Stock-Flow Model
Updated 2026-08-15
INTRODUCTION
English translation pending.
CORE DEFINITION
From system dynamics, a stock is a quantity that accumulates in a system, such as reservoir level, brand reputation, or knowledge, while a flow is the rate at which that stock rises or falls. The bathtub image makes the distinction concrete: the water level is the stock, and the tap and drain are the flows. The qualification is that stocks change with delay, so a large flow takes time to move the level and the level can keep falling after the inflow stops.
SCAFFOLDING EFFECT
Reduce cognitive load
- Use Level Versus Rate: separate the accumulated state from the rate of change when diagnosing a system. - Use Delay Accounting: allow for the lag between changing a flow and seeing the stock respond.
Anchor fast decisions
Because a stock integrates its flows over time, the current level reflects the whole history of inflows and outflows rather than the present rate. This is why a system can look healthy while its stock is draining, and why interventions on flows take time to appear in the level.
MINIMUM ACTION
In progress 0/1Practice this model in one real situation:
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Source support: Explicit
- en.wikipedia.orghttps://en.wikipedia.org/wiki/Stock_and_flowverified
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