📄 Motion: DNA mixture statistics admissibility — Friday, June 16, 1995
Address:
C:\DEPT103\CRIMINAL\1995\JUN\16\MOTION-DNA-MIXTURE-STATISTICS-.DOC
TRIAL
▲ Day 97 of 167

Motion: DNA mixture statistics admissibility

Date: Friday, June 16, 1995 • Utterances: 51
Defense attorney Thompson raised three issues about the prosecution's plan to present likelihood ratio statistics for DNA mixture evidence through Dr. Bruce Weir: whether such novel statistics should be allowed at all, whether a 402 admissibility hearing was required, and whether the defense needed more time to prepare. Judge Ito signaled strong skepticism about likelihood ratios, noting no appellate precedent exists for their use in criminal prosecutions, and directed both sides to schedule a 402 hearing.
1 THE COURT:

All right. Mr. Thompson, do you have a matter?

2 MR. THOMPSON:

Yes, your Honor.

3 THE COURT:

What is that?

4 MR. THOMPSON:

Good morning. We need to briefly revisit the issue of the statistics to be presented in connection with the DNA mixtures, and earlier this week the Court directed the Prosecution to let us know what their intentions were with regard to these statistics and particularly whether they were intending to present likelihood ratio statistics which are a novel form of statistical presentation on this matter. Yesterday--late yesterday Mr. Clarke let us know that the Prosecution does indeed intend to present likelihood ratio statistics, that they are intending to present them next Tuesday through their witness, Dr. Bruce Weir, and that the Defense will not be given a final copy of Dr. Bruce Weir's report until late next Monday. This revelation raises three issues that I would like to raise and discuss with the Court at this--at this point. The first issue is whether the Prosecution should be allowed to present novel unprecedented form of statistical evidence on mixtures at this juncture in the case, given the posture of the evidence and given the Court's previous rulings on this subject. The second issue is the need for a 402 hearing in the event that the Court entertains letting the Prosecution establish the admissibility of this new kind of statistical evidence. We feel very strongly that a 402 hearing is required and we need to discuss briefly the scope and parameters of such a hearing. The third issue is the need by the Defense for more time. The fact that we are getting the final report the night--essentially the night before the Prosecution intends to present this new evidence just simply does not give us enough time to prepare. We have received a preliminary report from Dr. Weir, but it does not include data or calculations; it makes citations. It says that it is a calculational approach based on scientific articles which are not cited. They don't give us the citations to the article. We have been unable to find them. And we will need--regardless of whether have we have a 402 hearing or not, we will need additional time to prepare and we would like a week. And so those are the issues. I can take them in any order that you please.

5 THE COURT:

Do you need to say more about them?

6 MR. THOMPSON:

Well, I am prepared now to give you an argument on the first point as to why we feel that the Prosecution should simply be precluded from presenting this kind of evidence. We think the--we have no objection, your Honor, to the presentation of aggregate statistics in the form recommended by the national research council, which we have discussed earlier in this case. It is a very simple form of statistical calculations which simply adds up the frequency of all the genotypes that would match with the mixture. We have no objections to at all. We think it is simple and easy to understand. We have a series of very strong objections which we stated in our papers and in previous arguments. But basically our position is that the effort to present a novel form of statistical analysis on the mixtures at this point should be precluded in light of the Court's previous rulings and the posture of the evidence in this case. When the Court ruled in may that the Prosecution must present statistics on these mixtures, I think everybody contemplated that they would be frequency statistics which were the same sorts of statistics present on all the other DNA evidence.

7 THE COURT:

Well, Mr. Thompson, let me perhaps give you insight into the Court's thinking on this. And are you aware of any appellate case that addresses the admissibility of likelihood ratios in a criminal Prosecution case anywhere in the United States?

8 MR. THOMPSON:

None at all.

9 THE COURT:

The only three likelihood ratio cases, reported cases nationwide, deal with likelihood ratios in paternity cases, which is obviously not the situation we are dealing with here.

10 MR. THOMPSON:

I agree completely.

11 THE COURT:

Mixtures, et cetera, et cetera.

