SCHULTZ, Justice.
The issue presented in this action is whether a trial court has discretion to relieve an unwilling expert witness, who is a stranger to the litigation, from providing opinion testimony during a pretrial discovery deposition. Since we determine a litigant does not have an absolute right to compel an unwilling expert to give an opinion on facts outside the expert’s personal knowledge, we hold that a trial court has discretion to either relieve or compel such testimony depending on the circumstances presented in a particular case.
[238]*238This original certiorari action arises from a district court order compelling the plaintiff, Edward E. Mason, M.D., to respond to deposition questions involving his expertise in the field of gastric by-pass surgery. Although the district court is the nominal defendant in this proceeding, Mitchell, a medical malpractice plaintiff, is the interested party and has assumed defense of this action.
Dr. Mason’s involvement in the present dispute had its origin in a medical malpractice action currently pending in Davis County, Iowa. Plaintiff in that action, Vicki Mitchell (executor of her husband’s estate) alleged that the decedent, Ronald Mitchell, died as a result of negligence by three doctors and three nurses in their performance of gastric by-pass surgery. During the deposition of one of the defendant doctors, (Dr. Schiebe), Mitchell learned that the doctor had provided factual information about the surgery and its subsequent complications to the National Bariatric Surgery Registry at the University of Iowa Hospitals and Clinics. Dr. Mason is the director of the registry and a professor of surgery at the University of Iowa College of Medicine.
After learning of this exchange between the two doctors, Mitchell subpoenaed Dr. Mason to take his deposition in Johnson County. Although Mason appeared at the deposition, he refused to answer any questions concerning the information he had received from Dr. Schiebe. He felt the information was confidential since it was acquired in his capacity as director of the registry. Subsequently, Mitchell sought an order from the district court in Johnson County compelling Dr. Mason to answer not only questions regarding the factual information Dr. Mason had acquired, but also to give his expert opinion on the medical care received by the decedent in malpractice action. The district court, Judge Paul J. Kil-burg, ruled the information given to Dr. Mason as head of the registry was not privileged pursuant to Iowa Code sections 135.40-.42 and directed Dr. Mason to answer deposition questions concerning this information. The court refused to compel any discovery of Dr. Mason involving his expertise since he had not been consulted by either party as an actual or prospective witness.
After this ruling, Mitchell amended her answers to interrogatories in her Davis County action to indicate that she intended to call Dr. Mason as an expert witness. She again subpoenaed Dr. Mason and also sent him a check for the statutory expert witness fee pursuant to Iowa Code section 622.-72. One day before the scheduled deposition Dr. Mason informed Mitchell that he was not willing to testify as an expert in the action. At the deposition, he answered all questions involving the factual information but repeatedly refused to answer any questions based on his expertise.
Mitchell again filed an application in Johnson County District Court. Specifically, she requested an order compelling Dr. Mason “to answer any and all of plaintiff’s counsel’s questions concerning his general knowledge of the area of gastric by-pass surgery and . .. regarding his general opinion as to the care received by Mr. Mitchell.... ” Dr. Mason filed a resistance to the application supported by affidavit asserting that he was not a party to the case, he was not a treating physician in the case and he did not have an opinion concerning the medical treatment provided in the case, that he was not able to formulate an opinion concerning the standards of medical care applicable to this case without an extensive review of the medical literature and an examination of the medical records, that his testimony would jeopardize the research of the National Bariatric Surgery Registry, that his preparation and testimony in this case would interfere with his responsibilities at University Hospital, and that other experts were available to render opinions concerning the standard of care provided the decedent in this case. The matter was apparently submitted to the district court with the briefs and arguments of the parties but without any hearing or further record.
In response to Mitchell’s application, the defendant district court, Judge L. Vern [239]*239Robinson, ordered Dr. Mason to answer deposition questions about the general standard of care in this type of surgery and any hypothetical questions about the particular standard of care received by decedent in the underlying medical malpractice action. The court also ordered the parties to negotiate the amount of compensation Dr. Mason would receive for his expert testimony. It did not require Dr. Mason to engage in any pre-testimonial preparation or investigation.
