Positivity Threshold
Definition
The minimum number of frustules per gram of tissue or per slide that a laboratory uses to declare a result positive. No universal standard exists; threshold proposals in the literature range widely, and different thresholds applied to the same case can produce opposite conclusions.
Related terms
- Background Contamination
- Diatom frustules introduced into a sample from sources other than the victim's own body: tap water, laboratory air, unclean glassware, reagents, and...
- Diatom Density
- The number of frustules per unit volume of water in the drowning environment. Low-density environments (pools, tap water, diatom-poor rivers) cannot deliver...
- False Negative
- A negative result from a preparation in which ante-mortem drowning actually did occur. Causes include low diatom density in the drowning water,...
- False Positive
- A test result that indicates the presence of a target analyte when it is absent. In forensic serology this may mean incorrectly...
- Standardisation
- The production of a validated, peer-reviewed protocol that specifies every variable in the test: acid type and concentration, digestion time and temperature,...
Explained in
- Limitations and Controversies of the Diatom TestThe minimum number of frustules per gram of tissue or per slide that a laboratory uses to declare a result positive. No universal standard exists; threshold pr...