Bandera de Estados Unidos

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Communication Skills, Report Writing, and Courtroom Testimony for Forensic Analysts

Mixed Source

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Reporting Guidelines - Mixed Samples

ResultsReporting

Major or Inferred component can be determined, and matches a known sample (and is probative)

Random Match Probability Statement (generally only given on probative samples)

Major/Inferred Component

  • A mixed DNA profile was obtained from ___.  The major (or inferred) component of this mixed DNA profile matches ___.  The approximate incidence of this major (or inferred) component of this profile is 1 in __ Caucasians, 1 in ___ Black, and 1 in ___ Southwestern Hispanics (or use appropriate population groups).
  • A mixed DNA profile from at least ___ sources was obtained from ___.  Assuming only ___ donors, the major (or inferred) component of this mixed DNA profile matches ___.  The approximate incidence of this major (or inferred) component of this profile is 1 in __ Caucasians, 1 in ___ Black, and 1 in ___ Southwestern Hispanics (or use appropriate population groups).
  • A mixture was observed on ___ that is consistent with originating from two or      more individuals.  A major DNA component can be determined.

Minor (or other) Component

  • ___ cannot be excluded as the minor (or other) component of the mixed DNA profile
  • No conclusions can be drawn as to the source(s) of the weaker alleles (or other contributors).
  • No conclusions were drawn as to the source(s) of the weaker alleles (or other contributors).

Major, minor, or inferred component can be determined that does not match any known samples (and is probative)

Note: Statement regarding NDIS will only be included for samples meeting the standards for inclusion/uploading.

  • A mixed DNA profile was obtained from ___.  The major (or inferred) component of this mixed DNA profile is from an unidentified source. This major (or inferred) component will be searched against the DNA profiles in the National DNA Index System (NDIS) and any matches will be reported.
  • A mixed DNA profile from at least ___ sources was obtained from ___.  Assuming only ___ donors, the major (or inferred) component of this mixed DNA profile is from an unidentified source. This major (or inferred) component will be searched against the DNA profiles in the National DNA Index System (NDIS) and any matches will be reported.
  • A mixture was observed on ___ that is consistent with originating from two or      more individuals. A major DNA component can be determined.

Minor (or other) Component

  • ___ cannot be excluded as the minor (or other) component of the mixed DNA profile.
  • No conclusions can be drawn as to the source(s) of the weaker alleles (or other contributors).
  • No conclusions were drawn as to the source(s) of the weaker alleles (or other contributors).

Major, minor, or inferred component can NOT be determined

-OR-

The minor component is of probative value

Likelihood Ratio (note that this calculation can be changed to accommodate mixtures of more than two persons)

Combined Probability of Inclusion

Combined Probability of Exclusion

Likelihood ratio example (assuming 2 donors)

  • A mixed DNA profile from at least two sources was obtained from ___.  Assuming only two sources, this profile is consistent with the combined DNA profiles from source 1 and source 2.

I have therefore considered two possibilities:

  • The DNA is a mixture of source 1 and source 2.
  • The DNA is a mixture of source 1 and an unidentified source.
  • The mixed DNA profile from ___ in the Caucasian population is x times more likely to be obtained if it is a mixture of source 1 and source 2 than if it is a mixture of source 1 and an unidentified source.  For the Black population the number is x and for the Southwestern Hispanic population it is x. (or use appropriate population groups).

Combined probability of inclusion example

  • A mixture was observed on  __ that is consistent with originating from two or       more individuals. ___ cannot be excluded as a possible donor to the DNA profile obtained.  The Combined Probability of Inclusion (CPI), or the expected frequency of individuals who could contribute to a portion of the mixture, is approximately 1 in ___ for Caucasians, 1 in ___ for Black, and 1 in ___ for Hispanics. (or use appropriate population groups).

Combined probability of exclusion example

  • A mixture was observed on __ that is consistent with originating             from two or       more individuals. ___ cannot be excluded as a possible donor to the DNA profile obtained.  The combined probability of exclusion (CPE) calculated for this mixture estimates that over 99.99% of individuals in the Caucasian, Black, and Southeast Hispanic populations can be excluded as contributors. (or use appropriate population groups).

Major, minor, or inferred component can NOT be determined

-OR-

The minor component is of probative value

One of the contributors is unidentified.

Likelihood ratio example (assuming 2 donors)

  • A mixed DNA profile from at least two sources was obtained from ___.  Assuming only two sources, this profile is consistent with the combined DNA profiles from source 1 and source 2.
  • I have therefore considered two possibilities
  • The DNA is a mixture of source 1 and an unidentified source.
  • The DNA is a mixture of two unidentified sources.
  • The mixed DNA profile from ___ in the Caucasian population is x times more likely to be obtained if it is a mixture of source 1 and an unidentified source than if it is a mixture of two unidentified sources.  For the Black population the number is x and for the Southwestern Hispanic population it is x. (or use appropriate population groups).

Combined probability of inclusion example

  • A mixture was observed on  __ that is consistent with originating from two or more individuals. ___ cannot be excluded as a possible donor to the DNA profile obtained.  The Combined Probability of Inclusion (CPI), or the expected frequency of individuals who could contribute to a portion of the mixture, is approximately 1 in ___ for Caucasians, 1 in ___ for Black, and 1 in ___ for Hispanics. (or use appropriate population groups).

Combined probability of exclusion example

  • A mixture was observed on __ that is consistent with originating from two or more individuals. ___ cannot be excluded as a possible donor to the DNA profile obtained.  The combined probability of exclusion (CPE) calculated for this mixture estimates that over 99.99% of individuals in the Caucasian, Black, and Southeast Hispanic populations can be excluded as contributors. (or use appropriate population groups).
Complex Mixture (exhibiting probable allelic dropout, degradation, and/or preferential amplification)—The analyst may not be able to make conclusions as to the individuals that can be potentially included/excluded.
  • Mixed DNA results were obtained from ___.  Due to the nature of this mixture, no conclusions were drawn.
  • Partial DNA results were obtained from ___.  Due to the nature of this mixture, no conclusions were drawn.

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