In its ruling on the motion to compel, the trial court principally relied on Iowa Rules of Civil Procedure 122(a) and 140(a). Taken literally, the language of these two rules permits deposition discovery from any person on any relevant matter that is not privileged. The court concluded expert testimony was relevant to the issues in the underlying malpractice action and expert witnesses do not enjoy any testimonial privilege in Iowa. Given the parameters of our discovery rules as well as the common law principle of the “public’s right to everyman’s evidence,” the trial court apparently felt it lacked discretion to deny the motion to compel. Because we do not agree, the writ of certiorari is sustained.
Initially, we are confronted with the issue of whether a distinction should be made between compelling an unwilling expert to testify at trial as opposed to such compulsion in the pretrial discovery context. Normally the scope of discovery is not limited to evidence that would be admissible at trial. Iowa R.Civ.P. 122(a). The parties in their respective briefs have relied upon case authority involving expert compulsion in both pretrial and trial situations. Additionally, courts considering whether to compel expert testimony in discovery proceedings generally have not relied on any distinction between discovery and trial testimony in resolving the issue. In re New York Municipal Securities Litigation, 30 F.R.S.2d 842 (S.D.N.Y.1980) (magistrate’s report subsequently adopted by district court); Wright v. Jeep Corporation, 547 F.Supp. 871 (E.D.Mich.1982); Young v. Metropolitan Dade County, 201 So.2d 594 (Fla.App.1967). Finally, while arguments could be made that these situations are factually and legally distinct, fairness dictates that an expert not be required to expend time and effort during the discovery process if he could not be compelled to testify at trial.
We conclude, in these limited circumstances, the right to compulsory discovery should be no broader than the right to compel the same expert to testify at trial. Accordingly, a trial court has the same authority to determine the need for and issue protective orders in the discovery context as it would at trial. Having disposed of this corollary issue, we now turn to consideration of the central issue involved in this case.
Mitchell contends a party has a right to opinion testimony as long as it does not require the expert to engage in any preparation. Thus, she reasons the district court order adequately protected Dr. Mason since it did not require him to do any extra work. Moreover, she claims the order conforms to our liberal construction of discovery rules and our strict construction of testimonial privileges. Finally, Mitchell insists the plaintiff is asking this court to engraft a testimonial privilege based on expert status onto our discovery rules.
The plaintiff characterizes the issue somewhat differently. Basically, he argues litigants do not have an absolute right to the expert of their choice. In particular, a party to a medical malpractice action does not have the right to compel previously unformulated opinion testimony from a physician who had no prior connection with the patient in question and who is unwilling to serve as an expert. He insists the creation of expert testimony for a litigant has always been a matter of contractual relations between the parties. Consequently, he urges that the voluntary nature of this relationship should not be overridden by a court except where a party has established that no other reasonable alternative is available. Finally, to the plaintiff, the issue is not one of testimonial privilege but whether he has a duty to testify in this [240]*240particular case. Since opinion testimony normally is available from more than one source, the question is whether Dr. Mason should become a witness at all, not whether he is privileged from disclosing certain relevant information. With these views in mind, we turn to the authorities relied on by the parties.
The cases concerning the compulsion of expert testimony vary greatly depending on the factual situations presented and the legal approach taken. See collection of cases contained in Annot., 77 A.L.R.2d 1182 (1961); Compelling Experts to Testify: A Proposal, 44 U.Chi.L.Rev. 851, 854-55 n. 11 (1977) and cases cited therein. Additionally, secondary authorities disagree about the resolution of this issue. For instance, the Comment to 77 A.L.R.2d 1182 states that the weight of authority holds that, while a court cannot require an unwilling expert to engage in any out-of-court preparation or investigation, it does have the power to compel an expert to state whatever opinions he may have previously formed. On the other hand, it is indicated elsewhere that while an expert may be compelled to testify as to matters within his personal knowledge, he may not be compelled by a private litigant to testify as an expert, this being a matter of contract or bargain. 97 C.J.S. Witnesses § 16(b) (1957).
