delivered the opinion of the court:
This case concerns the quantum and quality of evidentiary proof necessary to maintain medical malpractice actions based on res ipsa loquitur and negligence. In 1972, plaintiff Judith Marie Spidle underwent a supra-cervical hysterectomy after recurrent attacks of pelvic inflammatory disease. Dr. Lee A. Steward had treated Mrs. Spidle during these attacks and was her surgeon during the operation. Following the operation, she developed vaginal fecal fistula and a drainage sinus at the lower part of the surgical incision, indicating a communication between the vagina, colon and abdominal wall. This caused fecal matter to drain from her incision and from her vagina. *5Although the abdominal incision was closed relatively soon thereafter, the vaginal fecal fistula persisted for approximately two years before surgically corrected by another doctor. Mrs. Spidle, however, has continued to experience medical difficulties. There was evidence that Dr. Steward’s initial surgery caused the fistula. Spidle v. Steward (1979), 68 Ill. App. 3d 134, 135.
Mrs. Spidle and her husband, Ada Spidle, timely filed a medical malpractice suit in Coles County against Dr. Steward, another doctor, and the hospital in which Mrs. Spidle was treated, asking damages for personal injuries, medical expenses for problems related to the surgery, and for Spidle’s loss of consortium. The suits against the other doctor and the hospital were settled prior to jury deliberations. At the close of plaintiffs’ case, the trial court directed a verdict for Dr. Steward (hereinafter referred to as defendant) on the two complaint counts based upon res ipsa loquitur, and, at the end of the trial, the court refused to give plaintiffs’ modified version of Illinois Pattern Jury Instruction, Civil, No. 105.01 (2d ed. 1971). The jury found for the defendant on the two counts alleging negligence.
The Fourth District Appellate Court affirmed the trial court, one judge dissenting on the res ipsa loquitur issue. (68 Ill. App. 3d 134.) We granted leave to appeal. We reverse as to res ipsa loquitur and affirm as to the jury instruction.
The res ipsa loquitur doctrine is a species of circumstantial evidence permitting the trier of fact to draw an inference of negligence if plaintiff demonstrates that he or she was injured “(1) in an occurrence that ordinarily does not happen in the absence of negligence, (2) by an agency or instrumentality within the defendant’s exclusive control, and (3) under circumstances indicating that the injury was not due to any voluntary act or neglect on the part of the plaintiff ***.” (3 J. Dooley, Modern *6Tort Law sec. 48.02 (1977). See also W. Prosser, Torts sec. 39 (4th ed. 1971)). Illinois recognizes this doctrine (Metz v. Central Illinois Electric & Gas Co. (1965), 32 Ill. 2d 446) and its applicability to medical malpractice actions (Edgar County Bank & Trust Co. v. Paris Hospital, Inc. (1974), 57 Ill. 2d 298; Walker v. Rumer (1978), 72 Ill. 2d 495).
Before our opinion in Walker, there was a misconception that res ipsa loquitur only applied in medical malpractice actions when the medical activity at issue was within the common knowledge of laymen. (See, e.g., Slater v. Missionary Sisters of the Sacred Heart, (1974), 20 Ill. App. 3d 464; Estell v. Barringer (1972), 3 Ill. App. 3d 455.) The court recognized in Walker, however, that expert testimony could establish a negligence probability where jurors were unfamiliar with the issue. (72 Ill. 2d 495, 499-500.) Our opinion in Edgar County Bank & Trust Co. v. Paris Hospital, Inc. (1974), 57 Ill. 2d 298, noted that one purpose of res ipsa loquitur was to insure that relevant evidence was produced at trial. In addition, the doctrine is useful in combatting the reluctance of medical personnel to testify against one another. (Sanders v. Frost (1969), 112 Ill. App. 2d 234, 241; Prosser, Torts sec. 39, at 227 (4th ed. 1971).) Doctors, for example, “may be more willing to testify that the injury was of a kind which would not ordinarily occur in the exercise of due care than they would be to specify those acts which constituted negligence.” Note, The Application of Res Ipsa Loquitur in Medical Malpractice Cases, 60 Nw. U.L. Rev. 852, 865 (1966).
In accordance with the foregoing principles, we decided in Walker that res ipsa loquitur could be an appropriate theory of liability in medical malpractice cases. Since that issue was decided on the pleadings, we did not consider the quantity of evidence required to prove the elements of res ipsa loquitur. Nor did we discuss the *7standard by which the trial court determines, as a matter of law, the amount of evidence necessary to present a res ipsa loquitur theory to the jury. These issues are presented now.
