FOR PUBLICATION
  UNITED STATES COURT OF APPEALS
       FOR THE NINTH CIRCUIT

UNITED STATES OF AMERICA,                  
                 Plaintiff-Appellee,
                v.
87.98 ACRES OF LAND MORE OR                       No. 06-15410
LESS IN THE COUNTY OF MERCED;                       D.C. No.
CALIFORNIA DEPARTMENT OF FISH &                CV-03-06064-AWI/
GAME; KAREN ADAMS,                                    LJO
                       Defendants,                  OPINION
               and
DONN RAYMOND CAMPION,
             Defendant-Appellant.
                                           
         Appeal from the United States District Court
            for the Eastern District of California
         Anthony W. Ishii, District Judge, Presiding

                   Argued and Submitted
        February 14, 2008—San Francisco, California

                        Filed June 24, 2008

   Before: William C. Canby, Jr. and Milan D. Smith, Jr.,
   Circuit Judges, and Stephen G. Larson,* District Judge.

                     Opinion by Judge Canby




  *The Honorable Stephen G. Larson, United States District Judge for the
Central District of California, sitting by designation.

                                 7277
7280              UNITED STATES v. CAMPION
                        COUNSEL

John Derrick, Santa Barbara, California, for the defendant-
appellant.

Leslie B. Bellas (brief), Mary Gabrielle Sprague (argument),
United States Department of Justice, Environment & Natural
Resources Division, Washington, D.C., for the plaintiff-
appellee.


                         OPINION

CANBY, Circuit Judge:

   In this case, we review a district judge’s discretion to
exclude expert testimony regarding electromagnetic fields
(“EMFs”) in a condemnation action. The United States con-
demned an easement on land belonging to Donn Campion for
the construction of power transmission lines. At trial, both
sides offered expert testimony regarding diminution of value
of the remaining land resulting from the power lines within
the easement. While some of this testimony was allowed, the
judge refused to let Campion’s expert, an environmental plan-
ner, testify about specific EMF levels on the land and the
types of questions developers typically ask her about EMFs.
A jury found that Campion was entitled to just compensation
in the amount of $2,023,715. The district court entered judg-
ment, and Campion appeals the exclusion of expert testimony.
We affirm.

               FACTUAL BACKGROUND

   Campion owns 3,220 acres of land in Merced County, Cali-
fornia. Acting on behalf of the Department of Energy and the
Western Area Power Administration, the United States filed
an eminent domain action to acquire a right of way easement
                    UNITED STATES v. CAMPION                  7281
across the land for a 500kV power transmission line called the
Path 15 line. The Path 15 line was constructed and is now
operational. It rests on a 200-foot-wide easement running for
approximately three miles across Campion’s land and cover-
ing 87.98 acres. The line is supported by 13 steel towers rang-
ing in height from 130 to 190 feet, and branching out 40 feet
on two sides.

  Like other live power lines and electrical devices, the Path
15 line generates EMFs that radiate out from the line. There
was testimony that the Path 15 line sometimes emits crackling
and buzzing sounds. While there is no scientific evidence that
EMFs from power lines like the Path 15 line cause adverse
health effects in nearby residents, there is a generally
acknowledged public perception that EMFs cause health
problems.

   At the time that the easement was taken, Campion’s land
was undeveloped and used for agricultural purposes. The land
had been zoned for agricultural use, with a minimum parcel
size of 160 acres. The government’s expert appraiser, Correia,
testified that, at the time of the taking, the highest and best use
of the property was for agricultural purposes. On that basis,
he valued Campion’s entire property at $3.075 million. He
further testified that the taking caused no diminution of the
value of the land outside the easement. Accordingly, he testi-
fied that the government should pay $76,518 as just compen-
sation for the taking of the easement, and only the easement.

