593 P.2d 871 (1979)

CATERPILLAR TRACTOR CO., Appellant,
v.
Paula BECK, Appellee.
Paula BECK, Cross-Appellant,
v.
CATERPILLAR TRACTOR CO., Cross-Appellee.

Nos. 3066, 3068.

Supreme Court of Alaska.

April 6, 1979.

*874 Lloyd I. Hoppner of Rice, Hoppner & Hedland, Fairbanks, Murphy L. Clark, Anchorage, for appellant and cross-appellee.

Theodore R. Dunn of Matthews, Dunn & Baily, Anchorage, O. Nelson Parrish of Parrish Law Office, Fairbanks, for appellee and cross-appellant.

Before BOOCHEVER, Chief Justice, RABINOWITZ, CONNOR, and BURKE, Justices, and DIMOND, Senior Justice.

OPINION

CONNOR, Justice.

On June 24, 1973, Derald Allen Beck was killed when the Caterpillar 944 front-end loader which he was operating rolled over an embankment. Decedent's widow, Paula Beck, brought this action against Caterpillar Tractor Company (hereinafter Caterpillar) for the wrongful death of her husband. Beck contended that Caterpillar's failure to equip the 944 loader with a roll-over protective shield (hereinafter ROPS) constituted a design defect in the loader, and because of that defect, Derald Beck suffered fatal injuries. Following a jury verdict in favor of Beck, judgment was entered against Caterpillar in the amount of $408,594.50. Caterpillar appeals from this judgment, specifying several errors by the trial court. Beck cross-appeals, alleging that it was error for the trial court to instruct the jury on Derald Beck's comparative negligence.

I. FACTS

The model 944 front-end loader was designed by Caterpillar in the late 1950's and was first sold in 1964. It was the first model of Caterpillar's wheel loaders to be produced, and subsequent models have now replaced it. The particular loader involved in the accident was originally delivered by Caterpillar in 1964 to a dealer, Northern Commercial Company, as a standard model machine without a cab.

At the time of the accident, Derald Beck was a partner in R.W. Beck & Sons, d/b/a Nenana Excavators. Nenana Excavators bought the 944 loader as used equipment from the Northern Commercial Company in 1967. The ten ton loader was equipped with a fiberglass all-weather shell, without supporting members, which was attached by bolts to the body of the machine.^[1]

Although there were no witnesses to the accident, an investigating state trooper testified that Derald Beck was apparently "roading" the loader in reverse,^[2] with the bucket in a raised position. The road was dirt and gravel with soft shoulders and wound around the side of a hill. On one side of the road there was an embankment of approximately seven feet. The trooper estimated that Beck was traveling at approximately *875 10 to 15 miles per hour as he proceeded up the road, but the loader then sank into the road shoulder and came almost to a complete stop. The loader apparently rolled over on its side and then flipped over 180 degrees and fell down the embankment.^[3] Beck was crushed beneath the loader, pinned between the steering wheel and part of the seat. The fiberglass canopy was flattened out and parts of it were broken off.

Paula Beck, decedent's wife and personal representative, filed suit against Nenana Excavators for negligence in failing to provide safe equipment and against Caterpillar in strict liability. She alleged that Caterpillar's failure to manufacture the loader with a ROPS rendered the loader defective. Caterpillar denied that the loader was defectively designed because roll bar protective devices were not readily available at the time of design and because the loader was intended to be marketed as a basic structure to which the user, through his dealer, would add auxiliary parts as necessary for his particular use. Nenana Excavators was subsequently dismissed from the suit on its motion for a directed verdict because Derald Beck was a partner in the company and was, therefore, precluded from suing himself.

A ROPS is an overhead protective canopy which is constructed to withstand a roll-over and, thus, protect the operator from being crushed. In addition, a ROPS can decrease the risk of a roll-over. There was no dispute at trial that a ROPS, as developed at the time of the accident, would have saved Derald Beck's life. Beck would not have been crushed and a ROPS may have even prevented the loader from over-turning. There was also no dispute that it is best from a cost and technological standpoint to have a ROPS installed by the loader manufacturer at the time of initial production. However, there was considerable dispute about the availability of a ROPS at the time Caterpillar produced this loader in 1964.

