Method guideSystems Thinking

Stock and Flow Diagram

A practical method guide: clarify prerequisites and materials, understand the complete process, and look up outputs, pitfalls, and stop criteria.

ComplexityHigh

Time2-6 h

Participants1-6

FormatWorkshop + async

MaturityEstablished

Plan the work

Prerequisite

What needs to be finished first

Complete firstClear working frame

Define the boundary, time period, stock quantities and their measurement units.

Without a bounded question or checkable evidence, the result will be unclear.

Preparation

What needs to be ready before start

Materials

Boundary, available time series, units list, domain rules and a modeling tool.

People / roles

Domain owners · system dynamics modeler · data specialist; review every quantity and assumption together.

Pre-read

Choose materials, data access and participants to fit the research or decision question.

Time needed

2–6 hours for a small conceptual model; calibration and simulation are separate.

Setup

Open the method-specific structure. Fictional examples are for orientation only; keep the blank worksheet separate from actual findings.

Core question

The one question this method answers

How do inflows and outflows change stocks over time?

Flow

Phases with goal, actions, output and pitfall

Stock-and-flow diagrams show accumulation, delay, and capacity as behaviour over time. Stocks are state quantities and flows are rates of change per unit of time.

Stock and Flow Diagram working record

Fictional example

Method-specific prompts and a fictional worked example; template prompts remain empty.

Define stocks and units

Define each stock with unit and opening balance.

**Boundary:** Service cases from arrival to resolution.

Add inflows and outflows

Balance each stock as opening value plus inflows minus outflows.

**Stock:** Open cases, unit cases; fictional opening stock: 10 cases at the start of the week.

Model rates and delays

Write rate rules and document evidence, assumptions and delays.

**Inflows:** New cases: 8 cases/week for one week.

Test behavior and scenarios

Test plausible behavior; report calibration and limits.

**Outflows:** Resolved cases: 6 cases/week over the same week.

The guide explains stock-flow units and consistency: stocks use quantity units, flows use quantity per time and change stocks.

System Dynamics Learning Guide

1
Stocks
Define stocks and units
Goal
Define each stock with unit and opening balance.
Inputs for this step
- Define the boundary, time period, stock quantities and their measurement units.
- Boundary, available time series, units list, domain rules and a modeling tool.
Actions
- Name accumulated quantities, units, starting value and reference date; set the system boundary.
- Record Stocks with units and initial value with its evidence status, source or open verification need.
Output
Stocks with units and initial value
Stocks with units and initial value
Quality check
Can the quantity be measured at a point in time?
Pitfall
A throughput event is drawn as a stock. Separate accumulation from change rate.
Timing: About 10–20 minutes; schedule data or clarification work separately.
2
Flows
Add inflows and outflows
Goal
Balance each stock as opening value plus inflows minus outflows.
Inputs for this step
- Stocks with units and initial value
- Boundary, available time series, units list, domain rules and a modeling tool.
Actions
- Connect each flow to a stock and express it in the stock unit per time unit.
- Record Conserved flows with consistent rate units with its evidence status, source or open verification need.
Output
Conserved flows with consistent rate units
Conserved flows with consistent rate units
Quality check
Does flow unit equal stock unit per time?
Pitfall
A flow acts without changing a stock. Write the balance for every stock.
Timing: About 10–20 minutes; schedule data or clarification work separately.
3
Dynamics
Model rates and delays
Goal
Write rate rules and document evidence, assumptions and delays.
Inputs for this step
- Conserved flows with consistent rate units
- Boundary, available time series, units list, domain rules and a modeling tool.
Actions
- Describe rules that influence rates; mark delays and causal assumptions.
- Record Rules, parameters and delays with its evidence status, source or open verification need.
Output
Rules, parameters and delays
Rules, parameters and delays
Quality check
Are mechanisms and units checkable?
Pitfall
Correlation is coded as a causal law. Separate evidence, assumed function and plausible delay.
Timing: About 10–20 minutes; schedule data or clarification work separately.
4
Behavior
Test behavior and scenarios
Goal
Test plausible behavior; report calibration and limits.
Inputs for this step
- Rules, parameters and delays
- Boundary, available time series, units list, domain rules and a modeling tool.
Actions
- Check units, edge cases and historical behavior; simulate only with transparent assumptions.
- Record Consistent model and scenario questions with its evidence status, source or open verification need.
Output
Consistent model and scenario questions
Consistent model and scenario questions
Quality check
Are values, period and model limits clear?
Pitfall
A simulation is presented as a forecast. State calibration, uncertainty and limits.
Timing: About 10–20 minutes; schedule data or clarification work separately.