Plaintiff points out that four jurisdictions have adopted a broad rule that experts cannot be compelled to give testimony based solely on their expertise. People ex rel. Kraushaar Bros. & Co., Inc. v. Thorpe, 296 N.Y. 223, 225, 72 N.E.2d 165, 165-66 (Ct. of Appeals 1947) (an expert who previously had appraised the property in \question could be compelled to testify to his observations of property but not to his opinions); Commonwealth v. Vitello, 367 Mass. 224, 235, 327 N.E.2d 819, 827 (1975) (although opinion testimony about the value of voice-print .evidence would be relevant, a party may not compel the involuntary testimony of an expert solely for his expertise and in the absence of any personal knowledge by the expert of the facts); Braverman v. Braverman, 21 N.J.Super. 367, 368, 91 A.2d 226, 227 (1952) (an expert can be required to testify as to facts no matter how his knowledge of them was obtained but he cannot be compelled to give expert testimony unless he voluntarily contracts to do so); Pennsylvania Co. for Insur. v. City of Philadelphia, 262 Pa. 439, 442, 105 A. 630 (1918) (an unwilling expert cannot be compelled to testify at the request of a private litigant because that is a matter of bargaining and private agreement). See also Agnew v. Parks, 172 Cal.App.2d 756, 764, 343 P.2d 118, 123 (1959) (absent a pre-existing contractual duty to treat or examine a patient, a doctor has no duty to enter an agreement to render services as a medical expert).
Mitchell relies heavily on two federal cases to support her claim for compulsion. Both of these cases, however, are factually distinct from the situation presented for our decision.
In Kaufman v. Edelstein, 539 F.2d 811 (2d Cir.1976), the second circuit held that the trial court did not abuse its discretion in allowing the government in its antitrust action against IBM to compel testimony from two individuals with considerable expertise in the computer industry. Specifically, the government wanted these witnesses “to explain the nature of their duties as computer systems consultants and especially to recount advice they gave to various users and potential users of computer systems.” Id. at 813. Significantly, the government was not asking for an expert evaluation of their evidence in the IBM case but instead stated that the witness’s testimony would be confined to events which occurred between 1960-72. Id. As Judge Gurfein noted in his concurrence, these experts differed from the ordinary expert who has no personal relationship with the subject matter of the litigation. Indeed, they were intimately involved as observers of and participants in the growth and development of the electronic data processing market. Id. at 823. Finally, even the author of the majority opinion indicated that a substantial part of the testimony sought by the government could only be given by these particular experts. Id. at 821. Unlike the present case, most of the testimony [241]*241sought in the Kaufman case was factual rather than opinion. Moreover, these particular experts possessed unique information unavailable from any other source.
The other case relied on by Mitchell to support expert compulsion here is Wright v. Jeep Corporation, 547 F.Supp. 871 (E.D.Mich.1982). In Wright the defendant in a personal injury action, Jeep Corporation, sought discovery of a crash vehicle researcher who had published an adverse report on the safety of certain vehicles manufactured by the defendant. The information sought by Jeep was all research data and memoranda pertaining to a study of highway safety in which the researcher participated and out of which grew the adverse report. Id. at 873. Jeep was interested in learning the factual basis underlying the researcher’s conclusion about its vehicle because it felt the study might be used against it at trial. Id. Although the researcher objected to discovery on the basis that, inter alia, he was an expert and could not be compelled to testify, the court held otherwise. In so ruling, the court noted the researcher was not being required to assist in explaining technical matters but rather was being required to disclose the underlying factual basis for his conclusions so the parties and the court could judge the validity of these conclusions. Id. at 874.
As was the case in Kaufman, the particular information sought from the Wright expert was not readily available from other sources. Moreover, while the factual observations sought in discovery may have involved some expertise and experience, neither the court nor the litigant in Wright were seeking an expert opinion per se from the researcher.
