Document ID: ./input/supremecourt_opinions/opinions/23pdf/22-899_97be.pdf
Page Number: 39

8 

SMITH v. ARIZONA 

ALITO, J., concurring in judgment 

that an expert’s opinion may be based on “facts or data in
the case that the expert has been made aware of or person-
ally observed.”  And “[u]nless the court orders otherwise,”
Rule 705 permits the expert to “state an opinion—and give
the reasons for it—without first testifying to the underlying
facts or data.” 

These facts or data need not be “admissible” in evidence, 
and they are not admitted for the truth of what they assert.
Fed. Rule Evid. 703.  Instead, these facts or data may, un-
der some circumstances, be disclosed to the jury for a lim-
ited purpose: to assist the jurors in judging the weight that 
should be given to the expert’s opinion.  Ibid.  However, this 
is not allowed unless the court determines that “their pro-
bative value in helping the jury evaluate the [expert’s] opin-
ion substantially outweighs their prejudicial effect.”  Ibid. 
And  to  prevent  the  jury  from  improperly  relying  on  basis
testimony  for  the  truth  of  the  matters  it  asserts,  a  judge 
must  instruct  the  jury  upon  request  to  consider  such  evi-
dence  only  to  assess  the  quality  of  the  expert’s  testimony 
(i.e., to determine whether an expert’s statements are reli-
able).  See Advisory Committee’s Notes on Fed. Rule Evid. 
703, 28 U. S. C. App.,  p. 393; Fed. Rule Evid. 105 (“If the
court admits evidence that is admissible . . . for a [limited]
purpose—but  not  . . .  for  another  purpose—the  court,  on
timely  request,  must  restrict  the  evidence  to  its  proper
scope and instruct the jury accordingly”).

This procedure is sensitive to the risk of jurors’ mistak-
enly treating an expert’s basis testimony as evidence of the
truth of the facts of data upon which the expert relied.  The 
Rules  provide  important  safeguards  against  this  danger, 
such as the stringent “probative value versus potential prej-
udice” test and the requirement that a limiting instruction 

—————— 
Arizona courts are free to interpret those rules as they see fit, and I do
not address the question whether the witness’s testimony was proper un-
der Arizona law.