Okay. Dr. Cotton, you've given an opinion about usability of different types of--usefulness--excuse me--of different types of proficiency tests. Have you considered, in reaching your own opinions on this subject, the National Academy of Science recommendations with respect to measuring laboratory error rate through proficiency testing?
Well, I'm not asking you whether you agree with the National Academy of Science's recommendations, Dr. Cotton. What I'm asking you is whether or not these recommendations have been considered by you seriously before you arrived at your own opinions.
I read them, I thought about them and I have a different opinion than they do about the--whether or not what they're asking for is realistic and possible.
In reaching your own opinions on the subject of the utility of external blind proficiency testing, have you thus at least relied in part on what's contained in the NRC report, albeit you have disagreed or rejected, if you will, their recommendations?
Well, because I don't agree with it, I would say I haven't relied on it. I haven't used this in directing our laboratory to do the types of proficiency testing that we do.
Well, let me try and understand what you're saying, Dr. Cotton. Are you saying that it's your position that you only rely on those portions of the NRC report that you agree with?
What I'm say--I don't know how to say it more clearly. There are portions of this report that I agree with. There are a substantial number of portions of the report that I do not agree with, that I think either are not well considered or are simply wrong.
So is it fair for me to say, Dr. Cotton, that you have only relied on those portions of the NRC report in arriving at your own opinions that you personally agree with?
At the point that this report came out, I already had a substantial amount of experience at Cellmark and I had a much larger amount of experience working with DNA in general. I do not need this report to make my opinions.
I'm sorry, Dr. Cotton, but again, my question is, is it your position that you've only relied then for your own opinions on those portions of the NRC report that you agree with?
It's--what I'm saying is, I haven't relied on the report. If it happens that I agree with some things and disagree with some things, those things did not necessarily or have not necessarily played a role in my opinions about DNA typing and how it should be conducted.
Is it your professional and personal approach to the NRC report that if you don't agree with some of their recommendations, that you will not even take them into consideration in reaching your own conclusions?
Well, do you think, Dr. Cotton, that it is appropriate for scientists to give consideration to the opinions of other scientists with whom you disagree?
What do you mean, give consid--you can certainly think about them. I mean, the whole point, if somebody says, "I don't agree with you," is to think about it and formulate what your opinion is and see if it's the same or different and think about what somebody said. But if you have thought about it and you don't agree with it, then that's the situation.
And as to these various portions of the NRC report that you--that you disagree with, have you given serious thought to what the authors' recommendations are and why they've articulated them?
Dr. Cotton, are you familiar with any of the scien--any scientific literature concerning the use of external blind proficiency tests on laboratories doing PCR testing in clinical medicine?
Well, in your opinion, as an expert, Dr. Cotton, do you believe it would be important for someone in your laboratory to keep track of the rate of false positives for PCR testing in clinical medicine?
I don't--I don't actually have a really good answer for that. I'm not familiar with procedures in clinical medicine. We are familiar with procedures in forensic science. They very well may be different. Whether or not our quality assurance manager is familiar with clinical procedures, I can't tell you. I just don't know.
And some people, Dr. Cotton, say that a DNA test can only give you the right result or no result.
Have you ever heard that expression, Dr. Cotton, that a DNA test can only give you the right result or the wrong result?
I'm sorry. Can either give you the right result or no result. Have you ever heard that expression?
I mean, I'm hearing it now. I hear you saying it. Whether or not I've ever heard it before, I don't remember.
Well, now that you've heard it, Dr. Cotton, would you agree that that's not a correct statement?
And one of the reasons that it's much too black and white a statement, Dr. Cotton, is, I believe as you've already testified, a DNA test could give you a false positive?
It's possible that it could. It could also give you an inconclusive, could also give you a false negative. There's a lot of in between there.
And if the DNA test gives you a false positive, it means that you are getting a match between two samples that in fact come from different people; isn't that right?
