Biological processes are either described mathematically
or in qualitative terms. The mathematical
description derives from scientific
investigations and its adequacy can be assessed
by computer simulations. Since the description is
already in mathematical terms, it can be modelled
easily. Examples are models of the blood
circulation or the depolarization of the heart.
When it is established that the model provides
a good representation of reality (for the purposes
in mind), a real life process can be evaluated
by comparing actual observations with
model predictions. Changes in the process are
detected as deviations from the theoretical predictions
(e.g. monitoring the EEG of a patient
to detect epileptic spikes by using a model that
simulates the background EEG). The model can
also be used to monitor therapeutic actions by
predicting outcome following an intervention.
Some models are not only useful for deteceing
changes in the process but also for determining
the reason that caused the changes.
Since biological models are formalized descriptions
of biological processes, they can be
implemented as programs. In a similar way,
physical processes can be modelled quite easily.
In radiotherapy for example, radiation protocols
are established by using physical knowledge. It
is possible to start from first principles. To reduce
computing time, however, approximations
based on experimental data are usually incorporated
in the model and used in the calculations.