June 16, 2025- Jennifer Thompson v. Presbyterian Healthcare Services, Inc., No. A-1-CA-40460

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IN THE COURT OF APPEALS OF THE STATE OF NEW MEXICO	1
Opinion Number:__________	2
Filing Date: June 16, 2025	3
No. A-1-CA-40460	4
JENNIFER THOMPSON, Personal	5
Representative of the ESTATE OF	6
GEORGE THOMPSON; and JERRY	7
POTTS, JR., Personal Representative	8
of the ESTATE OF JUDY THOMPSON,	9
Plaintiffs-Appellants,	10
v.	11
KATHLEEN LOPEZ, M.D.; BRIAN	12
MUMFORD, M.D.,	13
Defendants-Appellees,	14
and
PRESBYTERIAN HEALTHCARE SERVICES,	15
INC. d/b/a PRESBYTERIAN HOSPITAL;	16
PRESBYTERIAN MEDICAL GROUP;	17
CYNTHIA VALDEZ, M.D.;	18
JEFFREY P. ROSS, M.D.; and EDWARD	19
MCKENZIE, M.D.,	20
Defendants.	21
APPEAL FROM THE DISTRICT COURT OF BERNALILLO COUNTY	22
Nancy J. Franchini, District Court Judge	23
6/16/2025 12:22 PM

Curtis & Co.	1
Lisa K. Curtis	2
Andre K. Archuleta	3
Luke W. Holmen	4
Albuquerque, NM	5
Law Office of Jamison Barkley, LLC	6
Jamison Barkley	7
Santa Fe, NM	8
for Appellants	9
Atwood, Malone, Turner & Sabin, P.A.	10
Carla Neusch Williams	11
Roswell, NM	12
for Appellee Brian Mumford, M.D.	13
Rodey, Dickason, Sloan, Akin & Robb, P.A.	14
Holly Armstrong	15
Albuquerque, NM	16
for Appellee Kathleen Lopez, M.D.	17

OPINION	1
ATTREP, Judge.	2
{1} Plaintiffs appeal the judgment entered in favor of defendant radiologists after	3
a jury trial on their claims of medical negligence. Prior to trial, Plaintiffs dismissed	4
their claims against certain defendants. Now, on appeal, Plaintiffs raise claims of	5
error about dismissed and nonparty doctors. Specifically, Plaintiffs argue that the	6
district court (1) caused the jury to be confused when it denied Plaintiffs’ request to	7
interlineate the case caption to remove defendants who were dismissed prior to trial,	8
and then abused its discretion by instructing the jury, pursuant to Fahrbach v.	9
Diamond Shamrock, Inc., 1996-NMSC-063, 122 N.M. 543, 928 P.2d 269, about	10
Plaintiffs’ resolution of their claims against these defendants to alleviate the	11
confusion; and (2) erred by instructing the jury on the comparative negligence of	12
certain dismissed and nonparty doctors. As for Plaintiffs’ first claim of error, we	13
conclude that Plaintiffs have failed to establish the district court abused its	14
discretion. Any jury confusion about the dismissed defendants could not have been	15
avoided by the interlineation of the case caption because the defendant radiologists	16
raised an affirmative defense of comparative negligence as to some of the dismissed	17
defendant doctors, and we are not persuaded the district court erred by instructing	18
the jury pursuant to Fahrbach. As for Plaintiffs’ second claim of error, we conclude	19
any error in instructing the jury on comparative negligence was harmless because	20

2
the jury, in finding defendant radiologists not negligent, never reached the issue of	1
the comparative fault of the dismissed and nonparty doctors; prejudice is not	2
presumed under the circumstances of this case; and Plaintiffs have not otherwise	3
established they were prejudiced by the comparative negligence instructions.	4
Plaintiffs additionally claim on appeal that the district court erred in admitting	5
certain expert testimony. We conclude that any error in this regard was harmless.	6
We accordingly affirm.	7
BACKGROUND	8
{2} Mr. George Thompson died from sepsis as the result of a perforation of his	9
large bowel, after a two-week-long stay at Presbyterian Hospital. Plaintiffs, the	10
Estate of George Thompson and Judy Thompson1 (Mr. Thompson’s wife), sued	11
Presbyterian Healthcare Services, Inc. d/b/a Presbyterian Hospital; Presbyterian	12
Medical Group; and Drs. Kathleen Lopez (radiologist), Brian Mumford	13
(radiologist), Cynthia Valdez (hospitalist), Edward McKenzie (hospitalist), and	14
Jeffrey Ross (infectious disease specialist) for medical negligence based on the care	15
Mr. Thompson received at Presbyterian Hospital. Prior to trial, Plaintiffs settled their	16
claims against Presbyterian Healthcare Services, Inc. d/b/a Presbyterian Hospital,	17
1 Judy Thompson died before trial, resulting in the substitution of a new
personal representative for George Thompson’s estate and the substitution of the
Estate of Judy Thompson for Judy Thompson.

