OPINION
EASTAUGH, Justice.
I. INTRODUCTION
We consider here various evidentiary rulings in a case arising out of a collision between a personal injury plaintiff's bicycle and the defendant's truck Because it was an abuse of discretion to exclude evidence of the plaintiff's pre-accident drug-seeking behavior, and because the error was prejudicial, we reverse the judgment against the defendant and remand for a new trial.
II. FACTS AND PROCEEDINGS
On July 2, 1997 a truck driven by Into Liimatta collided with a bicycle ridden by Deborah Vest. Vest suffered a broken right clavicle, trauma to her teeth and face, an avulsion fracture of her left wrist, and bruises and abrasions on the right side of her body. Vest sued Liimatta, seeking damages for past and future medical expenses, lost earnings, severe impairment, disfigurement, and noneconomic losses including pain and suffering, emotional distress, loss of enjoyment of life, fear, embarrassment, humiliation, and inconvenience. The jury returned a verdict awarding Vest damages of $97,287.26. On April 12, 1999 the superior court entered a final judgment of $119,219.91 against Lii-matta. Liimatta appeals and Vest cross-appeals.
[313]*313III. DISCUSSION
A. Standard of Review
We review a trial court's "decision to admit or exclude evidence for abuse of discretion."1 We find an abuse of discretion only when "left with a definite and firm conviction, after reviewing the whole record, that the trial court erred in its ruling.2
We review the superior court's set-off decision " 'de novo, adopting the rule of law that is most persuasive in light of precedent, reason, and policy' "3 The date when "prejudgment interest begins to accrue is a question of law which we review using our independent judgment."4
B. It Was an Abuse of Discretion to Exclude Evidence of Vest's Pre Accident Drug Seeking Condition.
Vest's medical history contains numerous references to drug-seeking behavior.5 Vest moved in limine to exclude evidence of her drug-seeking behavior. The trial court ruled that evidence of Vest's post-accident drug-seeking behavior was admissible, stating:
I can see that there are all sorts of relevancy issues here.
It refutes the claim of pain and suffering. That means-what that means is she really wasn't in pain, she was just seeking drugs when she went to these doctors and got these medications. It refutes the extent of her injuries: that is, these injuries are just a minor matter compared to the-her real motive, and that was to go get these drugs. And it increases her-the medical expenses exponentially, not for legitimate treatment for actual injuries, but because she's running around getting drugs from various doctors.
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... And I think there's sufficient relevancy here to ... outweigh the prejudice that's caused by this kind of information coming in.
But the trial court nonetheless excluded evidence of Vest's pre-accident drug-seeking behavior, reasoning that it was "redundant, repetitious, and highly prejudicial." Thus, the trial court apparently applied Alaska Evidence Rule 408, which provides: "Although relevant, evidence may be excluded if its probative value is outweighed by the danger of unfair prejudice, confusion of the issues, or misleading the jury, or by considerations of undue delay, waste of time, or needless presentation of cumulative evidence."
1. The danger of unfair prejudice did not outweigh the probative value of the evidence of Vest's pre-accident drug-seeking behavior.
When reviewing the exelusion of evidence under Evidence Rule 408 as unfairly prejudicial, we first "consider the relevance of the {[exeluded evidence] and then determine whether its prejudicial effect so outweigh[s] its probative value that admission by the trial judge constitute[s] a 'clear abuse of discretion. " 6
Liimatta argues that evidence of Vest's pre-accident drug-seeking behavior was highly relevant to damages, credibility, and causation. We agree.