The trial court must in the first instance decide whether, as a matter of law, the res ipsa loquitur doctrine applies at all. (Drewick v. Interstate Terminals, Inc. (1969), 42 Ill. 2d 345, 349.) It will not apply unless a duty of care is owed by the defendant to the plaintiff. (See, e.g., Hunter v. Alfina (1969), 112 Ill. App. 2d 432.) Assuming that a duty of care exists, and in this case the issue is beyond doubt, the trial court must also determine, as a matter of law, (1) whether plaintiff’s pleaded facts would ever establish the three elements of control, lack of contributory negligence and the improbability of injury without negligence, and (2) whether those elements, as pleaded, gave sufficient notice to the defendant of the res ipsa loquitur cause of action. See, e.g., Kruger v. Newkirk (1976), 40 Ill. App. 3d 581.
On a motion for directed verdict, the role of the trial judge is to view all of the evidence in a light most favorable to the nonmovant and decide whether a verdict for the nonmovant could ever stand. (Pedrick v. Peoria & Eastern R.R. Co. (1967), 37 Ill. 2d 494, 510.) In Cox v. Yellow Cab Co. (1975), 61 Ill. 2d 416, 421, for example, this court held the doctrine inapplicable as a matter of law because the evidence introduced by the plaintiff clearly established that the defendant did not have control over the instrumentality causing the injury. (See also Krotke v. Chicago, Rock Island & Pacific R.R. Co. (1974), 26 Ill. App. 3d 493, 501-02; Wimberley v. Material Service Corp. (1973), 12 Ill. App. 3d 1051; Collgood, Inc. v. Sands Drug Co. (1972), 5 Ill. App. 3d 910; 3 J. Dooley, Modern Tort Law sec. 48.21 (1977).) In the instant case, since the parties agree that Mrs. Spidle was injured while under control of the defendant *8and was without contributory negligence, the only issue presented is whether the plaintiffs have introduced enough evidence that the injury would not have happened, ordinarily, without negligence.
Defendant contends that no evidence submitted by plaintiffs was sufficient to support this case going to the jury on the res ipsa loquitur counts. Plaintiffs’ expert witness, Dr. Thomas Wilson, answered these questions about the probability of negligence:
“Q. Is a hysterectomy, supracervical hysterectomy, removal of the tubes and ovaries, a type of surgery which in ordinary course, is likely to lead and have as one of its results, now, in the ordinary course, mind you, in the ordinary course, likely to lead to and have as one of its results, in the absence of any negligence, the formation of fecal vaginal fistulas?
A. This is a rare and unusual complication of hysterectomies.
Q. It is not one one would normally expect, is it?
A. No.”
Defendants argue that the doctor’s answer only concerned unusual results, not unusual results ordinarily or most often due to negligence. As such, the defendant contends that, even in a light most favorable to plaintiffs, res ipsa loquitur cannot be invoked. While we agree with the defendant and the appellate court that surgeons are not liable merely for unusual, unfortunate results, we think that these answers, combined with other testimony, were sufficient under Pedrick to present a jury question regarding the probability of negligence.
Plaintiffs’ counsel asked, in his first question, whether the fistula would, in the absence of negligence, ordinarily result. If the expert had answered that question “no,” he would have established directly plaintiffs’ initial burden with respect to the probability component of res ipsa loquitur. With such an answer, he would have testified, in effect, that supracervical hysterectomies resulting in *9fistulas more probably than not have negligent antecedents. Such a direct answer, contrary to the conclusions of the appellate court in Grubb v. Jurgens (1978), 58 Ill. App. 3d 163, would be sufficient initially even though it would not have constituted proof that fistulas never happen without negligence. To hold otherwise, to require a plaintiff to conclusively prove negligence, would “obviate the purposes and policy behind shifting the burden of coming forward with the evidence to the defendant” (Spidle v. Steward (1979), 68 Ill. App. 3d 134, 140 (Craven, J., dissenting)), a policy this court endorsed in Edgar County Bank & Trust Co. v. Paris Hospital, Inc. (1974), 57 Ill. 2d 298. Most courts have agreed with this view and have required plaintiff to show only that the result “ordinarily,” not always, had negligent antecedents. Walker v. Rumer (1978), 72 Ill. 2d 495; Edgar County Bank & Trust Co. v. Paris Hospital, Inc. (1974), 57 Ill. 2d 298; Metz v. Central Illinois Electric & Gas Co. (1965), 32 Ill. 2d 446; People v. Morris (1978), 60 Ill. App. 3d 1003; Jirik v. General Mills, Inc. (1969), 112 Ill. App. 2d 111; Summers v. Northern Illinois Gas Co. (1969), 117 Ill. App. 2d 125, 138; 2 Restatement (Second) of Torts sec. 328D and comments (1965).