Various types of protective canopies were used in the heavy equipment industry for many years prior to the development of a ROPS, particularly in the logging industry. These canopies provided protection primarily from inclement weather and falling objects. Such devices were known in the industry by the name FOPS, falling object protective shield or structure. These shields were manufactured by several auxiliary equipment manufacturers at the time the 944 loader was produced. A FOPS did not have the capability to withstand a roll-over.

A consulting safety engineer, Ovid Holmes, appearing as an expert for Beck, testified that the heavy equipment industry began testing ROPS devices as early as 1961. Holmes had not heard of a FOPS, but testified that he believed that some of the canopies developed in the 1950's did have roll-over protection capability. Although other front-end loader manufacturers did not supply a ROPS as part of the standard equipment at that time, several auxiliary equipment manufacturers did offer them.

According to Holmes, two Caterpillar dealers in California were selling an auxiliary ROPS by 1961 and the Illinois Division of Highways, in the home state of Caterpillar, had installed such structures on some of its equipment in 1962. Holmes believed that there was nothing technologically difficult about manufacturing a ROPS in 1964, but that Caterpillar did not do so because it would have been too costly. An employee of an auxiliary equipment manufacturer also testified that pre-1965 canopies were available with roll-over protection capability. Further, he stated that some of the canopies available in 1956-1960 for overhead protection were mounted to the frame of the basic machine in such a manner that the risk of roll-over was minimized.

*876 On the other hand, Caterpillar stated in its answer to an interrogatory of Beck, that "[p]rior to 1966, Caterpillar Tractor was not aware and is not aware of the availability of [ROPS] from anyone in the country." Although one Caterpillar senior staff engineer confirmed the Illinois Division of Highway utilization of ROPS, a manager of sales development, Jack Hasten, testified that he was unsure whether the Illinois canopy actually was a ROPS. Hasten also testified that the structural integrity of the type of canopies available in 1964 was such that it would have been irresponsible for Caterpillar to install them and represent them as having roll-over protection capability. In addition, he stated that there had been no need expressed for a ROPS. He claimed that users disliked attached canopies because the machines had a myriad of uses, some of which did not require a ROPS, and that a ROPS could be dangerous because it obstructed the operator's view and impeded his ability to jump free if the loader fell into water. Other Caterpillar staff engineers testified that there was no ROPS capability available at the design stages of the 944 loader.

Caterpillar, at the time of design and production of the 944 loader, made a "deliberate decision" not to install any kind of protective canopy whatsoever on the 944 as part of its basic design. It did begin testing the ROPS concept in 1966. By that time, several auxiliary equipment manufacturers were regularly producing ROPS. In response to various state and federal regulations promulgated shortly thereafter,^[4] Caterpillar, in 1969, began installing ROPS as part of the basic vehicle model. No ROPS was ever made part of the 944 model manufactured by Caterpillar and the 944 loader went out of production in 1968 before Caterpillar began adding ROPS to its loaders.

By special verdict, the jury found that the absence of a ROPS was a design defect in the 944 loader and that such defect proximately caused the death of Derald Beck. Damages were set at $817,189.00. However, the jury also found that Derald Beck knew of the design defect and voluntarily and unreasonably proceeded to use the defective product. Since the jury deemed Beck to be 50% at fault for the accident by his knowing confrontation of the risk of harm, the total amount of damages awarded was reduced by half.

Appellant Caterpillar contends in this appeal that the trial court erred by (1) improperly instructing the jury on the law of strict liability for alleged design defects and refusing to define "defect" for the jury; (2) improperly instructing the jury on the law of comparative negligence; and (3) refusing certain evidence offered by Caterpillar during the course of the trial to show Caterpillar's marketing methods and decedent Beck's knowledge of the availability of a ROPS from another source. Each of these issues raise important questions in the area of products liability. As we explain below, we agree with Caterpillar's objection to some of the challenged instructions and evidentiary rulings and conclude that the judgment must be reversed.^[5]