3
Presbyterian Medical Group, and Drs. Valdez and McKenzie; and the complaint was	1
dismissed with prejudice as to these defendants, as well as Dr. Ross.	2
{3} Plaintiffs sought to prove that the remaining defendant doctors, Drs. Lopez	3
and Mumford (collectively, Defendants), the two radiologists, were negligent in	4
their review and interpretation of CT scans. In the pretrial order, Defendants denied	5
they were negligent and argued that Drs. Valdez and McKenzie, the two hospitalists	6
against whom Plaintiffs settled, breached the standard of care, raising comparative	7
fault as a defense. At trial, Defendants maintained that they were not negligent and	8
that Drs. Valdez and McKenzie, as well as Dr. David Stryker, an infectious disease	9
specialist who was never named as a defendant in this case, breached the standard	10
of care and that this was the proximate cause of Mr. Thompson’s death. The jury	11
was instructed consistently with Defendants’ denial of negligence and affirmative	12
defense of comparative fault. The jury found that neither Defendant Lopez nor	13
Defendant Mumford were negligent, and accordingly did not allocate any fault to	14
Drs. Valdez, McKenzie, or Stryker. After post-trial motions, Plaintiffs appealed the	15
judgment entered in Defendants’ favor. We reserve further discussion of the	16
pertinent facts for our analysis.	17
DISCUSSION	18
{4} Plaintiffs argue that the district court: (1) abused its discretion by denying	19
their request to interlineate the case caption to remove the dismissed defendants and	20

4
then by informing the jury, pursuant to Fahrbach, about Plaintiffs’ resolution of their	1
claims against these defendants; (2) erred by instructing the jury on the comparative	2
negligence of Drs. Valdez, McKenzie, and Stryker; and (3) abused its discretion by	3
allowing Defendant Mumford to testify based on his specialized medical knowledge	4
and training without qualifying him as an expert witness, contrary to Rules 11-701	5
and 11-702 NMRA, and, in light of this error, abused its discretion by then admitting	6
cumulative expert testimony, contrary to Rule 11-403 NMRA. We discuss these	7
issues in turn.	8
I. Interlineation and the Fahrbach Instruction	9
{5} Prior to trial, Plaintiffs moved to interlineate the case caption to remove the	10
names of the defendants who previously were dismissed, and moved in limine, under	11
Rule 11-408 NMRA, to bar evidence of the settlements with the dismissed	12
defendants. Defendants opposed the motions, noting that the jury would hear about	13
the dismissed defendants because of Defendants’ comparative fault defense, and that	14
a Fahrbach instruction would reduce any jury confusion without prejudicing	15
Plaintiffs. The district court denied Plaintiffs’ motion to interlineate, noting that	16
“Plaintiffs have not cited to any case law or rule that directs the [c]ourt to	17
‘interlineate’ a caption when parties to a case have settled.” The district court	18
subsequently denied Plaintiffs’ motion in limine, determining that “[t]he potential	19
for juror speculation and confusion in this case is great as it relates to the settlement	20

5
and dismissal of other parties.”2 The district court concluded that this potential	1
confusion could be addressed by instructing the jury, pursuant to Fahrbach, that “a	2
settlement took place and that the jury is not to speculate upon the reasons for, or	3
content of, the settlement agreements.” The court gave the parties the opportunity to	4
submit proposed Fahrbach instructions.	5
{6} The district court selected Defendants’ proposed Fahrbach instruction, but	6
initially agreed, at Plaintiffs’ request, not to read the instruction to the jury until the	7
end of the trial. The Fahrbach instruction ended up being read to the jury on the	8
third day of trial, however, after the jury submitted a note asking the district court to	9
“explain if/how we will hear from the other defendants listed in this case other than	10
[Drs.] Mumford and Lopez[; and w]hy are we only considering the two of them.”	11
The full instruction given to the jury follows.	12
The only defendants at trial are Dr. Brian Mumford and Dr. Kathleen	13
Lopez. In addition to Dr. Mumford and Dr. Lopez, plaintiff also sued	14
Dr. Cynthia Valdez, Dr. Edward McKenzie, Dr. Jeffrey Ross, and	15
Presbyterian Health Services. Plaintiff resolved her claims against Dr.	16
Valdez, Dr. McKenzie, Dr. Ross, and Presbyterian Health Services.	17
You are not to speculate upon the reason for, or content of, such	18
resolution.	19
2The district court additionally explained that “the fact that some defendants
are no longer in the case because of settlement could be relevant and is allowed to
show a witness’s bias or prejudice under Rule 11-408(B).” See Rule 11-408
(providing that evidence of a settlement is not admissible “either to prove or disprove
the validity or amount of a disputed claim,” but such evidence may be admitted “for
another purpose, such as proving a witness’s bias or prejudice”).

