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Thinking in Diagrams

Chapter 5: Delays, External Drivers, and Competing Loops

Drafted for Aryeh's edit.

For chapter 5: Delays, External Drivers, and Competing Loops

Timing

Section titled “Timing”
  • Reading the chapter: about 9 minutes, its 1,415 words of prose at 150 words a minute. Not counted in those minutes: 2 figures, 1 pair, 2 understanding checks, the reading exercise and the exercises.
  • A session: 50 minutes, the exercises set for it. (estimate)
  • Afterwards: 95 minutes, the exercises set for then. (estimate)

Common misreadings

Section titled “Common misreadings”
  • An external driver wired into a loop. In the bad diagram, regional population is marked as an external driver with an effect running into it from homes on the outskirts, so B3 runs through it; the lab’s check reports it, naming the effect.
  • A variable made external by where it sits or who decides it. In the understanding check about homes on the outskirts, the homes are on the outskirts, outside the town and developers decide what gets built are wrong choices; in the reading’s first question, so is target level of prescription: government sets it. An external driver is one nothing drawn changes.
  • Loop dominance read as permanent. Dominance is which loop drives behavior at a given time. In the understanding check about the road five years on, B1 never moved travel time: widening did nothing reads the loops leading in the fifth year back into the first.
  • Delays left out. Booth Sweeney and Sterman (2000) found students at an elite business school, new to system dynamics, understood time delays poorly. In the reading’s third question, a delay belongs on quality of help → mistakes, giving R1 time to dominate; CL 06’s brief requires two delays.
  • A loop diagram read as separate effects, each judged alone. In the chapter’s Common misreading, lanes on the main road → travel time, judged alone, means a shorter drive; the drive lengthens again through the loops it sits in.

Exercises to set

Section titled “Exercises to set”

The session goes from two loops with a boundary and an external driver, through the published loops of compliance, to policy resistance; the archetype in CL 08, viewpoints, a full model and the case come afterwards.

For a session

Afterwards

Sources

Section titled “Sources”