Archive
Topic: Can system dynamics models "learn"
Replies: 46
Views: 33408

Can system dynamics models "learn"

Colleagues, John Stermans beer game example is also answering an important related question: SHOULD realistic system dynamics models of peoples decision-making learn? And the answer is (if one generalizes), not very often in complex dynamic systems. The laboratory experiment John describes is a cont...
by Alan Graham
Sun Apr 20, 2003 8:09 pm
Forum: SD Mailing List Archive
Topic: Can system dynamics models "learn"
Replies: 46
Views: 33408

Can system dynamics models "learn"

Colleagues, Theres a substantial literature on Adaptive Control, in which a control system adapts its feedback responses to, e.g. changing parameters or changing environment, i.e. dynamic systems that learn. For example, one implementation of an adaptive control system monitors real behavior and con...
by Alan Graham
Tue Apr 08, 2003 11:35 am
Forum: SD Mailing List Archive
Topic: Dynamics models of privatization using agency theory
Replies: 1
Views: 2286

Dynamics models of privatization using agency theory

Hi Rosa, For sure youll want to look at the description of privatization analysis at London Underground in Donna Mayo, Martin Callaghan and William Dalton, "Aiming for restructuring success at London Underground" (System Dynamics Review Volume 17 #2, 2001). The general approach in this and...
by Alan Graham
Tue Apr 01, 2003 8:53 am
Forum: SD Mailing List Archive
Topic: Models on Stress at Work
Replies: 6
Views: 5229

Models on Stress at Work

Hi Marcia, Have a look at: Cooper, Kenneth G. (1994). The $2,000 Hour: How Managers Influence Project Performance through the Rework Cycle. Project Management Journal, March 1994. He discusses workload- and overtime-related stress and its direct and indirect effects on technical (design and construc...
by Alan Graham
Fri Feb 21, 2003 4:32 pm
Forum: SD Mailing List Archive
Topic: attractivenss multiplier
Replies: 6
Views: 13182

attractivenss multiplier

Hi Daniel, As usual, there are at multiple approaches to modeling utility in dynamic models: 1. The traditional way is attractiveness multipliers that are the product of many input multipliers. Described in, e.g. Forresters Urban Dynamics or my (and Louis Alfelds) Introduction to Urban Dynamics, and...
by Alan Graham
Mon Feb 03, 2003 9:15 am
Forum: SD Mailing List Archive
Topic: Channel Systems
Replies: 5
Views: 5216

Channel Systems

Tim and other colleagues, People interested in sales channel design will likely find articles by myself and Carlos Ariza of interest. A version appears in the proceedings of the 2001 Atlanta SD conference, and a refined version should be coming in volume 1 of 2003 SDR. That work applies optimization...
by Alan Graham
Thu Oct 17, 2002 12:01 pm
Forum: SD Mailing List Archive
Topic: Limitations of System dynamics?
Replies: 10
Views: 20906

Limitations of System dynamics?

Trouble is, SD is an extremely malleable process -- at heart, its just the scientific method, with many potential tools and processes available. Effective SD engagements can look like everything from group facilitation to econometrics. In practice, the limitations that most often constrain applicabi...
by Alan Graham
Fri Jul 05, 2002 2:26 pm
Forum: SD Mailing List Archive
Topic: Representing constraints
Replies: 30
Views: 43684

Representing constraints

I have to raise two objections to some of the implications of the exchange between Mssrs. Palfreyman and Barry, based on some of the values traditionally espoused by the system dynamics community. John Stermans reply has touched on these, but Im compelled to amplify, as the majority of e-corresponda...
by Alan Graham
Tue Jul 02, 2002 4:54 pm
Forum: SD Mailing List Archive
Topic: Representing constraints
Replies: 30
Views: 43684

Representing constraints

This is a perfect example of model purpose having much to do with the formulation (even though in a domain the SD community isnt often paid to solve problems or teach in): For the classic piston-in-a-cylinder setup, with the piston position being changed in time horizons of seconds: represent volume...
by Alan Graham
Sun Jun 23, 2002 6:49 pm
Forum: SD Mailing List Archive
Topic: Models with Sectors and Multiple Authors
Replies: 11
Views: 15147

Models with Sectors and Multiple Authors

Jim, Niel, et al. Two broad areas of comment: my empirical guidelines for multi-author work at different phases of model maturity, and commonality with software development concepts. MULTI-CONTRIBUTOR WORK... ...based on a few less-than fun experiences and several good ones. The overall concept is t...
by Alan Graham
Wed Apr 10, 2002 12:28 am
Forum: SD Mailing List Archive
Topic: Questions for consultants roundtable at SD conference
Replies: 0
Views: 2711

Questions for consultants roundtable at SD conference

This years consultants roundtable at the SD conference will change the format from years past: Consultants will discuss questions solicited in advance. So what do people want to ask consultants in particular? What do academics most need to know about the realities of commercial model-building? What ...
by Alan Graham
Fri Jul 20, 2001 10:08 am
Forum: SD Mailing List Archive
Topic: The order of a system
Replies: 16
Views: 10656

The order of a system

sigh.... 1. The equation with sines may be a model, but its not a dynamic model. 2. The decoupled system is a second-order system thats indeed boring, but thats just for the particular policies and causal relationships choosen. Theres even a body of literature on how to design feedback systems so th...
by Alan Graham
Wed Jun 06, 2001 4:21 pm
Forum: SD Mailing List Archive
Topic: System Dynamics Certification
Replies: 12
Views: 9908

System Dynamics Certification

Well, the short description of the certification question is "tar baby": well all get stuck in it if we wrestle with it too much, at least coming at it simplistically. The reason? Most of the analogs to "certifications" in other fields I can think of have multiple prerequisites o...