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4.
Definition of Association
In attempting to refine our understanding of association in forensic science,
we have established several points:
1. The law requires that evidence be relevant; the existence of the evi-
dence must make the actuality of some principal fact more or less
probable than it would be without the evidence.
2. Potentially individualizing physical evidence is circumstantial evi-
dence; an inference is required to connect the evidentiary fact with
the principal fact in question.
3. Source determination is usually not relevant per se; an inference is
required to make it relevant.
4. The inference required to render a source determination relevant is
that of contact between two objects.
5. Inferences depend on assumptions and other information; the same
physical evidence may support several competing inferences, depend-
ing on the assumptions and available information.
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Principles and Practice of Criminalistics
We summarize these points into a definition of association:
Although the term 
 
association
has, up to now, been poorly defined, it is
potentially more descriptive than the term 
 
interpretation
. We choose to retain
association to characterize this aspect of the paradigm. We also define the
phrase 
 
inference of contact 
as a synonym for association.
 
5.
Associating Two Objects through an Inference of Contact
Criminalists examine potentially individualizing evidence with the (usually
unarticulated) goal of providing information about the proposition of con-
tact. Source determination is only the first step in the inferential chain that
leads to an inference of association. Keeping this thought in mind during
examination will help the analyst define the limitations of the evidence, and
will force an explication of the assumptions that must be made to support
an inference of contact.