6
{7} In Fahrbach, our Supreme Court held that a district court “may inform the	1
jury of the fact of settlement if the court has reason to believe (a) that it should do so	2
in order to assist the jurors in understanding their responsibilities, and (b) that it can	3
do so without prejudice to any party.” Id. ¶ 1. The district court in Fahrbach was	4
concerned that the jury would “find it confusing to be asked to allocate liability	5
among tortfeasors when, without explanation, some of the tortfeasors are not present	6
in court” because they had already settled with the plaintiffs prior to trial. Id. ¶ 3. In	7
an attempt to avoid such confusion, the district court informed the jury prior to voir	8
dire that the plaintiffs had sued three other parties who had settled and would not be	9
participating in the trial, but that “you will hear evidence concerning their conduct	10
and you will have an opportunity, if selected as a juror, to assess fault concerning	11
some or all of those parties.” Id. The plaintiffs argued this was error, id. ¶ 1, but the	12
Supreme Court concluded that district courts are not precluded by Rule 11-408	13
“from advising the jury, where appropriate, regarding a settlement that has	14
eliminated one or more parties.” Id. ¶ 12. Fahrbach concluded that the district	15
court’s decision to inform the jury of the other defendants and settlements was a	16
“proper[] attempt[] to eliminate what [the district court] reasonably perceived as	17
unnecessary [juror] confusion.” See id. ¶¶ 3, 21.	18
{8} On appeal, Plaintiffs argue that “it was an abuse of discretion for the trial court	19
to maintain the names of the dismissed parties in the caption and then give the	20

7
Fahrbach instruction to resolve any confusion about why their names were in the	1
case caption.” 3 The district court’s decision to interlineate the case caption is	2
inherently discretionary, and we review such a decision for an abuse of discretion.	3
See State v. Ferry, 2018-NMSC-004, ¶ 2, 409 P.3d 918 (“Discretion is the authority	4
of a district court judge to select among multiple correct outcomes.”); Talley v.	5
Talley, 1993-NMCA-003, ¶ 12, 115 N.M. 89, 847 P.2d 823 (“When there exist	6
reasons both supporting and detracting from a trial court decision, there is no abuse	7
of discretion.”). We likewise review the district court’s decision to instruct the jury	8
consistently with Fahrbach for an abuse of discretion. See 1996-NMSC-063, ¶¶ 1,	9
21. Plaintiffs bear the burden of establishing that the district court abused its	10
discretion. See Sundance Mech. & Util. Corp. v. Atlas, 1990-NMSC-031, ¶ 30, 109	11
N.M. 683, 789 P.2d 1250 (“The burden is upon the appellant to show that the trial	12
court abused its discretion, and this burden is a heavy one in view of the requirement	13
that there be a patent showing of abuse of discretion or manifest error in the trial	14
court’s exercise of that discretion.” (citations omitted)).	15
{9} Plaintiffs assert the confusion necessitating the Fahrbach instruction was	16
“created” by the district court’s “inclusion of the names of the dismissed parties in	17
3Defendants contend that Plaintiffs failed to preserve their arguments relating
to the Fahrbach instruction. Because we conclude that Plaintiffs have not established
error, we simply assume, without deciding, that they properly preserved this issue
for appellate review.