Thus, although both the Wright and Kaufman cases affirm the general principle that an unwilling expert is not immune from compulsory process merely because he is an expert, they do not support Mitchell’s contention that a party has an unlimited right to compel the expert of his choice to provide opinion testimony. Quite the contrary, the decisions in these cases were based, in large part, on the peculiar need of the compelling party for the information sought and its unavailability from other sources.
Although we have not addressed the question of compulsory extraction of expert testimony from an unwilling witness not acquainted with the facts either in discovery or in trial situations, this court has repeatedly stated that our discovery rules should be liberally construed to effectuate disclosure of all relevant and material information to the parties. Pollock v. Deere and Co., 282 N.W.2d 735, 738 (Iowa 1979); Wheatley v. Heideman, 251 Iowa 695, 702, 102 N.W.2d 343, 348 (1960); Hot Spot Detector, Inc. v. Rolfes Electronics Corp., 251 Iowa 647, 651, 102 N.W.2d 354, 359 (1960). Additionally, we have been reluctant to create new privileges in this past, In re Marriage of Gaumer, 303 N.W.2d 136, 138 (Iowa 1981) or to expansively read existing ones. State v. Farber, 314 N.W.2d 365, 367 (Iowa 1982). We have recognized the principle that the public has a right to every man’s evidence, Winegard v. Oxberger, 258 N.W.2d 847, 850 (Iowa 1977), cert. denied, 436 U.S. 905, 98 S.Ct. 2234, 56 L.Ed.2d 402 (1978). We have also afforded our trial judges wide discretion over the course and conduct of a trial including such issues as the competency of a witness, State v. Whitfield, 315 N.W.2d 753, 755 (Iowa 1982); the number of witnesses on a certain point, Ruby v. Chicago, Milwaukee & St. Paul Ry. Co., 150 Iowa 128, 133, 129 N.W. 817, 819 (1911); the attendance of witnesses at State expense, State v. Mayhew, 170 N.W.2d 608, 612 (Iowa 1969); and the witnesses’ court attendance, Hahn v. State, 306 N.W.2d 764, 767 (Iowa 1981). Whether this discretion extends to excusing experts, who are strangers to the litigation, is the issue we must decide.
Plaintiff claims that the absolute right to testimony rule should be rejected because: (1) the expert’s knowledge is a form of intellectual property with considerable economic value; (2) even with compensation it is unfair to take the expert’s opinion involuntarily since he should be allowed freedom of choice regarding the best use of his time [242]*242and, further, has the right to select the recipient, if any, of his labor and service; and (3) public interest requires he devote his energy and talent to his surgical teaching and administrative duties at the University Hospital rather than in private litigation. We conclude that none of these reasons would necessarily preclude his testimony, although they may be legitimate considerations when a trial court is ruling on a motion for expert compulsion.
We do not choose to follow the approach of New York and other jurisdictions which totally excuse an unwilling expert without factual knowledge from testifying. The duty to testify or, alternatively, the “public’s right to everyman’s evidence” arises from the need of our judicial system to have access to all relevant information in ascertaining the truth. 8 J. Wigmore, Evidence § 2192 at 72-73 (McNaughten Rev. 1961). See also United States v. Nixon, 418 U.S. 683, 709, 94 S.Ct. 3090, 3108, 41 L.Ed.2d 1039, 1064 (1974). Although the duty to testify requires sacrifices from a citizen, the inconvenience to the witness may be overborne by the need of the court and litigant for the testimony.
On the other hand, neither do we believe that a litigant, in this instance, should have an unlimited power to compel expert testimony. In contrast to factual witnesses who possess knowledge which is unique and many times irreplacable, expert testimony is not based on any singular personal knowledge of the disputed events. Rather, it depends upon specialized training or other acquired knowledge which allows the expert to draw inferences and form conclusions. Since in most areas of expertise, many individuals possess the necessary qualifications to render expert opinions, this kind of testimony is usually duplicable. Consequently, unlike factual testimony, expert testimony is not unique and a litigant will not be usually deprived of critical evidence if he cannot have the expert of his choice.
