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way of looking at it, would it be inaccurate to state it that
way?
A: It’s not inaccurate, no.
Q: All right. Then in response to my question, would the
likelihood that the semen from the DNA found in the
panties and the blood from Troy Brown, that it’s not the
same, would it be—the chances that they are not a match
would be .000033?
A: Yes. That’s the way the math comes out.
Q: All right.
THE COURT: Let’s make sure. It’s the same thing—it’s
the same math just expressed differently. Is that correct?
THE WITNESS: Yes. Exactly, your Honor.
THE COURT: Thank you.^37
As before, Romero initially resists the prosecution’s efforts to
turn an RMP into a source probability by stating a preference for
expressing the DNA statistic as a frequency rather than as a
probability. But Romero’s resistance misses the mark. As noted
above, it makes no mathematical difference whether a frequency
statistic is expressed as a frequency or as its equivalent
probability (decimal) value.^38 One in three million may be
described as .00000033 or as its percentage equivalent,
.000033%.
What Romero should have resisted was the prosecutor’s
attempt to convert the .000033% RMP statistic^39 into a posterior
(^37) Id. at 460–62.
(^38) Of course, although frequencies and their corresponding probabilities
are mathematically equivalent, people may respond differently to the form of
the presentation. Indeed, there is evidence that people respond differently to
frequencies and their mathematically equivalent probabilities in the context of
DNA statistics. See generally Jonathan J. Koehler & Laura Macchi, Thinking
About Low-Probability Events: An Exemplar-Cuing Theory, 15 PSYCHOL. SCI.
540 (2004) (finding that people were less persuaded by low probability DNA
evidence when it was presented in an exemplar-conducive way than when it
was not).
(^39) The prosecutor omits the “percent” on the .000033% RMP statistic.
Although surely unintentional, this omission inflates the RMP from one in
3,000,000 to one in 30,000. McDaniel Transcript, supra note 28, at 460–62.