Artifact

What comes out at the end

Sketch: what the artifact looks like

Stock and Flow · SystemdynamikBestände, Zu- und Abflüsse sowie Feedback auf Raten als Systemdynamik sichtbar machen

Form

Versioned record of question, evidence, result, uncertainty, owners and next review date.

Versioning / ownership

Track date, scope, sources, assumptions and changes; assign an owner and review for ongoing practice or initiatives.

Tool alternatives

Paper and pens
Whiteboard or simple table

stock-and-flow-diagram-working-template.md

Plan a session or initiative to match the actual scope of work.

Stock and Flow Diagram: Worksheet

Question

To be confirmed

Desired outcome

To be confirmed

Scope

Prepare the full method Time: 2–6 hours for a small conceptual model; calibration and simulation are separate.

Complete this worksheet on paper or in your own document during the work.

Preparation for this scope

Method setup

Materials: Boundary, available time series, units list, domain rules and a modeling tool.
Roles: Domain owners · system dynamics modeler · data specialist; review every quantity and assumption together.
Advance information: Choose materials, data access and participants to fit the research or decision question.
Overall time needed: 2–6 hours for a small conceptual model; calibration and simulation are separate.
Setup: Open the method-specific structure. Fictional examples are for orientation only; keep the blank worksheet separate from actual findings.

Prepare for the work steps

Stocks: Define stocks and units

Define the boundary, time period, stock quantities and their measurement units.
Boundary, available time series, units list, domain rules and a modeling tool.

Flows: Add inflows and outflows

Stocks with units and initial value
Boundary, available time series, units list, domain rules and a modeling tool.

Dynamics: Model rates and delays

Conserved flows with consistent rate units
Boundary, available time series, units list, domain rules and a modeling tool.

Behavior: Test behavior and scenarios

Rules, parameters and delays
Boundary, available time series, units list, domain rules and a modeling tool.

Stock and Flow Diagram working record

Define stocks and units

Define each stock with unit and opening balance.

...

Add inflows and outflows

Balance each stock as opening value plus inflows minus outflows.

...

Model rates and delays

Write rate rules and document evidence, assumptions and delays.

...

Test behavior and scenarios

Test plausible behavior; report calibration and limits.

...

Blank worksheet contains prompts only, with no example data.

System Dynamics Learning Guide

Stocks: Define stocks and units

Expected artifact: Stocks with units and initial value

Stocks with units and initial value

Entry:

...

Can the quantity be measured at a point in time?

Flows: Add inflows and outflows

Expected artifact: Conserved flows with consistent rate units

Conserved flows with consistent rate units

Entry:

...

Does flow unit equal stock unit per time?

Dynamics: Model rates and delays

Expected artifact: Rules, parameters and delays

Rules, parameters and delays

Entry:

...

Are mechanisms and units checkable?

Behavior: Test behavior and scenarios

Expected artifact: Consistent model and scenario questions

Consistent model and scenario questions

Entry:

...

Are values, period and model limits clear?

Open questions and next steps

...

Method guide: https://methodatlas.meierhoff-systems.de/en/methods/stock-and-flow-diagram/run-sheet

Example output

Concrete filled scenario, fictional example

Fictional example for orientation. Counts and timings describe this case and are not universal requirements.

stock-and-flow-diagram-beispiel.md

Concrete filled scenario, fictional example

Fictional example: service queue

Boundary: Service cases from arrival to resolution.

Stock: Open cases, unit cases; fictional opening stock: 10 cases at the start of the week.

Inflows: New cases: 8 cases/week for one week.

Outflows: Resolved cases: 6 cases/week over the same week.

One-week balance: 10 cases + (8 cases/week × 1 week) − (6 cases/week × 1 week) = 12 cases at period end.

Hypothesis: Onboarding may affect resolution rate after a delay; check the mechanism and lag with data or process knowledge.

Limit: Values are fictional and only illustrate the balance. Without valid rates and time series, the model is not a forecast.

Pitfalls

Recognize symptoms and steer against them

Quick overview, the full text is in the matching phase in the flow

Define stocks and unitsA throughput event is drawn as a stock.View in phase
Add inflows and outflowsA flow acts without changing a stock.View in phase
Model rates and delaysCorrelation is coded as a causal law.View in phase
Test behavior and scenariosA simulation is presented as a forecast.View in phase

Stop criteria

When to pause, resolve prerequisites, or choose another approach

If a stock has no unit, a flow is unconnected, or time bases conflict, resolve the balance first. Do not simulate quantitatively without defined rates, checked data and sensitivity analysis.

Where to go next?

Systems Thinking

System Dynamics Simulation

Simulates the consistent model across several parameter scenarios.

Business Strategy

Scenario Planning

Uses the model's scenario questions for a broader look at possible futures.

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