II. DESIGN DEFECT

Caterpillar contends that the trial court erred in instructing the jury that "[a] design defect is one in which the product, however perfectly manufactured, incorporates or fails to incorporate a design feature with the result that injury is proximately caused thereby."^[6] Caterpillar argues that *877 the instruction misconstrues the law of strict liability in that it essentially instructs the jury on absolute liability: it does not instruct the jury that they must first find a defect in the product nor does it give the jury guidance in determining whether a defect exists. In addition, Caterpillar urges that we define the term "defective" for cases involving design defect, preferably by use of a standard which balances the risk presented by the product in light of the product's utility. Beck, in response, argues that the jury was properly instructed on the necessity of finding a defect before it could fix liability and that the term "defect" need not be defined beyond its inherent meaning.^[7] Because this issue poses so substantial a question in a nascent body of law, we believe it would be helpful, before turning to the particulars of this instruction, to briefly summarize the development of products liability.

Strict products liability evolved from two separate bases: implied warranty and strict liability in tort.^[8] In the process whereby the courts have combined these theoretical bases and have fashioned from them a new species of product liability, it has become apparent that several policy considerations have been at work.^[9] First, greater efficiency and justice would be achieved by eliminating the necessity for plaintiffs to prove fault by manufacturers of defective products. Section, frustration of consumer expectation would still be the underlying basis of recovery. Third, incidence of harm from unsafe products would be reduced by imposing strict liability and thus providing an incentive to produce safer products. Fourth, risks would be allocated and losses spread by requiring a manufacturing enterprise to accept responsibility in strict liability for harm attributable to a defect in its product. The concept of risk allocation has been the primary policy rationale convincing courts to adopt strict products liability.^[10]

We adopted strict products liability in Clary v. Fifth Avenue Chrysler Center, Inc., 454 P.2d 244 (Alaska 1969), holding that:

"A manufacturer is strictly liable in tort when an article he places on the market, knowing that it is to be used without inspection for defects, proves to have a *878 defect that causes injury to a human being."^[11]

Following the doctrinal approach taken by the California Supreme Court in Greenman v. Yuba Power Products, Inc., 59 Cal.2d 57, 27 Cal. Rptr. 697, 377 P.2d 897 (1962), California's seminal products liability decision, we stated that:

"The purpose of imposing such strict liability on the manufacturer and retailer is to insure that the cost of injuries resulting from defective products are borne by the manufacturers that put such products on the market rather than by the injured persons who are powerless to protect themselves."^[12]

We reaffirmed this policy of risk allocation in subsequent products liability decisions. See Cloud v. Kit Manufacturing Co., 563 P.2d 248, 250 (Alaska 1977); Bachner v. Pearson, 479 P.2d 319, 327 (Alaska 1970).

Later, in Butaud v. Suburban Marine & Sporting Goods, Inc., 543 P.2d 209 (Alaska 1975) (hereinafter Butaud I,) we adopted the holding of the California Supreme Court in Cronin v. J.B.E. Olson Corp., 8 Cal.3d 121, 104 Cal. Rptr. 433, 501 P.2d 1153 (1972). Cronin, addressing the plaintiff's burden of proof in showing a defect, rejected the standard proposed by the Restatement (Second) of Torts^[13] that the plaintiff demonstrate that the product's defect rendered it "unreasonably dangerous." Rather, it held that a plaintiff satisfies his burden of proof when he proves the existence of a "defect" and that such defect was a proximate cause of his injuries.^[14]Cronin, 104 Cal. Rptr. at 438-442, 501 P.2d at 1158-62. This standard applies to cases wherein the alleged defect is one of design as well as one of manufacture.^[15]Cloud v. Kit Manufacturing Co., 563 P.2d 248 (Alaska 1977); Hauter v. Zogarts, 14 Cal.3d 104, 120 Cal. Rptr. 681, 534 P.2d 377 (1975); Henderson *879 v. Harnischfeger Corp., 12 Cal.3d 663, 117 Cal. Rptr. 1, 527 P.2d 353 (1974).

We turn now to Caterpillar's first objection to the trial court's instructions to the jury; i.e., that the trial court mistakenly instructed the jury in absolute liability.

Although courts and commentators have struggled with diverse approaches to strict products liability,^[16] most authorities appear to agree that manufacturers are not absolute insurers of their products.^[17] Strict liability will not impose legal responsibility simply because a product causes harm.^[18] A product must be defective as marketed if liability is to attach, and "defective" must mean something more than a condition causing physical injury.

