8127/frame/fm

1.
The Necessity of Providing an Assessment of the Strength 
of the Inference
Without some expression of the strength of the source determination, the
results of an examination are virtually worthless and potentially misleading.
This was expressed most emphatically about DNA evidence in the first report
of the National Research Council (1992), and can be generalized to all foren-
sic evidence.
Some practitioners argue that a mere description of the tests performed
and the results obtained fulfills the responsibility of the forensic scientist. For
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instance, some reports on biological evidence merely list the results of a battery
of genetic marker tests performed on a physiological fluid stain and a reference
sample, leaving it to the reader to see that the results are the same. Even if
this similarity is highlighted in the report, a discussion of its meaning is
frequently lacking. This leaves the lay reader in the unenviable position of
having to determine the meaning of the similarity. This, we contend, is a
disservice to the public. The forensic scientist is in the best position to com-
ment on the strength of the evidence. For potentially individualizing evidence,
this is simple. In fingerprint, toolmark, and physical match examinations, the
strength is typically expressed as an 
opinion
that the evidence and reference
share a singular common source. Because the strength of class evidence is
more difficult to determine and support, such an expression is less commonly
provided. Results of an evidence examination presented without a statement
about the strength of the relationship of the evidence to the putative source
is an abdication of the responsibilities of the competent examiner. No one is
better able to comment on the strength than the forensic scientist.