Evidence of Vest's pre-accident drug-seeking behavior was highly relevant to Vest's claim for the loss of enjoyment of life. In Ocasio v. Amtrak, the plaintiff sued Am[314]*314trak for injuries sustained when a train struck him while he was walking on elevated railroad tracks.7 In addition to seeking damages for past and future medical expenses, the plaintiff sought to recover for the loss of enjoyment8 of The defendant offered evidence at trial that the plaintiff had a ten-year history of drug abuse problems involving cocaine, heroin, and alcohol which had continued until the accident.9 The trial court excluded the evidence, stating that its prejudicial effect outweighed its probative value with respect to the plaintiff's claim for loss of enjoyment of life.10 On appeal, the Superior Court of New Jersey, Appellate Division, reversed, holding that "a jury assigned the responsibility of determining the value of a loss of enjoyment of life should have had the opportunity to consider evidence that [a plaintiff's] mental and physical functions, customary activities and capacity to enjoy the pleasures of life were already restricted by a long-term addiction to drugs."11 Similarly, evidence of Vest's pre-accident drug-seeking behavior was highly relevant to her claim for the loss of enjoyment of life.
This evidence was also highly relevant to causation, because it would have helped the jury distinguish between medical expenses attributable to Liimatta's negligence and medical expenses attributable to Vest's drug-seeking behavior. For example, Liimatta correctly notes that
Vest claimed fees for the second, third and fourth opinions she sought for a shoulder surgery referral, despite the fact that all four opinions recommended against surgery. In assessing whether these repeated consultations were caused by the accident or caused by her drug-seeking condition, the jury would have to consider the true extent of her drug-seeking condition as it existed then, and not just the relatively minimal evidence in the short time between the date of the accident and these visits. The same applies to any of her post-accident medical care requests; the extent of Vest's drug-seeking condition was probative to the cause of each pain complaint and request for medication.
Evidence of Vest's pre-accident drug-seeking behavior was also relevant to her credibility. Vest testified at trial that she had not had a problem with addiction to pain medication before the accident. Thus, evidence of Vest's pre-accident drug-seeking behavior would have directly impeached her testimony. Vest's credibility was particularly relevant, because a critical trial issue was the legitimacy of Vest's post-accident subjective pain complaints; her credibility when testifying might have shed light on the credibility of her subjective complaints. Evidence of pre-accident drug-seeking behavior was also relevant to the credibility of Vest's expert witness. It would have tended to impeach Vest's expert, Dr. Bliss, who testified that Vest's subjective pain complaints were legitimate.
Liimatta also argues that the excluded evidence was relevant because, he asserts, Vest made an aggravation claim that encompassed drug-seeking behavior. Thus, according to Liimatta, Vest argued to the jury that it could award damages to Vest if it found that Liimatta's negligence had aggravated Vest's drug-seeking behavior. While we agree that such an aggravation claim would make evidence of Vest's pre-accident drug-seeking behavior relevant, it is not clear to what extent Vest made such a claim in this case. While Vest's brief does not deny that she made such a claim, our review of the record does not convince us that Vest squarely made this argument to the jury. We therefore do not rely on this argument as a basis for reversing. But an argument by Vest on remand that Liimatta's negligence aggravated her drug-seeking behavior would be an additional reason to admit the evidence.
Liimatta next argues that the danger of unfair prejudice did not outweigh the probative value of this evidence. We agree.
[315]*315In Hiller v. Kawasaki Motors Corp., we stated that undue prejudice "connotes not merely evidence that is harmful to the other party, but evidence that will result in a decision being reached by the trier of facts on an improper basis."12 Evidence of prior drug use and addiction certainly presents a danger of unfair prejudice.13 [There are strong attitudes against drug use. The introduction of evidence of drug use could cause the jury to consider ... [that] the person who uses drugs is a bad person and could prejudice his or her case."14 Despite undoubted resulting prejudice, however, the probative value of proffered evidence may compel its admission.15 For example, in CNA Insurance Co. v. Scheffey, the Court of Appeals of Texas held that "[It is difficult to imagine that a trial court would not abuse its discretion if, upon balancing pursuant to Rule 408, it determined that the probative value of evidence ... which bears on the crux of the case, was outweighed by a danger of unfair prejudice."16 As we noted above, evidence of Vest's pre-accident drug-seeking behavior was highly relevant to the central issues. It was therefore an abuse of discretion to exclude the evidence, despite its unsavory implications, as unfairly prejudicial.
