Transcript 3PersonMixture#2

3 Person Example #2
Suspect Boxer Shorts
(The Ladies’ Man)
The Scenario
• Victim accused Subject of rape in store room
at a club
• But she waited 4 days to report it
• She could, however, describe the “Thomas the
Tank Engine” boxers of her assailant
• Investigation led to Suspect who indeed had
“Thomas the Tank Engine” boxers
The Scenario
• Accused said he didn’t do it
• He said he couldn’t have done it because he
had sex with a waitress in the store room of
the club that night
• The waitress said she had sex with him in the
store room at the club
The Egram
Enter question text...
1. Not interpretable by our
guidelines
2. Mixture of 3 people – no
stat
3. At least 3 people – no stat
4. Indeterminate mixture, CPI
5. We would exclude only
6. We have a way to deal with
it including a stat
My Interpretation
• (This is the part you REALLY must do before
looking at any references)
• Mixture
• Consistent with 3 persons
• 5 loci with nothing in the Danger Zone
• The remaining loci might have drop out
• Profile is interpretable and I can do a stat
The Interpretation
• Since you have 5 loci with everything above
stutter, why not just do a 5 locus CPI?
4.6.3. When using CPE/CPI (with no assumptions of number of contributors) to
calculate the probability that a randomly selected person would be
excluded/included as a contributor to the mixture, loci with alleles below the
stochastic threshold may not be used for statistical purposes to support an
inclusion. In these instances, the potential for allelic dropout raises the possibility of
contributors having genotypes not encompassed by the interpreted alleles.
4.6.3.1. Alleles below the stochastic threshold may be used for comparisons
and/or to establish the presence of a mixture or male DNA (e.g., Y allele at
amelogenin).
4.6.3.2. A restricted CPE/CPI may be applied to multiple major contributors
despite the presence of minor contributor(s) alleles below the stochastic
threshold; a description of how to calculate can be found in Section 5.3.5.
The Interpretation – CPI
• Cool! This one is easy
D8
THO1
D7
D13
D16
The Interpretation – CPI
• 4.6.3.2. A restricted CPE/CPI may be applied
• So if I have a “clear” major(s) I can also use
those loci!
• Maybe you could pull out a major here
D21
D19
D18
The Interpretation – CPI
• But…. Unfortunately all those “tall” peaks
match the owner of the boxers
– (I peeked – we were going to “interpret without
looking at the references”)
– (If we hadn’t at least looked at the
assumed/expected person/owner, we’d be in a
mess)
• But we still have those 5 loci >300
The Interpretation – CPI
• But do we really have 5 loci >300 for all alleles?
• SWGDAM - loci with alleles below the
stochastic threshold may not be used for
statistical purposes
• But there’s a huge hole in that
The Interpretation – CPI
• Look at THO1
• Are we positive the 9 is from a single
contributor?
• If not, it’s pretty much a given that:
– Someone is contributing <300
– Therefore, we have allele(s) <300
– Therefore, we can’t use that locus
THO1
The Interpretation – CPI
• Look at D13
• Pretty much certain that if we correct for
stutter, 13 <300
D13
• So much for that locus
• Now we’re down to 3 loci for CPI
The Interpretation – CPI
• D8 and D7 are no better
• Are you 100% certain all contributors
are >300?
• If there are 2 contributors to the 14 (D8)
and the 8 (D7) someone MUST be <300
because both are <600 rfu
• (Plus the 8 is in stutter position)
D8
D7
The Interpretation – CPI
• That leaves us with only D16 to consider
• There are only 2 alleles, and we already gave
up on other loci like this for 2 person mixtures
• And it’s even worse than it seems D16
The Interpretation – CPI
• D16 has “ghost” peaks
• So we “know” there are alleles missing here
even though all “detected” alleles are >300
• Bye, bye CPI
The Interpretation – Now what?
• RMP to the rescue!
• (With one “problem” at D16)
• But let’s look down in the baseline before we
decide how to move on
The Egram – Looking in the Weeds
The Interpretation – mod RMP
• Other than D16 I have no other concerns
about the baseline
• By that I mean I don’t see anything that if it
were “real” would change the interpretation
of “consistent with 3 contributors”
• Let’s look at some spots were it could possibly
be argued that’s not true, but I think it is
The Interpretation – mod RMP
• D3
10
48
• 5 Alleles called
• 3 more “blips”
• 5 + 3 = 8 so 4 people?
13
80
15.2
73
The Interpretation – mod RMP
• The 10 and 13
10
might be only
48
stutter
• The 15.2 probably
not
• Which would mean
“6” alleles, so still 3 people
13
80
15.2
73
The Interpretation – mod RMP
• Worst case scenario – 4 people for D3?
• Correct for stutter (50%) 2 “alleles” go away
• Consistent with 3 people!
The Interpretation – mod RMP
• So at D3, what happens if I have a reference to
compare that has a 15.2?
• As long as that person’s other allele is found in
the mixture there, they are still included
• Remember, I’m allowing for “Anys” so I expect
drop out is possible
• I wouldn’t exclude, but would make locus = 1
for that person
The Interpretation – mod RMP
• D2 is similar
• Could there be an
18, 20 or 26?
• 2 of those are in stutter positions
• We can test it again – Do we have more than
6 alleles?
The Interpretation – mod RMP
• Worst case scenario – 4 people for D2?
• Correct for stutter (50%) 2 “alleles” <20 rfu
• Consistent with 3 people?
The Interpretation – mod RMP
• Do I need to worry about “alleles” below 20?
• NO WAY!! So, consistent with 3 people
The Interpretation – mod RMP
• So that was a really LOOOOONNNNNG
discussion to say this:
• Just do a modified RMP
– It covers for all the “potential” drop out here,
since any drop out would still be consistent with 3
people
– But, we have to drop D16 from the calculation
– We “KNOW” there is drop out there
The Interpretation – mod RMP
•
•
•
•
•
The actual stat takes about 3 clicks
1. Open the sample into the Mix Interp Window
2. Operations>Mixture Frequency
3. 3 contributors
4. Open Frequency Report
• (OK, 4 clicks)
The Interpretation – mod RMP
D18
• Quick look at D18
• There are 3 Allele, Anys here
The Interpretation – mod RMP
• Quick look at D5
• There is 1 Allele, Any here
The Interpretation – mod RMP
• Quick look at FGA
• 6 Alleles and 3 People, so subtract homozygotes
The Interpretation – mod RMP
• The Final Stat
• 1 in 13,400
(1 in 462,000 if D16 kept)
Last Thought
• Remember D16?
• The “ghost” alleles?
• We dropped that locus for the stat
– Made it “1.0” mathematically
– It’s now a “neutral” locus
• The right LR model would cause D16 to be
supportive of Hd if POI were 12, 13 (the ghost
alleles)
Last Thought
• But, what form of the LR?
– Unrestrained combinatorial method?
– F or Q method?
– D method?
– Semi-continuous model?
– Continuous model?
• How many of us know what we mean when
we say “I need LR with drop out?”
Last Thought
• We are working hard to understand those LR
models
• We are moving towards a LR model that
incorporates Q and D
• We want to include our phr and p information
that we currently use for RMP
• This could then be considered a semicontinuous LR
Oops! We Forgot
• Is Victim included or excluded as a contributor
to the three person mixed DNA profile
recovered from the boxers of the Accused?
• She cannot be excluded
• What about the waitress????