christian c. matchett, f-abc georgia bureau of investigation presented at
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Christian C. Matchett, F-ABCGeorgia Bureau of Investigation
presented at 2008 CLIC Technical Training Seminar
2007/2008 SWGDRUG Updates 2007/2008 SWGDRUG Updates Uncertainty DocumentUncertainty Document
Drug Enforcement AdministrationDrug Enforcement AdministrationOffice of Forensic SciencesOffice of Forensic Sciences
sponsored by the
National Institute of StandardsNational Institute of Standardsand Technologyand Technology
and the
2007/2008 SWGDRUG Updates 2007/2008 SWGDRUG Updates Uncertainty DocumentUncertainty Document
Why Address Uncertainty?Why Address Uncertainty?
Forensic community asking for guidance Accrediting bodies establishing measures of
assessing conformity with ISO Customer requirements Jurisdictional requirements
Transparency (nothing to hide) Potential Exculpatory Information
Core Committee Actions
Jan 2008 – Draft Uncertainty document approved and released for public comment
Posted on the website since February 2008 July 2008 – Comments were addressed and final
document adopted on July 22, 2008 The document should be posted on the website
by the end of September 2008
SWGDRUG ApproachSWGDRUG Approach
Tailor the recommendations to drug analysis and answer specific uncertainty questions
Ensure dialog on topic is not dictated to us by those outside of the seized drug community
Offer guidance and direction to laboratories and accrediting bodies
Aware that there is a wealth of information that already exists on Uncertainty
No intentions of repeating existing information
Purpose of DocumentPurpose of Document Provide General Guidance
Principles and themes conveyed, not step-by-step instructions
Raise Awareness and Put In Context Uncertainty is not doubt, it provides assurance
that results and conclusions are fit for purpose Determine Laboratory Responsibility
Consider customer requirements and address uncertainty through training, procedures and documentation
State Benefits Enhanced confidence through increased
understanding of results Provides Mechanism to express reliability of
results
Application of Application of UncertaintyUncertainty
Qualitative Quantitative
Purity Weights
Qualitative AnalysisQualitative Analysis
Individual methods have limitations and, consequently, uncertainty
Understanding limitations allows analysts to build an appropriate analytical scheme to correctly ID drugs or chemicals
It is expected that an appropriate analytical scheme will result in, effectively, no uncertainty in reported identifications
Relevant limitations should be documented and may need to be in report
Qualitative ExamplesQualitative Examples
Use Part III B Methods of Analysis/Drug Identification
IR and microcrystalline test positive for cocaine – effectively NO uncertainty
Limitations Marquis test positive for methamphetamine –
could be methamphetamine or other amphetamines
GC/MS test positive for ephedrine – could be ephedrine or pseudoephedrine
Quantitative AnalysisQuantitative Analysis
Uncertainty is defined as an estimate attached to a test result which characterizes the range of values within which the true value is asserted to lie
Precise calculations of measurement uncertainty is not always required
Seized Drug Numerical ResultsSeized Drug Numerical Results
Primary numerical values reported in the analysis of seized drugs are
Weight and Purity
Where a value is critical, an appropriate measurement uncertainty determination shall be applied
Weight close to a statutory threshold Purity of drug close to level which affects
sentencing
WeightWeight
Uncertainty of a reported value is dependant on the weighing process. Factors include:
Single item versus multiple items (# of weighing operations)
Tare function as separate weighing operation Extrapolation of population weight from limited
sampling of multiple items Aggregate weighings Incomplete recovery of material from packaging Balance selection (e.g., readability, capacity) Balance operation (e.g., sample placement,
environmental conditions)
PurityPurity
Sources of uncertainty for purity determination
Sampling plan (e.g., handling of multiple exhibits) Sample homogeneity
Analytical method Sample preparation (e.g., size, matrix effects,
solubility) Analytical technique Reference material (e.g., purity of standard) Equipment and instrumentation performance (e.g.,
glassware, pipetters, balances, chromatographs) Concentration of analyte Environmental conditions
Purity ApproachesPurity Approaches Analytical Error
Address both systematic and random error through method validation and quality assurance
Sampling Error The sample and sampling procedure are often
the greatest contributors to measurement uncertainty
Where appropriate, confidence levels (e.g., 95%, 99.7%) shall be selected based on considerations relevant to the analytical context
Record uncertainty information in validation documents and/or case records
Uncertainty BudgetUncertainty Budget
All sources of error are separately identified and tabulated
Assign values to each error source using Empirical data
Validation process, Historical performance data, Control chart data, proficiency tests
Published data Combination of empirical and published data
Can exclude insignificant sources Calculate combined and expanded uncertainty
using significant values for procedure
Non-Budget ApproachNon-Budget Approach
Example 1: Use of data from replicate analyses from a validated method with an appropriate sampling plan
Sources of uncertainty that are separately assessed in the budget method are collectively assessed by experimental measurements
Example 2: Use of two standard deviations (2σ) of the test method results from reproducibility data from the validation studies.