The instruction at issue stated that plaintiff Beck alleged that a design defect caused the death of Derald Beck and then proceeded to state that a product is defectively designed when an injury results from a design feature (or the lack of a design feature). Essentially, the jury was instructed that there must be proof of a defect in the product's design in order for liability to attach, and that proof of an injury could suffice to prove a defect. If such defect proximately caused the injury, strict liability is imposed. This is a tautology and tantamount to an instruction of absolute liability.

Beck argues that the instruction was proper because it "simply advises the jury that a design defect is a defect resulting from a design feature." However, it is not just any design feature yielding an injury which will result in the imposition of legal responsibility for the incidents of such injury. A product is not necessarily defective merely because an injury occurred. Baker v. Chrysler Corp., 55 Cal. App.3d 710, 127 Cal. Rptr. 745 (1976). As Chief Justice Traynor of the California Supreme Court explained:

"The reasons justifying strict liability emphasize that there is something wrong, if not in the manufacturer's manner of production, at least in his product ... A bottling company is liable for the injury caused by a decomposing mouse found in its bottle. It is not liable for whatever harm results to the consumer's teeth from the sugar in its beverage. A knife manufacturer is not liable when the user cuts himself with one of its knives. When the injury is in no way attributable to a defect there is no basis for strict liability."^[19]

Likewise, it is not just the absence of any possible safety device which will render a product legally defective.

Beck contends that, even if the subject instruction were erroneous, the error was cured by other instructions which clearly required the jury to find that a defect existed. Other instructions did direct the jury that they must find that Beck had proven a defect in order to return a verdict in her favor. However, the only guidance the jury was given in how they should determine if the absence of a ROPS was a design defect was the above-quoted instruction. Even though the instructions as a whole required the jury to find a defect, the circular definition of a design defect was erroneous.

*880 Caterpillar also contends that the jury was inadequately instructed on the meaning of design defect. Since a manufacturer's strict liability depends upon the meaning of defective, Caterpillar urges us to develop particular standards for assessing a product's defectiveness.^[20]

Design defects present the most perplexing problems in the field of strict products liability because there is no readily ascertainable external measure of defectiveness. While manufacturing flaws can be evaluated against the intended design of the product, no such objective standard exists in the design defect context. Beck argues that, despite the lack of an external standard in design defect cases, the word "defect" has an inherent meaning; i.e., a flaw or incompleteness. Therefore, when jurors are instructed that they must find a defect to impose liability, they realize that the product must be faulty. However, we believe that the dictionary meaning of the word "defect" is insufficient to fully explain to the jury when a manufacturer should incur legal responsibility for his product's design.

"[The] natural application [of the word `defective'] would be limited to the situation in which something went wrong in the manufacturing process, so that the article was defective in the sense that the manufacturer had not intended it to be in that condition. To apply it also to the case in which . .. the design turns out to be a bad one or the product is likely to be injurious in its normal condition . .. [and] [t]o use it without defining it to the jury is almost to ensure that they will be misled." (footnotes omitted)

Wade, On the Nature of Strict Tort Liability for Products, 44 Miss.L.J. 825, 831-32 (1973). Since we are unwilling to view any product which causes an injury while being used properly as defectively designed, we must formulate a test which will guide the jury in design defect cases.^[21]

In the strict liability context, the term "defect" is "neither self-defining nor susceptible to a single definition applicable in all contexts." Barker v. Lull Engineering Co., Inc., 20 Cal.3d 413, 143 Cal. Rptr. 225, 235, 573 P.2d 443, 453 (1978). The varied purposes and the theoretical underpinnings of implied warranty and strict liability in tort have generated five main tests for product defectiveness: (1) the "deviation from the norm" test;^[22] (2) the "reasonable fitness for intended purpose" test;^[23] (3) the Restatement test; (4) the "risk/utility analysis" test;^[24] and (5) the recent test proposed by the California Supreme Court in Barker v. Lull Engineering Co., Inc., supra.

*881 Before determining which test for defect is the most appropriate, we must address Beck's claim that to define defect is inconsistent with our position in Clary^[25] and Butaud I.^[26] In many products liability cases, the approach taken in Clary will suffice for advising the jury when liability can be properly fixed. However, those decisions were neither all-encompassing nor intended to be read as precluding any further refinement of the defectiveness standard. We are also not restricted by the holding of Cronin,^[27] establishing the plaintiff's burden of proof, which we adopted in Butaud I.