8
the caption,” and this confusion “would have been avoided by ministerially striking	1
the names of the parties dismissed before trial.” We are not persuaded. Contrary to	2
Plaintiffs’ assertion, any jury confusion relating to the dismissed defendants would	3
not have been eliminated by striking their names from the caption. Plaintiffs ignore	4
the fact that, consistent with the pretrial order, Defendants pursued a comparative	5
fault defense against Drs. Valdez and McKenzie, two of the dismissed defendants,	6
at trial,4 and that extensive testimony was elicited about the actions of the treatment	7
team, including Drs. Valdez and McKenzie. Thus, regardless of how the district	8
court ruled on Plaintiffs’ motion to interlineate, the fact of the dismissed defendants’	9
existence and their conduct would have become known to the jury, raising questions	10
and potential confusion for the jury about those defendants. See Fahrbach, 1996-	11
NMSC-063, ¶¶ 3, 16 (considering, under similar circumstances, the district court’s	12
observation that “jurors find it confusing to be asked to allocate liability among	13
tortfeasors when, without explanation, some of the tortfeasors are not present in	14
court”). Given this, Plaintiffs have not advanced a viable argument why the district	15
court’s denial of the motion to interlineate was an abuse of discretion. See Ferry,	16
2018-NMSC-004, ¶ 2; Talley, 1993-NMCA-003, ¶ 12.	17
4Although Plaintiffs separately challenge the comparative fault instructions
for lack of sufficient evidence, they do not contend on appeal that Defendants should
have been barred at the outset of trial from asserting a comparative fault defense.

9
{10} Recognizing the possibility that the jury would be confused by the dismissed	1
defendants, the district court determined that giving a Fahrbach instruction was	2
appropriate. Plaintiffs fail to advance any persuasive argument why this decision	3
prejudiced them or was otherwise erroneous. See Fahrbach, 1996-NMSC-063, ¶ 1	4
(holding that a district court “may inform the jury of the fact of settlement if the	5
court has reason to believe (a) that it should do so in order to assist the jurors in	6
understanding their responsibilities, and (b) that it can do so without prejudice to any	7
party”). Plaintiffs contend that the Fahrbach instruction “gave the jury the	8
impression Plaintiffs had already recovered for Mr. Thompson’s death, the settled	9
defendants had greater responsibility than Defendants for the death, that there was	10
something behind Defendants’ affirmative defenses of comparative fault, and that	11
Plaintiffs were litigious and not trustworthy.” The Supreme Court in Fahrbach	12
disregarded similar arguments, even though the jury in that case was informed that	13
the plaintiffs settled with absent defendants. See id. ¶ 3, 10. In this case, the jury was	14
merely informed that Plaintiffs “resolved” their claims against the absent defendants	15
and were specifically instructed, consistent with Fahrbach, see id. ¶ 17, “not to	16
speculate upon the reason for, or content of, such resolution.” Plaintiffs assume,	17
contrary to case law, that the jury disregarded the instruction not to speculate. See	18
Kilgore v. Fuji Heavy Indus. Ltd., 2009-NMCA-078, ¶ 26, 146 N.M. 698, 213 P.3d	19
1127 (“We presume that the jurors followed the instructions given by the court.”).	20

10
Further, Plaintiffs themselves speculate about the effect of the Fahrbach instruction	1
on the jury in this case. This is insufficient to satisfy Plaintiffs’ burden on appeal.	2
See Fahrbach, 1996-NMSC-063, ¶ 32 (concluding that speculation that “the	3
improper charge to the jury influenced the outcome of the case” was insufficient to	4
establish reversible error (internal quotation marks omitted)); Nat’l Educ. Ass’n of	5
N.M. v. Santa Fe Pub. Schs., 2016-NMCA-009, ¶ 15, 365 P.3d 1 (“General	6
assertions of prejudice are insufficient to demonstrate prejudice.”). Plaintiffs	7
otherwise argue that the Fahrbach instruction should not have been given in favor	8
of simply striking the dismissed defendants’ names from the caption. Having already	9
determined this would not have eliminated the jury confusion, we have no basis to	10
conclude that the district court abused its discretion in giving the Fahrbach	11
instruction. See Ferry, 2018-NMSC-004, ¶ 2; Talley, 1993-NMCA-003, ¶ 12.	12
II. The Comparative Fault Instructions	13
{11} Plaintiffs’ principal argument on appeal is that the district court erred by	14
instructing the jury on the comparative negligence of Drs. Valdez, McKenzie, and	15
Stryker. Plaintiffs contend this was erroneous because (1) Defendants did not present	16
sufficient evidence that Drs. Valdez, McKenzie, and Stryker breached the standard	17
of care; and (2) Defendants contravened the pretrial order by relying on one of	18
Plaintiffs’ testifying experts as proof of Drs. Valdez, McKenzie, and Stryker’s	19
negligence, instead of the experts listed in the pretrial order, and by failing to	20