12 MR. THOMPSON:

Yes. If I understand you correctly, you are saying you view this as an unprecedented matter. We do as well.

13 THE COURT:

I think it is from beyond novel to being unique.

KEY QUOTE
14 MR. THOMPSON:

Yes.

15 THE COURT:

All right.

16 MR. THOMPSON:

All right. So if I--

17 THE COURT:

And I made a ruling back in June that I think was pretty clear.

18 MR. THOMPSON:

All right. So it sounds like your thinking coincides with ours, that the Prosecution should simply be precluded from presenting statistics in the likelihood ratio form at this juncture.

19 THE COURT:

Well, I think at the very minimum, if they insist on proceeding with that, I think we need a 402 hearing out of the presence of the jury.

20 MR. THOMPSON:

All right. Well, let's proceed to that. In the event we have such a hearing, the Defense would intend to call one and possibly two witnesses in order to explain why we feel statistics presented in that form are inappropriate as a scientific and statistical matter on the one hand, and on the other hand, why this form of statistical presentation is likely to be grossly misleading to the jury. I estimate we would need approximately two hours of expert testimony to establish those points.

21 THE COURT:

All right.

22 MR. THOMPSON:

But we--in order to prepare for such a hearing we need more time than overnight after getting the final report which shows what the Prosecution is going to present, so we would like to put it off for a week, if possible.

23 THE COURT:

All right. Thank you, Mr. Thompson. Miss Clark, good morning.

24 MS. CLARK:

Thank you, your Honor. We find ourselves in this unique posture because the Defense has insisted on doing something that is scientifically unsound, and that is to apply frequency ratios to a mixture. That is not done in scientific circles. It is not an accepted scientific practice to assign numbers to bloodstain mixtures.

25 THE COURT:

Isn't that what the NRC report recommends at page 69?

26 MS. CLARK:

No, not as to mixtures it doesn't. Yes, it says that we should assign frequencies to type results, but I don't believe there is any place I have ever seen in the NRC report where it specifically says that mixtures should be reported with numbers. And the problem is, if you want to do something scientifically unsound as to put a number to a mixture stain, then the most scientifically acceptable or accurate method of doing so is to assign it a likelihood ratio. We understand the Court's concern, because it is something unusual. The circumstances are themselves.

27 THE COURT:

You agree it is unique?

28 MS. CLARK:

I do, absolutely.

29 THE COURT:

All right.

30 MS. CLARK:

That is why we are more than happy to present Dr. Weir's testimony to the Court. I think it is entirely appropriate. There is no question about that.

31 THE COURT:

Well, counsel, what I indicated to Mr. Thompson is that if you feel that that is the way it needs to be presented, then I think what we are looking at is a 402 hearing.

32 MS. CLARK:

And I--the People aren't arguing with that. The question is the timing, your Honor.

33 THE COURT:

Okay. Well, when would your expert be available? When is Dr. Weir available?

34 (Discussion held off the record between the Deputy District Attorneys.)
35 MS. CLARK:

Wednesday. We had anticipated presenting his testimony on Wednesday and so he has arranged to be here on that date. And I--we all don't want to take the jury's time up.

36 THE COURT:

I know, but we may have to, but seeing as how we avoided a eight-week--six to eight-week Kelly-Frye hearing, you know, maybe a day or two out, we can take them to Disneyland or something. I'm sure we can find something for them to do.

37 MS. CLARK:

Yeah.

38 THE COURT:

All right. But my other concern, though, is I think that since this is a novel issue, because the Court's research indicates that likelihood ratios have not been presented in any criminal Prosecution that I have been able to find, at least at the appellate level. There may be some on a trial court level, but I'm not aware of any at this point, but I am willing to look and see.

39 MS. CLARK:

Okay. Yeah. We will present to the Court everything that we gather on this and I'm sure Dr. Weir is aware of where that has been presented before.

40 THE COURT:

The issue is also timing because I think the Defense is entitled to see Dr. Weir's report and know what literature he is referring to and then have reasonable time to prepare.

