This is an interesting rule, which came up recently in a case:

An expert witness is permitted to use assistants in formulating his expert opinion, and normally they need not themselves testify; opposing party can depose them to make sure they performed their tasks competently, and expert witness can be asked at his deposition whether he supervised them carefully and whether his relying on their assistance was standard practice in his field. Fed.RulesEvid.Rule 703, 28 U.S.C.A.

Analysis becomes more complicated if the assistants aren’t merely gofers or data gatherers but exercise professional judgment that is beyond the expert’s ken.
Dura Automotive Systems of Indiana, Inc. v. CTS Corp.
United States Court of Appeals, Seventh Circuit.April 4, 2002285 F.3d 60952

In my cases, many times I use an administrative assistant to do typing, extensive number crunching, pivot table setup, and other laborious excel tasks. My understanding from the above is that if I supervise the work than I can take ownership of it, as if I did the work. I, like larger forensic and expert witness firms, don’t have the expertise or time to develop complicated graphics. It wouldn’t make sense to pay me $250/hr to develop a table. I hand-write the table, give it to Fedex/Kinko’s or my staff, who will create a large version of a chart, a pictorial or other ‘end-product’.

In a recent case there was an issue when I asked a party’s relative to create a graph-it wasn’t admitted into evidence in a state case, because of an independence issue. Even though I created the ideas in the chart, it was seen as biased or susceptible to such. Fortunately the related testimony was accepted, and many other charts were as well.

In the future I will continue to pay attention to this area so that I can strike the correct balance between being economical for the client, and including professional oversight so that if a secretary or other person helps with an administrative project the work will continue to be admitted.