11
“provide any notice of Defendants’ assertion of the defense of comparative liability	1
as against [Dr.] Stryker.” Defendants argue that Plaintiffs failed to preserve their	2
challenges to the comparative fault instructions; regardless, the instructions were	3
proper; and even if the instructions were erroneous, they were harmless and	4
accordingly do not merit reversal. Because we agree with Defendants that any error	5
in instructing the jury on comparative fault did not prejudice Plaintiffs and that	6
prejudice is not presumed under the circumstances of this case, we simply assume,	7
without deciding, that there was error and limit our analysis to an examination of	8
harmless error.5
9
{12} Generally speaking, the party complaining about instructional error on appeal	10
has the burden of showing that the error was prejudicial—i.e., that the erroneous	11
instruction influenced the jury’s verdict. See Kennedy v. Dexter Consol. Schs., 2000-	12
5Plaintiffs did not preserve their second argument that instructing the jury on
comparative fault contravened the pretrial order. In support of preservation,
Plaintiffs cite their motions for a directed verdict, reconsideration, and a new trial.
Plaintiffs’ motion for a directed verdict and subsequent motion for reconsideration,
however, were premised on a lack of sufficient evidence to instruct the jury on
comparative fault, not on a contravention of the pretrial order. Given this, Plaintiffs’
motion for a new trial, which raised the arguments relating to the pretrial order for
the first time, was insufficient to preserve these issues. See Kilgore, 2009-NMCA-
078, ¶ 50 (“Generally, a motion for a new trial cannot be used to preserve issues not
otherwise raised during the proceedings.”); Sandoval v. Baker Hughes Oilfield
Operations, Inc., 2009-NMCA-095, ¶ 56, 146 N.M. 853, 215 P.3d 791 (“Generally,
a motion for a new trial cannot be used to preserve issues not otherwise raised during
the proceedings.”). We accordingly limit our consideration of whether there was
harmless error to Plaintiff’s first argument that insufficient evidence existed to
instruct the jury on comparative fault.

12
NMSC-025, ¶¶ 26-27, 129 N.M. 436, 10 P.3d 115 (providing that “[a]n error is	1
harmless unless the complaining party can show that it created prejudice,” and that	2
a judgment will not be set aside “based on mere speculation that an erroneous jury	3
instruction influenced the outcome of the case”); Vigil v. Miners Colfax Med. Ctr.,	4
1994-NMCA-054, ¶ 9, 117 N.M. 665, 875 P.2d 1096 (“On appeal, it is the	5
appellant’s burden to show that the instruction given was erroneous and	6
prejudicial.”).	7
{13} In this case, the jury found that Defendants were not negligent and, as a result,	8
never reached the issue of the comparative fault of Drs. Valdez, McKenzie, and	9
Stryker. The first question on the special verdict form asked the jury whether it found	10
“either or both defendant(s) negligent” and prompted the jury to answer with either	11
a “Yes” or “No.” The jury answered “No.” Based on this response, the special verdict	12
form instructed the jury not to answer the remaining questions on the form and	13
instead “have the foreperson sign this form and return it to the [b]ailiff.” The	14
question allocating fault—the last question on the special verdict form—was not	15
answered by the jury, presumably because the jury “understood and complied with	16
the court’s instructions.” See Britton v. Boulden, 1975-NMSC-029, ¶ 6, 87 N.M.	17
474, 535 P.2d 1325; see also Kilgore, 2009-NMCA-078, ¶ 26.	18
{14} Under such circumstances—where the jury resolved the question of liability	19
in the defendant’s favor and consequently did not decide the question of allocation	20

13
of fault—our case law is clear that any error in instructing the jury on comparative	1
fault is harmless. See Lewis ex rel. Lewis v. Samson, 2001-NMSC-035, ¶¶ 31 n.2,	2
41, 131 N.M. 317, 35 P.3d 972 (concluding that the district court’s comparative fault	3
instruction, “even if erroneous, would constitute harmless error” because the jury	4
“found by special verdict that [the d]efendants were not negligent” and thus “did not	5
reach the issue of apportionment of fault”); Norwest Bank N.M., N.A. v. Chrysler	6
Corp., 1999-NMCA-070, ¶¶ 6, 13-15, 127 N.M. 397, 981 P.2d 1215 (holding that	7
any error in a special verdict form’s comparative fault allocation instruction was	8
harmless because the jury determined, prior to allocating fault, that the defendants’	9
actions were not a proximate cause of the plaintiffs’ injuries); see also Fahrbach,	10
1996-NMSC-063, ¶ 33 (concluding that “because the jury found that [the defendant]	11
was not negligent, the [comparative fault] instructions . . . were harmless”); Ramos	12
v. Rodriguez, 1994-NMCA-110, ¶¶ 15-16, 118 N.M. 534, 882 P.2d 1047 (citing	13
approvingly “[t]he general rule applied by courts in other jurisdictions” that a jury’s	14
“finding that there was no proximate cause between the negligence of a defendant	15
and the injuries suffered by a plaintiff[] renders any additional jury findings	16
concerning the allocation of the percentage of fault to be mere surplusage”). Under	17
the foregoing authority, any error in instructing the jury on comparative negligence	18
was harmless because the jury resolved the question of liability in Defendants’ favor,	19
and, as a result, comparative fault was not at issue.	20

