Transfer and Persistence
Definition
The processes by which soil particles move from a source to an evidence item and remain there; relevant to forensic comparison design because both the amount transferred and the time since transfer affect the questioned sample's representativeness.
- Transfer
- Movement of soil particles onto an evidence item
- Persistence
- Retention of transferred material over time
- Relevance
- Both affect how representative a questioned sample is
- Context
- Forensic soil comparison casework
Common questions
Why does persistence matter as much as transfer in soil evidence?+
Even a large initial transfer can be lost to weathering, washing, or activity between the contact event and recovery, so what an analyst finally recovers reflects both processes, not the transfer event alone.
How does this affect interpreting a small amount of soil recovered from an item?+
A small recovered quantity does not necessarily mean minimal contact occurred. It may instead reflect a good initial transfer followed by poor persistence, so analysts avoid inferring contact duration from quantity alone.
Related terms
- Bayesian Inference
- A framework for updating probability estimates in the light of new evidence; in forensic science, used to combine the prior probability of...
- Control Sample
- A water sample collected from the suspected drowning environment at or shortly after the time of body recovery. Its diatom assemblage is...
- ENFSI ENG-FG1
- The European Network of Forensic Science Institutes' guidelines for forensic geological evidence, published in 2018 by the Expert Working Group on Forensic...
- FBI Soil Examination Unit
- The specialist unit at the FBI Laboratory in Quantico, Virginia, that has conducted forensic soil comparisons in federal criminal cases since the...
- Likelihood Ratio (LR)
- The ratio of two conditional probabilities: the probability of the observed evidence given the prosecution's hypothesis (same source), divided by the probability...
- Mahalanobis Distance
- A multivariate distance measure that expresses the separation between two observations in units of the population standard deviation, accounting for covariance; used...
- Murray-Tedrow Framework
- The tiered forensic-soil comparison protocol established by Raymond Murray and John Tedrow in their 1992 text 'Forensic Geology,' which organises soil examination...
- Principal Component Analysis (PCA)
- A multivariate statistical method used in fire debris research to reduce chromatographic data matrices to principal components that capture major variance. Used...
- Prosecution Proposition
- In the Bayesian evidence framework, the proposition that the questioned evidence item was in contact with or came from the crime scene;...
- Verbal LR Scale
- A standardised conversion table from numerical likelihood ratio values to phrases such as 'moderate support' or 'very strong support' for one of...
- Within-Scene Variability
- The natural compositional variation of soil properties over short distances within a single scene; must be characterised by multiple control samples before...