2. Evidence of Vest's pre-accident drug-seeking behavior was not cumulative.
The superior court excluded this evidence partly because it was cumulative. Liimatta argues that it was an abuse of discretion to exclude the evidence for this reason. We agree.
In Wasserman v. Bartholomew, we held that two categories of evidence may properly be exeluded as cumulative: (1) evidence supporting an uncontested or established fact, and (2) evidence repeating a point made by previous evidence.17 We noted that "[elvi-dence falling within [the] second category should be excluded with caution, for repetition of the same evidence on a disputed point by several witnesses is often persuasive in establishing the truth of that evidence." 18 We also noted that excluding evidence pertaining to the central issue at trial on the ground that it is cumulative "is rarely within the trial court's discretion.19
Because Vest testified that she had not had a problem with addiction to pain medication before the accident, it was not an uncontested or established fact that Vest had engaged in pre-accident drug-seeking behavior. Furthermore, although the trial court admitted some evidence of Vest's pre-acci-dent drug-seeking condition-Dr. Totten was allowed to testify about "his concerns based on a history of [Vest's] drug-seeking behavior"-the excluded evidence did not repeat a point made by previous evidence, because any repetition of the evidence was itself relevant to the extent and severity of Vest's pre-accident drug-seeking condition.20 Finally, because Vest's pre-accident drug-seeking condition was relevant to the central disputes in the case, it was an abuse of discretion to exclude the evidence as cumulative.
3. There was adequate foundation for the introduction of evidence of Vest's pre-accident drug-seeking behavior.
Vest argues that the evidence was inadmissible because Liimatta did not offer expert [316]*316testimony to lay a proper foundation for its introduction. Vest cites Sweet v. Sisters of Providence, where we stated:
It is well established that trial courts have the right to ensure that proffered evidence meets certain legal thresholds before it may be used at trial. For instance, a court may inquire into whether certain evidence is relevant and material, and whether it merits exclusion under Alaska Evidence Rule 408. Itis also proper for the court to ensure that foundational requirements [are] satisfied.[21]
Vest's argument is not well taken, because the medical testimony at trial established the necessary foundation for admitting the evidence. Dr. Totten testified:
Q: And there's one note that we would all want to ask you about, Doctor.
It says: Note she has a long past history of-and it goes on. It says: Medication-seeking behavior. And I want to ask you some questions about that, sir.
What do you mean by "medication-seeking behavior"?
A: The-this is a loosely-defined term that's applied in interpersonal communications between doctors. There's no diagnosis, quote, attached to this, but it's a-it's a means of communicating between physicians that a patient has-has a habit of-of attending with complaints which a [physi-clan] is unable to substantiate objectively and the patient's request is for medications.
Furthermore, Dr. Paulson, an oral surgeon, agreed that patients with drug-seeking behavior will "sometimes go so far as to have their teeth extracted to enable that pain medicine behavior." Thus, there was adequate foundation in the record to support the admission of evidence of Vest's pre-accident drug-seeking behavior.
4. The error was prejudicial.
Vest argues that any error in excelud-ing this evidence was harmless. She claims that Liimatta was permitted to make his argument to the jury that Vest's damages "were more a product of her 'drug seeking behavior' than of any actual injuries she received in the collision." Vest notes that Lii-matta was allowed to present evidence of Vest's post-accident drug-seeking condition, and that Dr. Totten was allowed to testify about the history of his treatment of Vest, including his concerns about her drug-seeking behavior. Vest also claims that "[wJhat[ever] point there was to be made in the introduction of Mr. Liimatta's requested 'evidence' was made. Ms. Vest was not awarded the full measure of her requested past medical expenses, no damages for future loss of earning capacity and no damages for future physical impairment." (Emphasis deleted.)