14
{15} Plaintiffs attempt to avoid this result by arguing that a different line of case	1
law, in which prejudice is presumed when a jury instruction is not supported by	2
sufficient evidence, applies. Plaintiffs’ premise is that the Lewis/Norwest line of	3
cases did not involve instructions unsupported by evidence and that when sufficient	4
evidence to support a jury instruction is absent, a presumption of prejudice arises.	5
Contrary to Plaintiffs’ suggestion, however, a presumption of prejudice does not	6
automatically arise, without further inquiry, in every case in which a jury instruction	7
lacks sufficient evidentiary support. See First Nat’l Bank in Albuquerque v. Sanchez,	8
1991-NMSC-065, ¶ 14, 112 N.M. 317, 815 P.2d 613 (questioning whether the	9
plaintiff was prejudiced by the submission to the jury of a duress claim that was not	10
supported by substantial evidence, and stating that the Court was “inclined to think	11
the erroneous submission of the duress claim to the jury does not present a case of	12
reversible error,” despite the rule of law that “when a party has submitted to the jury	13
instructions providing alternative bases for relief, it is reversible error to submit any	14
one alternative for which there is no substantial evidence” (alteration, internal	15
quotation marks, and citation omitted)); cf. Kennedy, 2000-NMSC-025, ¶ 29	16
(acknowledging that dicta in Gerety v. Demers, 1974-NMSC-010, 86 N.M. 141, 520	17
P.2d 869, has been interpreted to support, in some situations, “assum[ing] prejudice	18
where a jury instruction states a proposition of law not supported by evidence,” but	19
declining “[t]o expand Gerety to apply to technically erroneous jury instructions”	20

15
because this “would create a virtual per se rule of reversible error for any and all	1
erroneous jury instructions and would threaten to remove jury instructions from the	2
ambit of the doctrine of harmless error”); Britton, 1975-NMSC-029, ¶ 7	3
(acknowledging the holding in a prior case “that the failure of a trial court to instruct	4
upon all correct legal theories presented and supported by substantial evidence	5
constitutes reversible error,” but limiting the reach of this holding because the prior	6
case was “concerned with legal theories relative to the question of liability” and	7
clarifying that “[i]t was not suggested that error in instructions on the question of	8
damages, which is never reached by the trier of the facts, constitutes reversible	9
error”).	10
{16} An examination of Chamberland v. Roswell Osteopathic Clinic, Inc., 2001-	11
NMCA-045, 130 N.M. 532, 27 P.3d 1019, on which Plaintiffs principally rely, is	12
instructive. Although the Court in Chamberland presumed prejudice because “the	13
[district] court erred in giving an instruction unsupported by the evidence,” id. ¶ 26,	14
the breadth of this holding is limited when the circumstances of Chamberland are	15
considered. Chamberland involved the situation where the jury was instructed on	16
independent intervening cause, and the jury returned a verdict for the defendants,	17
finding on the special verdict form that the defendants’ negligence was not the	18
proximate cause of the plaintiff’s injuries. See id. ¶¶ 1, 9-10, 17-19, 26. At the time,	19
“proximate cause” was defined in the uniform jury instructions as “that which in a	20