   Before the taking occurred, however, Campion had begun
creating plans to develop part of the land for residential use,
a golf course, a community village center, and public facili-
ties. His expert appraiser, Gimmy, testified that the highest
and best use of the land at the time of the taking was for such
a residential development. On this assumption, Gimmy put
the pre-taking value of the land at $19.320 million. Gimmy
also concluded that the power transmission lines diminished
the value of the land outside of the easement. Barred from tes-
7282                  UNITED STATES v. CAMPION
tifying that the mere existence of EMFs on Campion’s land
reduced the land’s value, Gimmy cited public perceptions of
power lines, environmental issues limiting development in
other areas of the property, aesthetic issues, and the practicali-
ties of developing around power lines. He concluded that,
after the taking, the property would have no residential poten-
tial. Rather, cattle grazing would be the highest and best use
of the entire property after the taking. He concluded that the
value of the property after the taking was $3.22 million, war-
ranting a $16.1 million compensation award. Of this amount,
only $1.415 million was attributable to the easement itself as
opposed to severance damages.

   Gimmy’s opinion was influenced by the report of another
of Campion’s experts, Cindy Sage, an environmental planner
with extensive experience advising developers regarding the
impact of EMFs from power transmission lines on the use and
development of property. Sage proposed to testify to the fol-
lowing: (1) public perceptions of the effects of EMFs among
residential homeowners and home buyers, (2) the extent and
level of EMFs from the Path 15 line that reach beyond the
easement into the rest of Campion’s property, and (3) the
types of studies concerning EMFs for which developers rou-
tinely engage her. Of these subjects, the trial judge permitted
Sage to testify only to public perceptions. In this appeal, Cam-
pion challenges the exclusion of the latter two subjects.

                           DISCUSSION

   Because Sage was not an expert appraiser and there had
been no showing that her EMF measurements were reliable,
the district judge excluded her testimony except to the extent
that Gimmy relied upon it in reaching his conclusion. The dis-
trict court also ruled—and Campion does not dispute on
appeal—that there could be no evidence at trial that EMFs
cause actual health problems in nearby residents.1 On this
  1
   This ruling accords with widespread authority holding that such evi-
dence is not scientifically reliable. See, e.g., San Diego Gas & Elec. Co.
                     UNITED STATES v. CAMPION                      7283
basis, Gimmy was barred from testifying that the mere exis-
tence of EMFs on Campion’s land reduced the land’s value.
Therefore, Sage was allowed to testify only regarding public
perceptions of EMFs.

   The judge excluded Sage’s testimony regarding EMF levels
as prejudicial, reasoning that testimony about specific EMF
levels on Campion’s land (including a map that outlined a
“zone of impairment”) might tend to prejudice a jury inclined
to believe that EMFs do, in fact, cause health problems in
nearby residents. The judge excluded Sage’s testimony
regarding the EMF studies she would perform for developers
for similar reasons. Because the trial judge acted within his
discretion in excluding the evidence, we affirm.

I.   Standard of Review

   A trial court’s decision to exclude expert testimony as irrel-
evant, see Fed. R. Evid. 402, or unfairly prejudicial, see Fed.
R. Evid. 403, in a Fifth Amendment action for just compensa-
tion is reviewed for abuse of discretion. See United States v.
33.5 Acres of Land, 

, 1400 (9th Cir. 1986);
United States v. Ravel, 

, 726 (9th Cir. 1991).
When it is not clear whether relevance or unfair prejudice
formed the basis for the district judge’s ruling, if the proffered
testimony could be excluded under either rule, we must
affirm. United States v. Morales, 

, 1035 (9th
Cir. 1997).

II. Severance Damages in Power Line Condemnation
Proceedings

  [1] When the government condemns part of a parcel from
an owner, it is liable not only for the part taken but also for

v. Daley, 

, 150-53 (Cal. Ct. App. 1988), disapproved of
on other grounds by L.A. County M.T.A. v. Cont’l Dev. Corp., 

(Cal. 1997).
7284              UNITED STATES v. CAMPION
the diminution of value in the remainder resulting from the
severance. See United States v. 4.0 Acres of Land, 

, 1139 (9th Cir. 1999). The excluded evidence bears on
the effect of the power lines on market value outside of the
boundaries of the easement. Campion, as the landowner in
this case, bears the burden of proving his entitlement to these
“severance damages.” United States ex rel. Tenn. Valley Auth.
v. Powelson, 

, 273 (1943). As the proponent of
Sage’s expert testimony, Campion also has the burden to
establish its admissibility. Lust v. Merrell Dow Pharm., Inc.,

, 598 (9th Cir. 1996).