"Cronin did not purport to hold that the term `defect' must remain undefined in all contexts, and did not preclude a trial court from framing a definition of defect, appropriate to the circumstances of a particular case, to guide the jury as to the standard to be applied in determining whether a product is defective or not." [citation omitted]

Barker v. Lull Engineering Co., Inc., supra, 143 Cal. Rptr. at 234, 573 P.2d at 452. Thus, because of the additional problems presented by design defect cases, we must now add a further dimension to our previous products liability decisions.

Under the "deviation from the norm" test, the product is classified as defective because it does not match the quality of most similar products.^[28] While this test may be reliable in a case involving a manufacturing defect, it is inadequate for those cases where the plaintiff contends that an entire product line is defectively designed.^[29] Comparison with similar products manufactured by others, while helpful, would be improper if used as the definitive test for ascertaining a defect.^[30] The test may also be overinclusive in some fact settings; *882 e.g., where "unavoidably unsafe products" are involved.^[31] In addition, the burden of proving the deviation would fall on the plaintiff. Since one of the major goals of strict products liability is to relieve the plaintiff of the burdensome evidentiary requirements of the negligence cause of action, this test would unduly burden the plaintiff.

The "unfitness for intended purpose" test of defectiveness originated "as a basis for deciding when purchasers could recover from sellers for intangible financial and commercial losses" resulting from frustration of the purchaser's expectations as to what the product would do.^[32] It was intended as a test to determine when a manufacturer would be liable for injuries caused by its products; but the adaptation of the test from commercial expectations suggests that the only basis for liability is consumer expectations.^[33] Accordingly, plaintiffs are more likely to recover when the danger is hidden than when it is patent. This is unacceptable because we have already determined that any distinction between patent and latent defects is unnecessarily restrictive to plaintiffs. See Butaud v. Suburban Marine & Sporting Goods, Inc., 543 P.2d 209, 214 (Alaska 1975); Luque v. McLean, 8 Cal.3d 136, 104 Cal. Rptr. 443, 448-449, 501 P.2d 1163, 1168-69 (1972).^[34] Also, this test operates to shield a defendant from liability as long as the product does not fall below the ordinary customer's expectations as to the product's safety. Consumer expectations are a factor to be considered in determining defectiveness, but the public policy supporting strict liability would be poorly served if consumer expectations were the sole boundary of liability.^[35]

The Restatement (Second) of Torts, section 402A, provides a two-prong test for the seller's liability. Defectiveness is established if the product leaves the seller's hands in an "unreasonably dangerous" condition and such condition is not contemplated by the ultimate consumer.^[36] Thus, recovery would not be allowed for obvious or generally known dangers. Although the Restatement test improves upon the deficiencies of the above tests, we adhere to our previously expressed view that the "unreasonably dangerous" terminology of the Restatement unnecessarily limits the scope of *883 liability and unduly increases the plaintiff's burden of proof.^[37]

Two commentators, Deans Page Keeton and John Wade,^[38] have proposed similar risk/utility analysis tests. Their approaches recognized that evaluation of product defectiveness involves multiple factors, and they attempt to fulfill the purposes of strict products liability by creating a framework for balancing the relevant factors without shifting the inquiry to what the manufacturer should have foreseen at the time the product was sold.

Dean Wade asserts that it is possible to use "a tort way of thinking and tort terminology" in relation to strict products liability — "to abandon the warranty way of thinking and its terminology" reflected in the "unfitness for intended purpose" test — without eroding the purposes served by strict liability and without retreating to negligence.^[39] He would have the trial court first determine, by comparing product risk with product utility, whether it would be reasonable to allow the jury to find for the plaintiff. If so, the jury would then be instructed as follows:

"A [product] is not duly safe if it is so likely to be harmful to persons [or property] that a reasonable prudent manufacturer [supplier], who had actual knowledge of its harmful character would not place it on the market. It is not necessary to find that this defendant had knowledge of the harmful character of the [product] in order to determine that it was not duly safe."^[40]