And would you agree, Dr. Cotton, that if one laboratory made many errors in external blind proficiency testing and another laboratory made few, that the laboratory which made many more is more likely to make a mistake in a given case?
Given the generalization that you just stated, yes, I guess I would agree with that.
And you agree, Dr. Cotton, that interpretation of DNA typing results depends not only on the frequency of a DNA pattern, but on laboratory error rates as well?
Well, do you agree, Dr. Cotton, that the strength of a DNA evidence depends not only on the frequency of the pattern, but on laboratory error rates as well?
Well, Dr. Cotton, did you read that portion of the National Academy of Science report which discusses the role of laboratory error rates in assessing the weight of DNA evidence?
And have you considered seriously the points that the authors of the NRC report are making with regard to the importance of assessing the laboratory's error rate?
But you simply disagree with the National Academy of Science recommendations on this particular point; is that right?
Dr. Cotton, once again, are you saying that the reason you don't rely on this portion of the report is simply because you disagree with it?
Well, would you agree, Dr. Cotton, that the measure of a laboratory's error rate is a separate and independent issue from the measurement of the frequency of a DNA profile?
Well, would you agree, Dr. Cotton, that if someone was falsely implicated by an RFLP DNA test, it would much more likely be due to sample handling error or cross-contamination rather than due to coincidental match between people with the same RFLP profile?
Now, your laboratory has had at least a couple of instances where you had false matches due to sample handling error and cross-contamination; isn't that correct?
And using the definition of the four types of proficiency tests that I have given you in that diagram whose number escapes me--
Thank you--on 1153, in 1993, how many of your proficiency tests fall into the category of external blind proficiency tests?
Well, do you prepare a chart where you list the proficiency tests that you run in a given year? Do you have a chart like that?
And on that chart, do you actually identify which of the proficiency tests are internal versus which ones are external?
And on that chart, do you also differentiate between those that are blind and those that are open?
And would you agree by the way, Dr. Cotton, that at least for forensic cases, there's a difference between doing a proficiency test on a paternity sample with a mother and a child and a purported father than there is in forensic casework proficiency testing?
Okay. So my question is, Dr. Cotton, if you look at your memo, will you be able to tell us in 1993 how many blind external proficiency tests you did of a forensic nature?
Okay. And in 1992, Dr. Cotton, how many blind external proficiency tests utilizing forensic type samples did Cellmark participate in?
None. We have never done a blind external, received from an external agency proficiency tests because there is no external agency which provides those kinds of tests. So there is no way to get one.
So, Dr. Cotton, is to fair to say then, in the entire six years that your laboratory has been doing proficiency testing, there is not a single instance when you have ever been subjected to a blind external proficiency test?
Would you agree then, Dr. Cotton, that in the absence of being submitted to any blind external proficiency test, that you really have no scientific basis for estimating your laboratory's error rate?
Are you aware, Dr. Cotton, that the DNA laboratories that type bloods for bone marrow transplant registry routinely are subjected to blind external proficiency tests?
So would it be fair to say, Dr. Cotton, that the only types of tests that you have available for estimating your error rate as far as proficiency tests goes are either those tests where you were testing yourself or those tests where you knew you were being tested; is that correct?
Dr. Cotton, can you cite a single article in the field of laboratory quality assurance which permits a laboratory to assess its own error rate based on open and internal tests?
I'm about to move on to something new, your Honor. I don't know if you want to break now.
All right. Ladies and gentlemen, we are going to take our recess for the morning session. Please remember all of my admonitions to you; do not discuss the case amongst yourselves, don't form any opinions about the case, don't allow anybody to communicate with you, do not conduct any deliberations until the matter has been submitted to you. We'll stand in recess until 1:00 o'clock. All right. Dr. Cotton, you can step down.
I can tell you right now, blind external, there aren't any.
That's exactly right.
No, I can't.
I don't agree with their recommendations.
Yes. That's correct.