   [2] Wholly apart from evidence of actual health risks, evi-
dence of public perceptions of health risks—even irrational
public perceptions—may properly establish an impact on
market value. “[I]f fear of a hazard would affect the price a
knowledgeable and prudent buyer would pay to a similarly
well-informed seller, diminution in value caused by the fear
may be recoverable as part of just compensation.” United
States v. 760.807 Acres of Land, 

, 1447 (9th
Cir. 1984) (citations omitted). A party may therefore intro-
duce evidence to show how public fears of EMFs, even if they
are unreasonable, adversely affect value. See id.; San Diego
Gas & Elec. 

(gathering cases).
Thus, the admissibility of Campion’s EMF evidence hinges
on this latter factor—the extent to which EMFs bear on public
perceptions in the marketplace.

III.   Evidence of EMF Levels and Locations

   In the district court, Campion’s offer of proof showed that
Sage was willing to give expert testimony regarding the levels
and locations of EMFs resulting from the construction and
operation of the power line. Specifically, Sage proposed to
testify that certain levels of EMFs extended beyond the physi-
cal boundaries of the easement into the remainder of Campi-
on’s land. Both parties seem to agree that the Path 15 lines
would generate EMFs on Campion’s land beyond the area of
                       UNITED STATES v. CAMPION                        7285
the easement, and two witnesses testified to that effect.2 Cam-
pion challenges only the exclusion of more detailed informa-
tion about the specific levels of EMFs on the land.

   Federal Rule of Evidence 702 provides that a court may
admit testimony from a qualified expert if it will help the trier
of fact understand the evidence or determine a fact in issue.
Such evidence must still be relevant; “[e]xpert testimony
which does not relate to any issue in the case is not relevant
and, ergo, non-helpful.” Daubert v. Merrell Dow Pharm.,
Inc., 

, 591 (1993) (internal quotation marks and
citation omitted). Such testimony must be shown to be either
scientifically reliable, 

or otherwise reasonably
reliable. Kumho Tire Co. v. Carmichael, 

, 158
(1999). Campion contends that there is no dispute as to the
reliability of Sage’s measurements, despite comments by the
district judge suggesting that the evidence could not be admit-
ted as freestanding expert testimony because there had been
no reliability showing under Daubert or Kumho Tire. Even if
Sage’s testimony was not demonstrated to be reliable, it might
still be admissible under Federal Rule of Evidence 703, which
provides that otherwise inadmissible evidence may yet be
admissible as the basis for an expert’s opinion if its “probative
value in assisting the jury to evaluate the expert’s opinion
substantially outweighs [its] prejudicial effect.” If the evi-
dence is admissible of its own accord—and not merely as
background for other expert testimony—then it is subject to
the standard prejudice test of Rule 403, excludable only if its
probative value is substantially outweighed by its unfairly
prejudicial effect. We need not decide whether Rule 403 or
Rule 703 governs in this case because we conclude that exclu-
sion of the evidence was not an abuse of discretion under
either rule.
  2
    Witness Boyko testified without objection that the EMFs extended
beyond the right of way. Gimmy also mentioned how EMFs extended
beyond the right of way, subject to a limiting instruction that his testimony
should be considered only insofar as it bears on the question of public per-
ception and how public perception affects land value.
7286               UNITED STATES v. CAMPION
  A.   Probative Value

   Circuit precedent provides meaningful guidance on the pro-
bative value of the measurements in question. In 706.807
Acres, the government condemned a safety buffer zone for
loading explosives on a 

. The land-
owner introduced expert testimony suggesting that severance
damages were appropriate because the buffer zone did not
provide adequate protection for the rest of his land. 