Dean Keeton's approach is that a product is defective if it is unreasonably dangerous as marketed. It is unreasonably dangerous if a reasonable person would conclude that the magnitude of the scientifically perceivable danger as it is proved to be at the time of trial outweighed the benefits of the way the product was designed and marketed. Under the heading of benefits one would include anything that gives utility of some kind to the product; one would also include the infeasibility and additional cost of making a safer product.^[41]

Because a conclusion of "defectiveness" represents a determination that the design at issue is "wrong" in the sense that we will impose legal responsibility for harm caused therefrom, we are in agreement with Deans Wade and Keeton that the final assessment of "defectiveness" necessarily implies a weighing of diverse factors related to the product's desirability and to its dangerousness. Since evidence of these factors will be considered by the jury, we believe it is preferable to provide the jury with a proper framework in which to consider such evidence. However, we perceive no reason to reinsert negligence terminology into the analysis by instructing the jury, as suggested by Deans Wade and Keeton, to determine what a reasonable, prudent manufacturer would have done if aware of the harmful nature of the product. The focus of strict products liability is on the condition of the product, not on the manufacturing and marketing decision of the defendant. Bachner v. Pearson, 479 P.2d 319, 325 (Alaska 1970).^[42] Therefore, *884 indiscriminate use of reasonableness language will confuse the strict liability standard by introducing inessential attention to the conduct of the defendant, even if actual knowledge of the harmful condition is presumed rather than proven. Nor do we think it necessary to have a two-tier system where the trial judge, before giving the case to the jury, must first find that it would be reasonable for the jury to find for the plaintiff. Given proper instructions, we believe a jury can determine from the evidence whether a defect exists or not.

The California Supreme Court held in Barker v. Lull Engineering Co., Inc., supra, that:

"[A] trial judge may properly instruct the jury that a product is defective in design (1) if the plaintiff demonstrates that the product failed to perform as safely as an ordinary consumer would expect when used in an intended or reasonably foreseeable manner, or (2) if the plaintiff proves that the product's design proximately caused his injury and the defendant fails to prove ... that on balance the benefits of the challenged design outweighed the risk of danger inherent in such design."

143 Cal. Rptr. at 239, 573 P.2d at 457-58.^[43] This dual approach was conceived in recognition of the multiplicity of "injury-producing deficiencies" encompassed within the word "defect". Id. at 235, 573 P.2d at 453. Following the California court's decision in Cronin, wherein the court did not purport to define "defect" but rather left the problem to be resolved by "resort to a cluster of useful precedents,"^[44] the California Courts of Appeal devised many different tests to define product defectiveness.^[45] Synthesizing the various approaches taken by the Courts of Appeal in dealing with particular "defect" situations, the California Supreme Court devised the above-quoted two-prong definition of defectiveness. Again, as in Cronin, the court was not attempting to formulate a mechanistic definition applicable to all situations. Rather, Barker directs the trial courts to formulate instructions which would elucidate the meaning of "defect," within the contours of the two-prong definition, in the circumstances of the cases presented to them.

In view of the diversity of product deficiencies which could fall within the notion of defect, we are persuaded that the Barker two-prong test provides the most comprehensive guidelines for instructing juries, without compromising any of the goals of strict liability.

The Barker test represents a composite of the most workable features of each of the other tests.^[46] The first prong of the Barker *885 test — that a product is defectively designed if it fails "to perform as safely as an ordinary consumer would expect when used in an intended or reasonably foreseeable manner"^[47] — incorporates notions of the implied warranty of fitness for reasonable use, a primary concept in the evolution of strict products liability,^[48] but eases the burden of proof on the plaintiff. In a cause of action based upon a warranty of fitness and merchantability, the plaintiff would have to prove the breach by pinpointing the actual defect.^[49] Under the Barker test, the plaintiff need only show, for strict liability to apply, that he used the product in an intended or reasonably foreseeable fashion and the product failed to perform in that capacity as safely as expected. Thus, this test, while giving content to the meaning of "defect," preserves the policies we expressed in Clary.^[50]

The second prong of the Barker definition encompasses those situations, such as the lack of a safety device which is presented here, where the product satisfies ordinary consumer expectations as to its general use but is still "defective" in that its design exposes the user or bystander to "excessive preventable danger."^[51] What is excessive preventable danger must turn on the facts of each case. With the focus off the ordinary consumer's expectations, the trier of fact balances the risk and the social utility of the product. This requires a weighing of various factors. Therefore, where necessary, the trial court may instruct the jury that if "on balance, the benefits of the challenged design outweigh the risk of danger inherent in such design," no liability will attach. Barker, supra, 143 Cal. Rptr. at 240, 573 P.2d at 458.