16
natural and continuous sequence unbroken by an independent intervening cause	1
produces the injury, and without which the injury would not have occurred.” UJI	2
13-305 NMRA (1987) (emphasis added) (brackets omitted); see also Chamberland,	3
2001-NMCA-045, ¶ 23 (discussing UJI 13-305 (1987)). Thus, unlike here, the jury’s	4
verdict in Chamberland, which rested on causation grounds, necessarily involved	5
the jury’s consideration of the erroneous independent intervening cause instruction.	6
See 2001-NMCA-045, ¶¶ 9-10, 17-19, 23. Given this, it was impossible to tell in	7
Chamberland whether the jury’s verdict was based on the improper instruction,	8
making presumptive prejudice appropriate. See Bachicha v. Lewis, 1987-NMCA-	9
053, ¶ 16, 105 N.M. 726, 737 P.2d 85 (“[W]here we cannot tell whether the jury	10
based its verdict upon an improperly submitted issue, the proper procedure is to	11
reverse and remand for a new trial on all issues.”); Garcia v. S. Pac. Co., 1968-	12
NMSC-085, ¶¶ 8-9, 79 N.M. 269, 442 P.2d 581 (providing that instructional error	13
was “prejudicial” where “[t]here is no way to tell what proportion, if any, of the	14
verdict was a result of this error”); First Nat’l Bank in Albuquerque, 1991-NMSC-	15
065, ¶ 14 (explaining that reversible error occurs when “an appellate court has no	16
way of knowing whether the jury relied upon the invalid basis in making its	17
decision”). Chamberland is in contrast with Zia Trust, Inc. v. Aragon, 2011-NMCA-	18
076, ¶ 28, 150 N.M. 354, 258 P.3d 1146, which likewise involved an erroneous	19
intervening cause instruction. In Zia Trust, however, “[t]he jury returned the special	20

17
verdict form . . . , stating that [the d]efendant was not negligent.” Id. Because the	1
jury never reached causation, “the district court’s instruction on independent	2
intervening cause was not an issue and therefore the instruction, even if improper,	3
was not prejudicial and therefore constituted harmless error.” Id.; see also Kennedy,	4
2000-NMSC-025, ¶ 28 (concluding that an instructional error was harmless because,	5
based on the jury’s verdict, it was clear that “[t]he error did not affect the jury”).	6
{17} Similar to Zia Trust, Inc., because the jury in this case never allocated fault,	7
the comparative negligence instructions were not an issue. See 2011-NMCA-076,	8
¶ 28. Given this, and because Plaintiffs fail to cite authority where prejudice was	9
presumed under such circumstances, we are not persuaded by Plaintiffs’ argument	10
that a presumption of prejudice extends to the circumstances of this case. See In re	11
Adoption of Doe, 1984-NMSC-024, ¶ 2, 100 N.M. 764, 676 P.2d 1329 (“We assume	12
where arguments in briefs are unsupported by cited authority, counsel after diligent	13
search, was unable to find any supporting authority. . . . Issues raised in appellate	14
briefs which are unsupported by cited authority will not be reviewed by us on	15
appeal.”). Nor have Plaintiffs otherwise established that instructing the jury on	16
comparative fault was prejudicial. See Kennedy, 2000-NMSC-025, ¶¶ 26-27; Vigil,	17
1994-NMCA-054, ¶ 9. In support of their claim that they were prejudiced, Plaintiffs	18
principally rely on a note sent by the jury during deliberations asking whether it was	19
to rule “on a percentage for the other doctors, despite hearing nothing about or from	20

18
them in the trial.”6 Before the judge could respond, however, the jury communicated	1
that they did not “need an answer to this question because they reached a verdict.”	2
From the jury question, Plaintiffs contend, “The jury may well have started to	3
conclude Defendants were liable and then shrunk away from the whole exercise	4
because they did not have the information to evaluate whether the non-parties were	5
negligent, and how to allocate fault among . . . them.” It seems just as plausible that	6
the jury question came about because the jury found no defendant negligent and	7
wondered if they were supposed to fill out the allocation of fault portion of the	8
special verdict form before realizing the jury instructions answered this inquiry for	9
them.	10
{18} Plaintiffs’ speculation about the jury’s decision-making process is plainly	11
insufficient to establish prejudice from the comparative fault instructions. See	12
Fahrbach, 1996-NMSC-063, ¶ 32 (concluding that speculation that “the improper	13
charge to the jury influenced the outcome of the case” was insufficient to establish	14
6Plaintiffs also point to the combined effect of the caption with the absent
defendants, the Fahrbach instruction, and Defendant Mumford’s testimony, which
we address next. Without explicitly saying so, Plaintiffs invoke the cumulative error
doctrine. To the extent this is their argument, we conclude they have failed to
demonstrate cumulative error “[g]iven our resolution of the [other] issues” they raise
on appeal. See Richardson v. Rutherford, 1990-NMSC-015, ¶ 17, 109 N.M. 495, 787
P.2d 414 (concluding that the appellant “failed to show the existence of cumulative
error” where the Court held that other issues raised on appeal were either not error
or were harmless error); cf. State v. Samora, 2013-NMSC-038, ¶ 28, 307 P.3d 328
(“Where there is no error to accumulate, there can be no cumulative error.”
(alteration, internal quotation marks, and citation omitted)).