Liimatta counters that because the exelud-ed evidence was directly relevant to the central disputes in the case, it cannot be said with fair assurance that the jury would not have been swayed if the evidence had been introduced.
The potential opportunity to cross-examine Vest herself about some of the exeluded records does not render the exclusion harmless. To the extent the records contain admissions Vest made to health professionals, her answers on cross-examination about the admissions could be effectively impeached only by showing the records to the jury, something that their exclusion apparently precluded. To the extent the records contained observations or opinions of health professionals, cross-examination of Vest would have been ineffective because she did not have the training to respond to such questions.
The dissent would affirm, partly because it concludes that Liimatta's failure to make an offer of proof deprived the trial court of an opportunity to rule on the probative value of particular documents.22 But there is no legitimate dispute that at least some of the pre-accident medical records that were excluded contained evidence which was highly relevant, as we have noted above. We read the trial court's exclusionary rulings to encompass these records and to have rendered [317]*317futile further attempts by Liimatta to admit them into evidence.
A judgment must be reversed under Alaska Civil Rule 61 if (1) evidence was erroneously excluded and (2) the exclusion prejudiced the offering party.23 An erroneous exclusion of evidence is prejudicial to the offering party if we cannot "say with fair assurance, after stripping the erroneous action from the entire evidence, that the jury was not substantially swayed or affected by the error."24 In making this determination, we "must necessarily put [ourselves], as nearly as possible, in the position of the jury in order to determine whether, as reasonable [peoplel, the error committed probably af fected their verdict."25 Because, as noted above, the excluded evidence was highly relevant to the critical disputes in this case, we cannot say with fair assurance that its exclusion did not sway or affect the jury. We therefore reverse the judgment and remand for a new trial. Any embarrassing information in the medical records which is not particularly relevant on remand may be redacted.
Because we reverse and remand for a new trial, we need not address Lifimatta's argument that the trial court erred by instructing the jury on aggravation of Vest's preexisting drug-seeking behavior after it exeluded this evidence. Remanding for a new trial alleviates any prejudice stemming from an untimely assertion of the aggravation claim.
C. It Was Not an Abuse of Discretion to Exclude Evidence of Vest's Receipt of Collateral Source Benefits.
Vest sought before trial to exclude evidence that she had received collateral source benefits-free medical and dental care at Southeast Alaska Regional Health Corporation, and eligibility for Medicare and Medicaid. The superior court excluded the evidence under the collateral source rule. Liimatta argues that it was an abuse of discretion to exclude the evidence for this reason without weighing its probative value against the dangers of unfair prejudice and confusion of the issues and the jury.
In Tolan v. ERA Helicopters, Inc., we held that evidence of the receipt of collateral source benefits is admissible "if offered for a purpose other than the diminution of the plaintiff's damages. When such an offer is made the court should not automatically admit or reject the evidence. -It must weigh its probative value against the dangers of unfair prejudice and confusion of the issues and the jury.26
Liimatta argued below that Vest's receipt of collateral source benefits was relevant to the issue of mitigation of damages. He claimed that Vest prolonged the period of her disability partly because she did not have to pay for medical and dental care. The trial court excluded evidence of Vest's collateral source benefits without explicitly weighing the probative value of the evidence against the dangers of unfair prejudice and confusion of the issues and the jury.27
Although the trial court excluded the evidence of Vest's receipt of collateral source benefits without explicitly balancing its probative value against the dangers of unfair prejudice and confusion of the issues and the jury, any error in failing to do so is harmless if balancing would have dictated exclusion of the evidence.28
Courts have recognized that evidence of a plaintiffs receipt of collateral source benefits is relevant to the issue of [318]*318malingering.29 Nevertheless, "it is usually acknowledged that the trial judge should exclude such evidence, or admit it only warily. Chief among [the] reasons is the possible prejudice to the plaintiff which attends informing the jury that [s/lhe has already received some ... compensation for the injuries complained of."30 Furthermore, "insofar as [such] evidence bears on the issue of malingering, there will generally be other evidence having more probative value and involving less likelihood of prejudice than the receipt of [collateral source benefits]."31 Because a balancing of the probative value of the evidence against the dangers of unfair prejudice and confusion of the issues and the jury would have dictated exclusion, any error was harmless.