Although we believe that a balancing process is inevitable in certain design defect cases, we in no way intend to diminish our adherence to the goals of strict products liability. Therefore, we also agree with the position taken by Barker regarding the allocation of the burden of proof:

"[I]nasmuch as ... a manufacturer who seeks to escape liability for an injury proximately caused by the product's design on a risk-benefit theory should bear the burden of persuading the trier of fact that its product should not be judged defective, the defendant's burden is one affecting the burden of proof, rather than simply the burden of producing evidence." (citations omitted)

143 Cal. Rptr. at 237, 573 P.2d at 455. We hold that the plaintiff need only show that he was injured and that the injury was proximately caused by the product's design. The defendant may then avoid liability for a defectively designed product by proving by a preponderance of the evidence that, "on balance, the benefits of the challenged design outweigh the risk of danger inherent in such design." Barker, supra, 143 Cal. Rptr. at 240, 573 P.2d at 458. This will require the fact-finder to consider and compare a number of competing factors, including but not limited to,

*886 "the gravity of the danger posed by the challenged design, the likelihood that such danger would occur, the mechanical feasibility of a safer alternative design, the financial cost of an improved design, and the adverse consequences to the product and to the consumer that would result from an alternative design."

143 Cal. Rptr. at 237, 573 P.2d at 455. Besides lessening the burdens of the plaintiff's prima facie case, this allocation puts the burden of producing the relevant complex and technical evidence on the party who has the most access to and is the most familiar with such evidence.^[52]

Beck protests that adding further content to the meaning of product defectiveness will be a retreat to negligence concepts, will increase the plaintiff's burden of proof, and will create a distinction between manufacturing and design defects. As we have stated above, we intend no retreat from our holdings in Clary and Butaud I. Negligence concepts will not dilute the plaintiff's case because the trier of fact will concentrate on the nature of the product in determining defectiveness rather than upon the conduct of the defendant.

"Thus, the fact that the manufacturer took reasonable precautions in an attempt to design a safe product or otherwise acted as a reasonably prudent manufacturer would have under the circumstances, while perhaps absolving the manufacturer of liability under a negligence theory, will not preclude the imposition of liability under strict liability principles if, upon hindsight, the trier of fact concludes that the product's design is unsafe to consumers, users, or bystanders." (citation omitted)

Barker, supra, 143 Cal. Rptr. at 239, 573 P.2d at 457. The plaintiff's prima facie case in strict liability will not be made more onerous. The plaintiff's prima facie case essentially remains the same whether the defect is one in manufacturing or in design. Our holding merely reflects that the concept of defectiveness covers a diversity of product characteristics and, because we are not willing to affix liability solely on the basis of an injury-producing product, we will allow the trial courts to formulate instructions which elucidate the concept of "defect" in the particular circumstances presented.

In summary then, we hold that the instruction approved in Clary will in many cases suffice. However, in those cases where the meaning of "defect" will be unduly vague, particularly in design defect cases, the trial court may formulate instructions which define the legal concept of "defect" for the jury. Following the guidelines set by the Barker court, we hold that the trial court may instruct the jury that a product is defectively designed if:

"(1) the plaintiff proves that the product failed to perform as safely as an ordinary consumer would expect when used in an intended or reasonably foreseeable manner, or (2) the plaintiff proves that the product's design proximately caused injury and the defendant fails to prove, in light of the relevant factors, that on balance the benefits of the challenged design outweigh the risk of danger inherent in such design."

143 Cal. Rptr. at 234, 573 P.2d at 452. Because the jury here was erroneously instructed on causation as the primary definition of defect, the judgment entered against appellant Caterpillar must be reversed.

Caterpillar also contends the trial court erred in refusing seven of its proposed instructions. Although Beck argues that Caterpillar waived its objection to the court's refusal to give the requested instructions, our revie