Two essential model-building activities are verification and validation. Unfortunately these
two terms are often used interchangeably, which leads to confusion.
Verification and validation involve two distinctly different types of activities
but which are frequently inseparable when it comes to system
dynamics modelling. Our focus here is on verification. Simply put,
verification helps us answer the question: "Are we building the
In system dynamics modelling, verification is all about ensuring
that the governing business rules have been correctly coded, that
the structure in which those rules operate results in correct
and sufficient replication of the reference modes of behaviour identified
in an earlier stage (and specified as requirements for the
model we are building).
There are a variety of tests which
might be conducted in the process of verifying a module
or model. These include logical tests, extreme-value tests, and mass-balance
tests. Mass-balance tests are designed to assure that physical flows
do not violate the basic requirement for physical flows into
a module, sector or model either accumulate or flow out.
Mass-balance must be assured during every time-step of every simulation
The method used to test the mass-balance of a Powersim
Studio model is explained and demonstrated in .
The corresponding Powersim Studio 2005 model is .