Unfortunately, the expert in this case answered the question indirectly. We cannot conclude with equanimity, from this colloquy alone, whether he meant fistula formation after hysterectomies is usually á result of negligence or whether there is an equal probability that they occur despite the exercise of due care. In this case, however, the expert also testified about the inadvisability of operating on Mrs. Spidle if her pelvic inflammatory disease was in an acute or an acute flare-up stage. The defendant even agreed with the plaintiffs’ expert regarding the inadvisability of operating during an acute stage, although denying that Mrs. Spidle was in such a stage. Evidence was introduced, however, that Mrs. Spidle was in an acute stage *10and that the defendant, after the operation, admitted he “operated a little too soon.” In a light most favorable to plaintiffs, a reasonable person could conclude that plaintiffs’ expert believed that this fistula, more probably than not, resulted from defendant’s negligence. If believed, this is evidence of more than a mere unusual occurrence (see Hahn v. Illinois Office Equipment Co. (1976), 42 Ill. App. 3d 29, 31), from which the jury could have inferred negligence under res ipsa loquitur.
To be sure, some of the foregoing evidence was controverted. Nevertheless, factual disputes presenting credibility questions or requiring evidence to be weighed should not be decided by the trial judge as a matter of law. As was stated in Pedrick: “Clearly, the constitution does, and judges should, carefully preserve the right of the parties to have a substantial factual dispute resolved by the jury, for it is here that assessment of the credibility of witnesses may well prove decisive.” (Pedrick v. Peoria & Eastern R.R. Co. (1967), 37 Ill. 2d 494, 504; see also Lovejoy v. National Food Stores, Inc. (1973), 12 Ill. App. 3d 982; Wolfe v. Whipple (1969), 112 Ill. App. 2d 255; Summers v. Northern Illinois Gas Co. (1969), 117 Ill. App. 2d 125, 138; Traylor v. The Fair (1968), 101 Ill. App. 2d 268, 275.) This right was not preserved in the instant case.
Drewick v. Interstate Terminals, Inc. (1969), 42 Ill. 2d 345, illustrates the preferred approach. There a steel ventilator-window sash fell from a building owned by defendants and struck the plaintiff. It was agreed that plaintiff was not contributorially negligent and that this type of accident would not ordinarily happen without negligence. But whether defendant exercised control over the window was disputed. The court examined the record as a whole and held “it was not error for the trial court to send the case to the jury on a res ipsa instruction, particularly where the jury was *11expressly instructed that control on defendant’s part was a prerequisite to its liability.” (42 Ill. 2d 345, 351.) We see no reason to treat the probability component of res ipsa loquitur differently from the control component. Plaintiffs have the burden of proof on each element of res ipsa loquitur. And we think that from this record, read as a whole, a jury could have decided that each of these elements was proved. Therefore, the res ipsa loquitur negligence counts should have been submitted to the jury for a decision.
The Illinois civil pattern jury instruction on res ipsa loquitur states in pertinent part:
“The plaintiff has the burden of proving each of the following propositions:
[the requirements of injury, control, lack of contributory negligence and probability of injury]
If you find that each of these propositions has been proved, the law permits you to infer from them that the defendant was negligent ***.” IPI Civil No. 22.01 (2d ed. 1971).
With this instruction, we think the jury is fully capable of determining these issues in accordance with the law.