19
reversible error (internal quotation marks omitted)); cf. Bachicha, 1987-NMCA-053,	1
¶ 15 (holding that “handwritten notations [by the jury] do not provide a basis for	2
determining how the jury reached a verdict for [the] defendant”). Furthermore,	3
Plaintiffs’ argument requires us—based on a note the jury quickly disclaimed—to	4
disregard the well-established presumption that jurors follow jury instructions. See	5
Britton, 1975-NMSC-029, ¶ 6; Kilgore, 2009-NMCA-078, ¶ 26. The instructions	6
and the special verdict form directed the jury that Plaintiffs had to prove all of the	7
elements of negligence, that Defendants denied that they were negligent, that each	8
defendant should be considered separately, and that comparative fault should not be	9
considered unless Defendants were found to be negligent. We decline to assume that	10
the jury did otherwise.	11
{19} In sum, the jury never reached the issue of comparative fault, prejudice is not	12
presumed under the circumstances of this case, and Plaintiffs have not otherwise	13
established prejudice from the comparative negligence instructions. We therefore	14
conclude that any error in instructing the jury on comparative fault was harmless.	15
III. Defendant Mumford’s Testimony	16
{20} Lastly, Plaintiffs argue that the district court improperly admitted certain	17
expert testimony. Specifically, Plaintiffs argue Defendant Mumford’s testimony	18
about “[w]hether a colon looks normal or abnormal in size,” “the difference between	19
an oblique and a transverse measurement,” and whether a demonstrative video was	20

20
accurate was improperly admitted as lay testimony under Rule 11-701 when in fact	1
it was expert testimony governed by Rule 11-702. In light of this error, Plaintiffs	2
contend that allowing expert testimony from one of Defendant Mumford’s expert	3
witnesses was cumulative of Defendant Mumford’s expert testimony, contrary to	4
Rule 11-403. Defendants argue that Plaintiffs failed to preserve these arguments and	5
that the admission of the challenged testimony was otherwise proper. Because	6
Plaintiffs have failed to meet their burden of demonstrating they were prejudiced by	7
the challenged testimony, we simply assume, without deciding, that Plaintiffs	8
preserved their objections and there was error, and we limit our analysis accordingly.	9
{21} “The complaining party on appeal must show the erroneous admission of	10
evidence was prejudicial in order to obtain a reversal.” Kilgore, 2009-NMCA-078,	11
¶ 64 (alteration, omission, internal quotation marks, and citation omitted). “This	12
burden includes having to show a high probability that the improper evidence may	13
have influenced the factfinder.” Id. (internal quotation marks and citation omitted).	14
Plaintiffs do not present any explanation of how the testimony in question may have	15
improperly affected the jury’s verdict as to Defendants’ negligence. See Headley v.	16
Morgan Mgmt. Corp., 2005-NMCA-045, ¶ 15, 137 N.M. 339, 110 P.3d 1076	17
(providing that “[w]e will not review unclear arguments, or guess at what [a party’s]	18
arguments might be”). Instead, the extent of Plaintiffs’ prejudice argument is that	19
permitting Defendants to “augment their testimony by putting on duplicative experts	20

21
and providing [cumulative] Rule 11-702 evidence” “compounded” the prejudice	1
from other alleged errors related to the comparative fault issue. This argument does	2
not explain how testimony about Defendants meeting the standard of care, even if	3
cumulative, is prejudicial in relation to the comparative fault of the dismissed and	4
nonparty doctors and is otherwise insufficient to meet Plaintiffs’ burden to	5
demonstrate prejudice. See Kilgore, 2009-NMCA-078, ¶ 64; see also Nat’l Educ.	6
Ass’n of N.M., 2016-NMCA-009, ¶ 15 (“General assertions of prejudice are	7
insufficient to demonstrate prejudice.”). We therefore conclude that the challenged	8
testimony does not warrant reversal.	9
CONCLUSION	10
{22} For the forgoing reasons, we affirm.	11
{23} IT IS SO ORDERED.	12
______________________________	13
JENNIFER L. ATTREP, Judge	14
WE CONCUR:	15
____________________________	16
ZACHARY A. IVES, Judge	17
____________________________	18
KATHERINE A. WRAY, Judge	19