D. It Was Not an Abuse of Discretion to Exclude Dr. Smith's Letter to the Social Security Disability Determination Unit.
Liimatta next argues that it was an abuse of discretion to exclude Dr. Kim Smith's letter to the Social Security Disability Determination Unit. Dr. Smith's letter concluded that "[tlhere didn't seem to be a great amount of impairment in [Vest]." The superior court excluded the letter because Dr. Smith had not been called as a witness to testify about it. Liimatta contends that Dr. Smith's letter was an admissible business record under Alaska Evidence Rule 808(6). We disagree.
Under Alaska Rules of Evidence 801 and 802, a statement, other than one made by the declarant while testifying at the trial or hearing, offered in evidence to prove the truth of the matter asserted, is hearsay and is inadmissible. But Rule 808(6) excepts from the hearsay rule:
A memorandum, report, record, or data compilation, in any form, of acts, events, conditions, opinions, or diagnosis, made at or near the time by, or from information transmitted by, a person with knowledge acquired of a regularly conducted business activity, and if it was the regular practice of that business activity to make and keep the memorandum, report, record, or data compilation, all as shown by the testimony of the custodian or other qualified witness, unless the source of information or the method or cireumstances of preparation indicate lack of trustworthiness.
Medical records kept by hospitals and doctors are often admitted under the business records exception.32 However, the evidence Liimatta proffered was not a medical record, but a letter sent by Dr. Smith to the Social Security Disability Determination Unit. Because Liimatta did not establish that "it was the regular practice" 33 of Dr. Smith to prepare and send evaluation reports to the Social Security Disability Determination Unit, the letter was not a business record admissible under Rule 803(6). It was therefore not an abuse of discretion to exelude the letter.
E. It Was an Abuse of Discretion to Exclude Evidence of Vest's Mental Disorders.
Vest moved in limine to exclude evidence of her preexisting mental disorders. Vest had been diagnosed with bipolar disorder and agoraphobia, and was incapable of working during eight years preceding the accident. The superior court granted Vest's motion, excluding evidence of Vest's mental disorders under Alaska Evidence Rule 408. Liimatta argues that it was an abuse of discretion to exclude this evidence because it was highly relevant to Vest's claim for future lost earnings. We agree.
[319]*319 Evidence of a plaintiff's preexisting mental disability is admissible when it is relevant to a claim for future loss of earning capacity.34 Indeed, the jury instructions on Vest's future loss of earning capacity claim stated that the jury "may consider [Vest's] health, physical and mental abilities her work habits and occupation before the accident...." (Emphasis added). Evidence of Vest's preexisting mental disabilities was also highly relevant to her past lost earnings claim. Such evidence would have tended to establish the extent to which Vest's post-accident, pre-trial inability to work was caused by Liimatta's negligence rather than Vest's preexisting mental disabilities. It was therefore an abuse of discretion to exclude the evidence.
F. It Was Not an Abuse of Discretion to Exclude the Medical Records Summary.
At trial, Liimatta sought admission of a summary of Vest's medical records and history under Alaska Evidence Rule 1006, which provides: "The contents of voluminous writings ... which cannot conveniently be examined in court may be presented in the form of a chart, summary, or caleulation." The trial court excluded the summary. Liimatta argues that it was an abuse of discretion to exclude the summary.