The California Supreme Court reached similar conclusions in Clark v. Gibbons (1967), 66 Cal. 2d 399, 412, 426 P.2d 525, 534, 58 Cal. Rptr. 125, 134. In that case, an expert testified to a low incidence of injuries when due care was used. Other evidence tended to establish specific acts of negligence. The court reasoned that this evidence, combined, presented a jury question under res ipsa loquitur. Subsequent cases have struck res ipsa loquitur counts where expert testimony of a rare and unusual result was not accompanied by further evidence of negligent acts that could have caused the injury at issue. (See, e.g., Contreras v. St. Luke’s Hospital (1978), 78 Cal. App. 3d 919, 933, 144 Cal. Rptr. 647, 656.) When the trial judge in the instant case permitted the ordinary negligence counts to go to the jury, he ruled that a verdict *12finding the defendant liable could stand. The evidence sufficient to hold defendant liable under negligence specifically does not eliminate the res ipsa loquitur doctrine; rather, the foundation for it and the inference of negligence permitted under it were strengthened (Prosser, Torts sec. 40, at 231-32 (4th ed. 1971)), at least to the extent of presenting a jury question.
The second indication of the soundness of our reasoning lies in the statements made by the trial judge in striking the res ipsa loquitur counts. He said:
“Illinois, regardless of what any of us say, still gives expression to the, as far as res ipsa is concerned, to what we call the gross negligence or common negligence rule.”
He cited Comte v. O’Neil (1970), 125 Ill. App. 2d 450, and Estell v. Barringer (1972), 3 Ill. App. 3d 455, as support for his position, and then noted that our decision in Edgar County Bank & Trust Co. v. Paris Hospital, Inc. (1974), 57 Ill. 2d 298, criticized these prior holdings:
“They merely said basically, the evidence merely created an inference of negligence under res ipsa, and that is as far as they went. Even in referring to the intramuscular injection which was involved in the Edgar County case, I believe Mr. Sunderman correctly stated the law or the opinion of that court. They felt this was a common knowlege type of thing and again, you might say hung their head on that doctrine ***. Looking at the evidence most favorable to the plaintiff, obviously a fistula' did occur after the operation. There is no testimony in the record that it was caused at the time of the operation. Precipitating factors resulting from the operation could have caused or may not have caused it. I don’t know.
***
I don’t think it is a res ipsa case under any stretch of the imagination, based on the law as it exists in Illinois now.”
From these statements it is apparent that the trial judge relied on cases rendered inapplicable by the opinion in Edgar County. At the time of this trial, other attorneys, *13like the defendant in Walker, similarly misinterpreted that opinion. We must remain consistent with Walker and Edgar County nevertheless. We conclude, therefore, that from all of the evidence, viewed in a light most favorable to plaintiffs, a jury could have determined that the foundation for the res ipsa loquitur doctrine was laid and, further, could have concluded that the defendant was negligent. Since this jury’s conclusions on this issue will never be known, we must remand the case for a new trial on the res ipsa loquitur counts.
At the end of the trial, plaintiff tendered the following jury instruction, a modified version of IPI Civil No. 105.01 (2d ed. 1971) relevant to the causes of action based upon negligence:
“In treating and operating upon a patient, a doctor must possess and apply the knowledge and use the skill and care that is ordinarily used by reasonably well-qualified doctors in the locality in which he practices or in similar localities in similar cases and circumstances. A failure to do so is a form of negligence that is called malpractice.
The only way you may decide the standard of care that is required in the circumstances is by a doctor called as an expert witness. You must not attempt to determine this standard from any personal knowledge you may have.”
The tendered instruction differs from IPI Civil No. 105.01 in that the second paragraph of No. 105.01 states that expert witnesses must also establish defendant’s deviation from the standard of care. The trial court upheld defendant’s objection to this instruction, neither plaintiff nor defendant tendered IPI Civil No. 105.01, and, consequently, no instruction concerning the standard of care or deviation from that standard was given.
Even adopting the view argued by the plaintiffs, their modified version of IPI Civil No. 105.01 was inadequate because it contained no instruction about the necessity of establishing a deviation from the standard of care. Accord*14ing to cases cited by the plaintiffs and others reviewed by us, establishing a deviation from the standard of care is the second essential element in a negligence cause of action. (Walski v. Tiesenga (1978), 72 Ill. 2d 249.) Because plaintiffs’ proffered instruction omitted mention of this element, it was properly refused.
The judgment of the appellate court is affirmed as to its affirmance of the verdict on the negligence counts and reversed as to its affirmance of the dismissal of the res ipsa loquitur portions of the complaint. The judgment of the circuit court of Coles County is affirmed as to the negligence counts and reversed as to its dismissal of those portions of plaintiffs’ complaint based on res ipsa loquitur. The cause is remanded to the circuit court for further proceedings consistent with this opinion.
Appellate court affirmed in part and reversed in part; circuit court affirmed in part and reversed in part; cause remanded.