edVirtus Reference

What Are Reference Modes and Behaviour-Over-Time Graphs?

Reference Modes: Defining the Dynamic Behaviour a Model Must Explain

A reference mode is a description of the behaviour over time that motivates and guides a system dynamics study. It may be presented as historical data, a qualitative graph, a verbal pattern, or several plausible future trajectories for important variables.

Behaviour-over-time graphs place time on the horizontal axis and a variable of interest on the vertical axis. They direct attention away from isolated events toward patterns such as exponential growth, goal seeking, oscillation, overshoot, decline, or changing variability.

A reference mode helps define the modelling problem. Saying that a service is under pressure is less precise than showing how demand, capacity, waiting time, and outcomes have changed and identifying the period and behaviour requiring explanation.

The graph may distinguish observed, expected, feared, and desired trajectories. It need not imply precise numerical forecasts. Its role is to clarify what the model should reproduce or illuminate and to expose differences among stakeholder expectations.

Reference modes also constrain model evaluation. A model that fits one data point but cannot generate the characteristic pattern has not explained the dynamic problem. Conversely, reproducing a curve is insufficient unless the underlying structure and assumptions are credible.

Used early, reference modes keep model development focused. They provide a bridge between the real-world concern and the dynamic hypothesis, helping analysts decide which stocks, flows, feedback loops, delays, and boundaries are relevant.