A Rule 1006 summary is admissible only if it accurately reflects the summarized evidence.35 The trial court found that the summary Liimatta sought to admit did not accurately reflect the medical records it purported to summarize, noting that "it dwelled very heavily on every negative thing that could be found." Because the medical records underlying the summary are not part of the record on appeal, we cannot independently determine the summary's accuracy and therefore have no basis for holding that it was error not to admit it into evidence.36 Since Liimatta has not demonstrated that the summary was accurate, we affirm its exclusion.
G. The Trial Court Properly Offset the Judgment by the Amount of Funds Advanced to Vest by Liimatta's Insurer.
Before trial, Liimatta's insurer advanced $10,214 to Vest under a written agreement that the payments would be credited to any judgment Vest obtained at trial or in settlement of her claim. The trial court accordingly offset the judgment by $10,214. In her cross-appeal, Vest claims that it was error to offset the judgment by the amount advanced to her.
Vest first contends that Liimatta is not entitled to an offset under AS 09.17.070,37 [320]*320because he cannot establish that the funds advanced were intended to compensate her for "the same injury"38 for which the jury awarded damages. Vest argues that the advanced funds were intended to compensate her for "undisputed damages" which she did not claim at trial, rather than the "disputed damages" which she litigated and the jury awarded.
Vest's reliance on AS 09.17.070 is misguided. That statute applies by its terms only to funds a plaintiff receives from "collateral sources."39 In Chenega Corp. v. Exxon Corp., we defined a collateral source as " 'a source [that] is entirely independent of and collateral to a wrongdoer who is legally responsible for the injuries' " to a plaintiff, and concluded that a tortfeasor's insurer is not a collateral source.40 The funds advanced by Liimatta's insurer were therefore not from a "collateral source," and AS 09.17.070 does not apply.
Furthermore, Vest's assertion that the advanced funds were intended to compensate her for "undisputed damages" which she did not claim at trial is inconsistent with the language of her written agreement with Litmatta's insurer. Each receipt Vest signed for funds advanced by Liimatta's insurer provides: "This amount is to be eredited to any final settlement or to the amount payable under our policy for any judgment which you may obtain as a result of your accident on July 2, 1997." That the advanced funds were to be credited to any judgment Vest received necessarily implies that the parties intended the advanced funds to compensate Vest for litigated damages.
Vest next argues that the receipts she signed for funds advanced by Liimatta's insurer do not give rise to an enforceable contract. Vest argues that "there is no evidence beyond the receipts and the payments themselves that she ever agreed to the terms contained in the language on the receipts." She further claims that Liimatta's insurer "never 'offered' to advance her money ... on the condition that she offset such advances against her eventual recovery" but rather "simply advanced the subject funds and informed her that such offset would occur." (Emphasis deleted.) Finally, Vest contends that because all of the language on the receipts was pre-printed, it is "not an expression of [her] agreement to the terms printed on the receipt, [but rather] a reflection of [Liimatta's insurer's] expectations."
Vest's arguments are unpersuasive. In Beluga Mining Co. v. State, Department of Natural Resources, we held that "the formation of a valid contract requires 'an offer encompassing all essential terms, unequivocal acceptance by the offeree, consideration, and an intent to be bound." 41 Here, the receipts Vest signed encompassed all of the essential terms of the offer, and Vest's signature is evidence of an unequivocal acceptance and an intent to be bound by those terms. And, as the trial court accurately noted, both parties received a legally bargained-for benefit and detriment:
State Farm was under no obligation to give Ms. Vest money before her claim was settled. It suffered a legal detriment by advancing her money before the close of her case-that is, it lost the use of that money and any interest that may have been earned on it. State Farm also received a benefit-Ms. Vest's promise to [321]*321credit the payments she received against any recovery on her claim.
Ms. Vest, too, received a benefit. She got the use of this money before her claim was settled. She also suffered a detriment in that she promised to reduce her recovery by the amount of the money that she was advanced.