In reaching his conclusion, this expert relied upon
the opinion of another expert as to what was actually “safe.”

was admitted but the jury rejected it and
found no severance damages. When the landowner challenged
the verdict on appeal, the court held that the landowner failed
even to make out a prima facie case for severance damages
because there was no testimony connecting the safety issue to
the real estate market. 

relying on an expert’s
perception of a safety risk, the landowner should have intro-
duced evidence showing public perceptions of a safety risk.

of conditions on the property must
bear on market effects to be admissible. If the expert based his
opinion on nonpublic information and there was no showing
of what the public considered a safe buffer zone, the opinion
could not support a verdict for the plaintiff. While the ulti-
mate issue in that case was the sufficiency—rather than the
exclusion—of evidence, the court’s holding did not deal in
shades of sufficiency, stating that “[t]here is . . . no demon-
strated causal link between the taking of the [buffer zone] and
the severance damage of which the Trustees complain.” 

   [3] We conclude that this example governs our case. The
trial judge here required all EMF evidence to bear on public
perceptions and their market effect. This requirement was no
surprise to Campion: it was reiterated in a series of hearings
before and during trial that if Campion wished to introduce
                      UNITED STATES v. CAMPION                       7287
evidence of EMF levels, he would have to show the connec-
tion between those levels and public perceptions. Campion
declined the court’s repeated invitation, even when given an
extended opportunity to make an offer of proof.

   [4] Campion argues that he was deprived of a chance to
show the jury the premise of his claim—the fact that EMFs
do exist on the property. While public perceptions of danger
from power lines are, to some extent, predicated on the exis-
tence of EMFs in a given area, Gimmy’s testimony in the
record and his report do not suggest that EMF measurements
are relevant to public perceptions. The jury heard testimony
from two witnesses that EMFs existed. In the absence of rele-
vant and probative evidence, a jury could only speculate con-
cerning the effect of a particular measurement on public
perception. Perhaps the general public, unschooled in the sig-
nificance of the milligauss,3 is afraid of actual EMFs in any
quantity, so long as they come from a big power line. Or per-
haps the levels of EMFs that exist on Campion’s land would
even ease public fears in the marketplace. See 

simply no way for a jury to tell. Without any evidence from
Gimmy or anyone else that higher levels of EMF generate
higher levels of buyer aversion and lower sale prices, Sage’s
testimony about specific EMF levels has little to no probative
value.

  B.    Prejudice

   [5] Our inquiry next turns to the unfair prejudice that could
have resulted had Sage’s measurements been introduced. To
the extent that Sage’s testimony and illustration suggested that
  3
   One thousandth of a gauss; the unit Sage employed in her measure-
ments. The Oxford English Dictionary defines “gauss” as follows: “The
electromagnetic unit of magnetic induction (flux density) in the
[centimetre-gram-second] system, defined as the induction that exerts a
force of one dyne on each centimetre of a straight wire carrying one e.m.u.
(10 amp.) of current, when the induction is perpendicular to the wire.”
7288                   UNITED STATES v. CAMPION
certain levels of EMFs would burden or undermine the value
of his property, Campion failed to show how the EMF levels
in that witness-selected zone had a special influence on public
perceptions. There is a corresponding risk that Sage’s testi-
mony would mislead or confuse the jury; the testimony would
invite inferences about EMF levels that were unsupported—
whether they ran to Campion’s advantage or not.4 Given the
potentially prejudicial effect of the measurements and Campi-
on’s failure to establish their probative value, we hold that
their exclusion was not an abuse of discretion.5

IV. Studies Commissioned by Developers to Measure
EMFs

   The court prohibited Sage from describing the EMF studies
that developers had commissioned her to undertake or specific
instances where she had advised developers about EMFs. The
judge reasoned that “when people hear about number crunch-
ing, computer models, . . . et cetera, in order for that to have
some relevance, the underlying premise, that is, that EMF
causes some danger or harm, would be required.” While this
evidence is closely associated with the excluded measure-
  4
    At the hearing on October 28, 2005, the district judge described part
of the prejudice concern in a way that accords with his ultimate ruling:
      [T]he maps [showing EMF levels on Campion’s land] are obvi-
      ously a concern because I can envision a map where she has these
      red lines or something like that, which, again, as I’ve indicated,
      just really overemphasizes, with no factual basis, that there is this
      zone—not a zone of fear, but a zone of EMF transmissions,
      which implicitly cause harm. And that’s not what . . . this jury
      needs to be concerned about.
   5
     In evaluating the trial judge’s exercise of discretion, we note that the
government received parallel treatment with respect to mitigating evidence
it offered about EMFs that come from all kinds of electrical devices. The
government offered this evidence for purposes of impeachment of Gimmy,
and the court ruled that it was unfairly prejudicial under Rule 403 because
there had been no showing that home buyers generally take their default
EMF exposure from all kinds of electrical devices into account when eval-
uating the risk of living near power lines.
                  UNITED STATES v. CAMPION                7289
ments, separate analysis applies because it does not relate to
the market’s sensitivity to the result of Sage’s measurements,
but to the market’s sensitivity to the fact that some buyers
seek out Sage’s measurements in the first place. Because this
evidence held little probative value and any erroneous exclu-
sion of this evidence was harmless to the verdict, we affirm
the district court.