The distinctive character of opinion testimony and the ability to obtain it from other sources has important implications for the common law principle of “the public’s right to everyman’s.” Since necessity is the lodestar of this maxim, it may not be applicable to a particular expert, in the absence of some demonstrated need for his opinion.
Moreover, without judicial protection, numerous individuals would be subject to the demands of litigants. In a technical society, many individuals possess some expertise. Additionally, most claims would benefit from learned and expert illumination. Theoretically, parties, regardless of the size of their claim or its potential merit, could routinely issue subpoenas compelling expert discovery. Parties could engage in fishing expeditions, deposing several experts, in an effort to find one favorable to their cause. Although many of these concerns may be exaggerated, the potential for abuse if a party has an unlimited right to compel expert discovery is very real.
We prefer to take a middle ground between total excuse and unlimited compulsion of expert opinions from a stranger to the litigation. We deem that generally an expert witness, absent some other connection with litigation, is free to decide whether or not he wishes to provide opinion testimony for a party.
This is not to say compulsion is never proper. Rather, the distinction between previously formed opinions and those requiring preparation does not serve as a sufficient justification for the abrogation of an expert’s right to freely contract for his services. Conversely, the principle of necessity does provide a sound basis for compulsion of an unwilling expert’s testimony. Consequently, before the court compels an expert to testify solely on the basis of his expertise and in the absence of any other connection to the litigation, the compelling party should affirmatively demonstrate some compelling necessity for an expert’s testimony that overcomes the expert’s and the public’s need for protection. Additionally, an adequate plan of compensation must be presented. Finally, an expert only can be compelled to give previously formed [243]*243opinions and can not be required to engage in any out-of-court preparation.
If, after balancing the relative rights of the expert and the needs of the litigants, necessity is established, then the fair and just administration of our judicial system would override any concerns about forcibly extracting a prior opinion from an expert. In cases of necessity, a duty would arise on the part of the expert to provide opinion testimony. Such a duty would run not to the compelling party but to society and its need for all relevant information in ascertaining the truth. 8 Wigmore § 2192 at 72-73. Conversely, in the absence of such showing, a particular expert has no duty to provide opinion testimony.
Thus, we conclude our trial courts have wide discretion to quash subpoenas or issue protective orders whenever a litigant’s demand for a particular expert constitutes an unnecessary or unwarranted intrusion. Conversely, the trial court has the power to compel an unwilling expert to provide pre-formulated opinion testimony whenever a litigant establishes a compelling need for the testimony.
At this time, we do not choose to establish specific standards for the trial bench to utilize when confronted with this issue. We not only cannot foresee all of the problems that may arise, but we are also aware of the ingenuity of litigants and counsel to adapt and use guidelines to their advantage in a manner that would result in a rigid rather than a flexible approach to the resolution of this problem. Our trial courts are in a better position to balance the rights of the witness and any unfairness that may result from expert compulsion against the need of the court and litigant for the testimony. We deem it better to grant them discretion to consider a variety of factors and their appropriateness to or importance in deciding each individual case.
Here, the trial court determined it could not excuse the witness from testifying but could restrict the scope of the inquiry. Consequently, the court did not exercise discretion in deciding whether Dr. Mason should be required to give expert opinion testimony. We hold this was error.
We find it unnecessary to remand this matter for a ruling, however. Mitchell did not present any evidence by affidavit or otherwise supporting her motion for compulsion of Dr. Mason’s expert opinion. Dr. Mason’s affidavit that other physicians in the state are qualified to render expert opinion in the medical malpractice action is unrefuted. Since Mitchell did not affirmatively demonstrate a compelling necessity for this particular witness’s expert testimony, the trial court erred in granting her application. Consequently, we remand for entry of an order denying Mitchell’s application.
In the limited circumstances of this case, we find sufficient grounds for sustaining the writ of certiorari.
WRIT SUSTAINED.
All Justices concur except LARSON and McGIVERIN, JJ., who dissent.