Provides an approximation of the measurement uncertainty for non-critical values
ReportingReporting
Uncertainty shall be documented but may not need to be reported Should be reported when
result impacts customer Even if not reported,
analysts shall be cognizant of the uncertainty associated with their results
When to Report Uncertainty?When to Report Uncertainty?
Jurisdictional Prevailing statutory requirement Relevant governing body (agency) requirements Customer requests Potential exculpatory value
Analytical Qualitative results where limitations are known (e.g.,
inability to differentiate isomers) Quantitative measurements where a value is critical
(e.g., weight or purity level close to statutory threshold)
Laboratory accreditation requirements
Qualitative Reporting ExamplesQualitative Reporting Examples
Contains Ephedrine or Pseudoephedrine Item tested: 5.2 grams net
Visual examination determined that the physical characteristics are consistent with a Schedule IV pharmaceutical preparation containing Diazepam. There was no apparent tampering of the dosage unit and no further tests are being conducted.
Contains cocaine (salt form not determined)
Quantitative Reporting ExamplesQuantitative Reporting Examples
Positive for cocaine in the sample tested Net weight of total sample: 5.23 grams ± 0.03 grams Quantitation: 54.7% ± 2.8%
Sample tested positive for cocaine Net weight: 5.23 grams Purity: 54.7% Confidence Range: ± 2.8%* Calculated net weight of drug: 2.8 grams of cocaine *Confidence range refers to a 95% confidence level
Training RecommendationsTraining Recommendations
Individuals responsible for determining, evaluating and documenting uncertainty shall be capable of demonstrating familiarity with foundational concepts and principles of estimating uncertainty
General metrology (terminology, symbols, etc.) Concepts of random and systematic error, accuracy,
precision, propagation of error, etc. Reporting conventions (sig. figs, truncating, rounding) Basic statistics (i.e., confidence interval, probability,
etc) All analysts shall be capable of explaining their
labs procedures for evaluating uncertainty of qualitative and quantitative analyses
Supplemental Documents to Supplemental Documents to FollowFollow
Uncertainty budget Control chart data applications Demonstration of balance control using
standard weight sets Summing weights from individual exhibits Expression of sampling uncertainty based on
confidence interval using multiple samplings
Core CommitteeCore Committee
• DEA – Nelson Santos DEA – Nelson Santos (Chair)(Chair)
• Secretariat – Scott Secretariat – Scott Oulton (non-voting)Oulton (non-voting)
• FBI - Eileen WaningerFBI - Eileen Waninger
• ASCLD – Garth ASCLD – Garth GlassburgGlassburg
• NIST - Susan BallouNIST - Susan Ballou
• ASTM and NEAFS- ASTM and NEAFS- Jack MarioJack Mario
• CAC & NWAFS - Jerry MassettiCAC & NWAFS - Jerry Massetti
• MAFS - Richard PaulasMAFS - Richard Paulas
• MAAFS - Linda JacksonMAAFS - Linda Jackson
• SAFS – Christian MatchettSAFS – Christian Matchett
• Toxicology – Dr. Robert PowersToxicology – Dr. Robert Powers
• Educator – Dr. Chris TindallEducator – Dr. Chris Tindall
• Educator – Dr. Suzanne BellEducator – Dr. Suzanne Bell
Core CommitteeCore Committee
Core CommitteeCore Committee
• Canada - Richard LaingCanada - Richard Laing
• Japan – Mr. Osamu Japan – Mr. Osamu OhtsuruOhtsuru
• United Kingdom - Dr. United Kingdom - Dr. Sylvia BurnsSylvia Burns
• Australia - Catherine Australia - Catherine QuinnQuinn
• Germany - Dr. Udo ZerellGermany - Dr. Udo Zerell
• ENFSI - Dr. Michael ENFSI - Dr. Michael BovensBovens
• UNODC - Dr. Iphigenia UNODC - Dr. Iphigenia NaidisNaidis
THANK YOU
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