Finally, Vest argues that her agreement with Liimatta's insurer is unenforceable under 3 Alaska Administrative Code (AAC) 26.060, which provides: "Any person transacting a business of insurance who participates in the investigation, adjustment, negotiation, or settlement of a claim: ... (4) may not request a first-party claimant to agree to a compromise or enter into a release that extends beyond the subject matter that gives rise to the claim payment...." (Emphasis added.) Vest asserts that the emphasized disjunctive "or" in 3 AAC 26.060(4) "permits a reading of the provision as forbidding [an] insurer from requesting that a first-party claimant agree to a compromise 'or from entering into any 'release that extends beyond the subject matter that gives rise to the claim payment.' " We decline to adopt this interpretation. Chapter 26 of Title 3 of the Alaska Administrative Code consistently specifies which of its provisions apply to first-party complaints, third-party claimants, or both.42 Because 3 AAC 26.060(4) does not specifically address third-party claimants, we hold that the regulation does not apply to Vest, who is a third-party claimant. We therefore conclude that the superior court properly offset the judgment under the enforceable contract between Vest and Liimat-ta's insurer.43
H. The Prejfudgment Interest Award Must Be Recalculated.
Liimatta argued below that prejudgment interest should not be assessed on the funds advanced to Vest for the period after Vest received the funds. The trial court nevertheless awarded prejudgment interest on the entire amount of the jury's past damages award ($79,887.26) from July 38, 1997-when Vest was infured-without accounting for the $10,214 advanced to Vest. Liimatta contends that part of the prejudgment interest award conferred a windfall double recovery upon Vest. We address this issue in anticipation that it might arise again on remand.
Because "money is worth less the later it is received[,] ... prejudgment interest is [awarded] to compensate [a] plaintiff for the loss of the use of the money from the date of injury until the date of judgment." 44 Prejudgment interest may not be awarded to the extent it would give the plaintiff a double recovery.45 "The party opposing a prejudgment interest award bears the burden to [322]*322show that a double recovery would result; otherwise prejudgment interest is awarded as a matter of course." 46
The trial court awarded Vest prejudgment interest on the entire amount of the jury's past damages award partly because it found that it was not clear whether the advanced funds were intended to compensate Vest for past damages (for which a plaintiff is entitled to prejudgment interest) or future damages (for which a plaintiff is not usually entitled to prejudgment interest).47 If the advanced funds were intended to compensate Vest for past damages, then part of the prejudgment interest award gave Vest a windfall double recovery, because Vest was no longer deprived of the use of the funds after she received them. To the extent that Liimatta establishes on remand that the advanced funds were intended to compensate Vest for past damages, the trial court should not award prejudgment interest on the funds for the period after Vest received them.
The trial court also noted that the parties' agreement provided for the advanced funds to be deducted from any subsequent "judgment," which by definition includes a prejudgment interest award.48 The trial court therefore ruled that "the judgment should be calculated and then the advances deducted." But the judgment should not include a prejudgment interest award to the extent it would give the plaintiff a double recovery.49 The parties' agreement is not inconsistent with limiting prejudgment interest to the periods when Vest was actually deprived of damages due her.
Finally, Vest claims that because the advanced funds were intended to compensate her for "undisputed damages" which she did not claim at trial, the prejudgment interest award does not give her a double recovery. But as we noted in Part III.G, Vest's assertion that the advanced funds were intended to compensate her for "undisputed damages" which she did not claim at trial is inconsistent with the language of her written agreement with Liimatta's insurer.
IV. CONCLUSION
Because it was an abuse of discretion to exclude evidence of the plaintiff's pre-acci-dent drug-seeking behavior, and because the error was harmful, we REVERSE the judgment against Liimatta and REMAND for a new trial. On remand, the trial court should offset any judgment Vest obtains by $10,214, the amount advanced by Liimatta's insurer. Moreover, to the extent that Liimatta establishes that the advanced funds were intended to compensate Vest for past damages, Vest should not recover prejudgment interest on the funds for the period after Vest received them.