41 MS. CLARK:

Of course.

42 THE COURT:

So that is something that--I would ask that Mr. Harmon and Mr. Thompson, while we are continuing with the glove evidence, confer as to availability of their witnesses knowing that if the Prosecution wants to present likelihood ratios we will probably need a 402 hearing.

43 MS. CLARK:

Okay. Umm--

44 THE COURT:

And it sounds to me like half a day to a day because we are talking about statistical methodology is what we are talking about.

45 MS. CLARK:

Right. That does sound right, your Honor.

46 THE COURT:

Okay.

47 MS. CLARK:

Then question I have is if we turn over the report, and I understand we can do so Monday afternoon, if we present the testimony on Wednesday for the 402, wouldn't that be sufficient time for the Defense to read the reports and be ready to cross-examine Dr. Weir and present their testimony?

48 THE COURT:

Could be.

49 MS. CLARK:

Okay. Okay. I will just wait and see.

50 THE COURT:

All right. Why don't--let me have Mr. Thompson and Mr. Harmon consult since they are both here today and just find out schedules and who is available what days and then we will take from it there.

51 MS. CLARK:

Okay.

Temperature

tense

Key Quotes (4)

Lance A. Ito
I think it is from beyond novel to being unique.
Ito signals he views likelihood ratio statistics as unprecedented in criminal cases, telegraphing that he will require a formal admissibility hearing and may exclude the evidence.
Marcia Clark
We find ourselves in this unique posture because the Defense has insisted on doing something that is scientifically unsound, and that is to apply frequency ratios to a mixture. That is not done in scientific circles.
Clark reframes the dispute — arguing the defense's preferred statistic (aggregate frequencies) is itself scientifically improper for mixtures, justifying the prosecution's use of likelihood ratios as the more defensible approach.
Lance A. Ito
Seeing as how we avoided a eight-week--six to eight-week Kelly-Frye hearing, you know, maybe a day or two out, we can take them to Disneyland or something.
Ito uses humor to defuse tension while acknowledging the jury will need to be occupied during a 402 hearing, referencing the earlier Kelly-Frye DNA admissibility battle that was avoided.
Mr. Thompson
The fact that we are getting the final report the night--essentially the night before the Prosecution intends to present this new evidence just simply does not give us enough time to prepare.
Captures the defense's procedural fairness argument — the prosecution's late disclosure of Weir's methodology deprived them of meaningful preparation time.

Evidence (2)

Informal
Dr. Bruce Weir's preliminary report on likelihood ratio statistics for DNA mixtures — described as lacking data, calculations, and article citations
discussed, challenged on disclosure timing
Informal
NRC (National Research Council) report, page 69 — cited by both sides regarding statistical methodology for DNA mixtures
disputed — Ito cited it as recommending frequency statistics; Clark argued it does not specifically address mixture stains

Notable Exchanges (3)

Lance A. ItoMr. Thompson
Ito interrupted Thompson's argument to reveal the court's own research finding no appellate precedent for likelihood ratios in criminal cases, effectively agreeing with the defense's position before Thompson could fully argue it.
strategic
Lance A. ItoMarcia Clark
Clark argued aggregate frequency statistics are scientifically unsound for mixtures; Ito pushed back by citing NRC page 69, forcing Clark to narrow her claim to mixture-specific statistics.
probing
Marcia ClarkMr. Thompson
Ito directed Harmon and Thompson to confer on scheduling a 402 hearing, with Clark proposing report delivery Monday and testimony Wednesday as sufficient turnaround for the defense.
procedural

Light Moments (1)

Lance A. Ito
Ito joked that since a six-to-eight week Kelly-Frye hearing was avoided earlier, the jury could be sent to Disneyland for a day or two while the 402 hearing proceeds.

Witness Demeanor

(Discussion held off the record between the Deputy District Attorneys.)

Objections

None recorded
Proceeding 6427 • 51 utterances
Criminal Trial
Department 103
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📂 JUN 16, 1995 📄 Motion: DNA mixture statistics
JUN 16, 1995 KRT DvH TD