Questioned (Q) Sample
Definition
A sample recovered from a scene, a person, or an object whose origin or relationship to a source is the subject of the forensic inquiry. The Q sample is what is being tested.
- Role
- Unknown-origin sample under test
- Compared against
- Reference or known (K) sample
- Applies to
- Trace, biological, chemical evidence
Common questions
What is the difference between a Q sample and a K sample?+
The K, or known, sample has a documented, verified source used as the comparison standard, while the Q sample's relationship to that source is the question the analysis is meant to answer.
Why does contamination risk matter more for Q samples than K samples?+
Q samples are often collected from uncontrolled scene conditions with a single, non-repeatable opportunity to gather material, so any contamination directly threatens the conclusion, whereas K samples can usually be recollected under controlled conditions.
Related terms
- Certified Reference Material (CRM)
- A sample with one or more analyte concentrations established by an accredited body and traceable to a national metrology institute. NIST SRM...
- Known (K) Sample
- A sample with documented, verified provenance used as the reference in a comparison. The origin of a K sample is not in...
- Measurement Traceability
- The property of a measurement result whereby it can be related to a national or international measurement standard through an unbroken chain...
- Negative Control (Blank)
- A sample known to contain no target analyte, processed alongside casework samples. Confirms that background contamination is not producing false signals in...
- Positive Control
- A sample of known composition containing the target antigen at a concentration that should produce a defined signal. Run alongside case samples...