Classification of

Study Guide #4 Classification of
Evidence

Methods of Classification

Physical v. Nonphysical
Known v. Unknown
Class v. Individual

Physical V. Nonphysical Evidence

Physical evidence includes objects and people
Nonphysical evidence includes testimony, results of tests such as polygraph

Known V. Unknown Evidence

Must consider context
Determined before the evidence is analyzed
Question: do we know where this evidence came from?

Class V. Individual Evidence

Identification of evidence
Process of putting in smaller classes of objects or persons

Class V. Individual Evidence

Individual evidence can be put in class of one
Implies that there are unique characteristics
Class evidence cannot be put in a class of one

Class V. Individual Tests

Class tests help identify evidence
Individual test puts evidence in class of one
Always a comparative test

Identification V. Comparison

All evidence is identified
If known exists, evidence may be compared
Only method of individualization is by comparison of known

Controls

Positive control

Known sample which is expected to respond positively to test

Negative control

Known sample which is expected to respond negatively to test

False Positives and Negatives

False positive
Results of test are positive when they should be negative
Often caused by failure to perform negative control test

False negative
Results of test are negative when they should be positive
Often caused by failure to run positive control test

Presumptive V. Confirmatory Test

Presumptive test permits only qualified conclusion
Confirmatory test permits definitive conclusion