  A.   Probative Value

   [6] Testimony by Sage regarding her experience with
developers would have some probative value to the extent that
it reflects the perceptions of developers in general concerning
EMFs. When developers exhibit their anxiety by requesting
computer models, those requests may illustrate a form of pub-
lic perception. That perception exists regardless of whether
the results of Sage’s tests are reliable. Without inferring any
causal link between specific measurements and market behav-
iors, it is possible to infer that developers are concerned
because they commission these reports. The judge’s objection
—that computer modeling implies actual danger and scientific
accuracy—poses no obstacle to probative value. Sage’s com-
puter models and studies are direct evidence that those public
misapprehensions about EMF risk exist, at least in the view
of developers.

   [7] The probative value of the testimony would have added
relatively little, however, to the evidence that was presented
at trial. See Fed. R. Evid. 403 (balancing probative value
against “needless presentation of cumulative evidence”). The
judge did allow Sage to testify, by way of personal back-
ground, to the fact that she advises developers about EMFs
generally. This testimony included showing the jury a list of
Sage’s clients. The district judge forbade her to testify only
regarding specific instances where she advised developers and
other entities. The judge reasoned that Gimmy did not base
his expert testimony on Sage’s advice to specific developers.
The judge also noted that the impact of Sage’s advice on pub-
7290               UNITED STATES v. CAMPION
lic perceptions was unclear without surveys or some other
broad indicia of market effects. In light of the fact that the
judge did allow Sage to testify that she advised developers
generally, the marginal probative value of specific instances
of advice is minimized, particularly when there was no tie-in
to Gimmy’s testimony.

  B.   Unfair Prejudice and Harmless Error

   [8] The danger of confusion or prejudice from this testi-
mony is not as apparent as the danger relating to EMF mea-
surements and impairment zone maps, but it probably exists
in some degree because the jury might give it undue effect.
The balancing of factors for and against admissibility is close
enough so that we cannot say that the district court abused its
discretion in excluding this part of Sage’s testimony. Even if
we were to conclude to the contrary, however, reversal would
not be required. A non-constitutional error requires reversal
unless there is a “fair assurance of harmlessness, or stated oth-
erwise, unless it is more probable than not that the error did
not materially affect the verdict.” See United States v. Seschil-
lie, 

, 1214 (9th Cir. 2002) (internal quotation
marks and citation omitted). The perceptions of the develop-
ers with whom Sage came into contact were only one segment
of the total evidence of public perceptions, and they were
even a smaller segment of the overall evidence of diminished
value, which included visual, auditory, and other factors. In
light of the evidence’s limited probative value, and the fact
that the jury could infer that developers inquire about EMF
levels from other aspects of Sage’s testimony, it is more prob-
able than not that the exclusion of testimony on Sage’s spe-
cific experiences with developers did not materially affect the
verdict.

                       CONCLUSION

  The trial judge acted within his discretion in excluding
Sage’s measurements, as depicted in a map of the “impaired
                  UNITED STATES v. CAMPION              7291
zone,” on the ground that they could plausibly mislead the
jury into thinking that EMFs posed a proven health risk to
humans. The countervailing probative value of such measure-
ments is minimal because Campion presented no evidence
linking specific EMF levels with specific public perceptions
or market effects. With respect to the models Sage con-
structed for developers, these specific examples offer little
probative value in light of the general testimony regarding
Sage’s work that was admitted. If there was any error in
excluding the latter evidence, the error was harmless. The
judgment of the district court is

  AFFIRMED.