I mentioned here my contention that the only way to cross-examine an expert witness about his conclusions is to know at least as much, if not more about the narrow subject of his testimony that hurts you than he does. It’s my position that, while I will probably never know as much about pediatrics than the State’s expert, I can know more about hymenal notching than him or her. (I use pediatrics and hymenal notching as an example because pediatrician testimony is often used by the State in cases involving false allegations of child sexual abuse. Courts will, for reasons that escape me, allow these experts to testify that the medical evidence is “not inconsistent with” the allegations.)
Where do we begin our own scientific or other technical education? With a narrowing of the inquiry. The process of deciding what premises we will challenge can be shortcut considerably if we can talk with the State’s expert beforehand and he will discuss his findings with us. If the case is adequately funded, we may have an expert of our own to consult with; she might be able to divine the State’s expert’s assumptions.
Otherwise, the expert’s premises will sometimes be laid out for us, or at least deducible from the subject matter of the expert’s testimony. For example, we might note that the expert observed several conditions (A, B, C) and concluded from these conditions that X happened. We can set down several premises that this conclusion might depend on:
That A shows that X happened;
That B shows that X happened; or
That C shows that X happened.
These are some of the things that we want to investigate, but not all. Even if we could show that none of these premises were true, we would have to investigate four other possible premises:
That A and B show that X happened;
That A and C show that X happened;
That B and C show that X happened; and
That A, B, and C together show that X happened.
A and B together might have much greater significance than either condition alone.
So now we have a list of the premises that we want to test — seven in this example. What do we do next?
Tune in tomorrow to find out.
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