BAZELON, Chief Judge:
Appellant was convicted by a jury of rape, robbery, and assault with a deadly weapon. His major defense was insanity. On appeal, he contends that the trial judge should have entered a judgment of acquittal by reason of insanity.
I
This court has always been reluctant to order such judgments of acquittal.1 Our reluctance is rooted in the nature of the jury’s role in insanity cases. In the early eighteenth century, the test for criminal responsibility was whether the accused “does not know what he is doing, no more than * * * a wild beast.”2 Under this test, the jury did not need to hear and evaluate a complex body of evidence. Presumably the jury and the witnesses knew a wild beast when they saw one. Later, English courts began to focus on whether the accused could distinguish between right and wrong. They also began to hear medical testimony.3 The landmark M’Naghten case4 made both these trends a standard part of English and American law. Under M’Naghten, the test for insanity was whether the accused was “laboring under such a defect of reason, from disease of the mind, as not to know the nature and quality of what he was doing, or if he did know it, that he did not know he was doing what was wrong.”5 The use of the term “disease of the mind” was significant since it firmly established the relevance [446]*446of medical testimony. The jury now had a broader role — to evaluate medical testimony in light of the right-wrong criterion. Soon, however, doctors began to complain that the right-wrong test permitted too narrow an inquiry into the accused’s mental condition, that it precluded doctors from presenting important medical data.6 In Durham v. United States,7 we announced a new test for insanity: “An accused is not criminally responsible if his unlawful act was the product of a mental disease or defect.”8 We intended to widen the range of expert testimony in order to enable the jury “to consider all information advanced by relevant scientific disciplines.” 9
This purpose was not fully achieved, largely because many people thought Durham, was only an attempt to identify a clearly defined category of persons— those classified as mentally ill by the medical profession — and excuse them from criminal responsibility. In fact, the medical profession has no such clearly defined category, and the classifications it has developed for purposes of treatment, commitment, etc., may be inappropriate for assessing responsibility in criminal cases. Since these classifications were familiar, however, many psychiatrists understandably used them in court despite their unsuitability. And some psychiatrists, perhaps unwittingly, permitted their own notions about blame to determine whether the term mental illness should be limited to psychoses, should include serious behavior disorders, or should include virtually all mental abnormalities. To ensure that the views of the experts would not bind the fact-finder, we decided to give mental illness a legal definition independent of its medical meaning. We announced in McDonald v. United States that mental illness “includes any abnormal condition of the mind which substantially affects mental or emotional processes and which substantially impairs behavior control.” 10 We recognized that there may be many reasons why a person’s ability to control is impaired. His mental or emotional processes may have been adversely affected by his genetic structure, his physical condition, his family, educational or cultural backgrounds.11 Thus we called upon the jury to “consider testimony concerning the development, adaptation and functioning of these processes and controls.”12
In insanity cases today, the jury must be prepared to hear evidence concerning diverse aspects of defendant’s life and then to make difficult judgments regarding the impairment of behavioral processes and controls. By their very nature these judgments cannot be precise. Thus, within the confines of the Durham-McDonald standard, the jury must be allowed a wide latitude in its task. A judgment of acquittal by reason of insanity is appropriate only when a jury verdict of guilty would clearly violate the law or the facts.
We cannot say that this was the situation in Washington’s case. The district court did not err in its refusal to enter a judgment of acquittal by reason of insanity.
II
We all agree that this court’s limited role in supervising the verdict does not [447]*447imply an equally limited role in supervising the evidence which is put before the jury. To the contrary, the jury’s wide latitude in deciding the issue of responsibility requires that trial judges and appellate judges ensure that the jury base its decision on the behavioral data which are relevant to a determination of blameworthiness.13 We disagree, however, on the quality of the data in this ease. Judge Robinson and I are deeply troubled by the persistent use of labels and by the paucity of meaningful information presented to the jury. Experience with the administration of the insanity defense has revealed that, despite the earnest efforts of witnesses, counsel and judges, these defects are a recurring problem. We will therefore describe them in detail in this section. Judge Fahy will state his views on this matter in a separate concurring opinion.
The testimony of the defense psychiatrist, Dr. Adland, was based solely on a one hour and fifteen minute interview with defendant. Dr. Adland did not administer electroencephalogram, neurological, or physical tests, and did not have the benefit of reports of the tests given at Saint Elizabeths Hospital. He requested permission to see them, but permission was denied.
Since the defendant was at Saint Elizabeths Hospital for two months, the two Government psychiatrists had an opportunity for more prolonged observation. Yet both Dr. Owens and Dr. Ham-man testified that they had seen Washington for approximately the same amount of time as Dr. Adland. Of course, they did have the benefit of the testing and observations performed by others at the Hospital. As Dr. Owens explained:
When a patient is under constant observation, the examinations that were conducted in St. Elizabeth’s by the psychiatrists, laboratory studies, psychological examinations, social service, interviews with relatives, all of this was part of the basis of my opinion that I rendered and the examination which I conducted at the medical staff conference on November 16, 1965. * * * By [constant observation] I mean 24 hours a day, and reports are submitted to the physicians as to their behavior, actions or activity while on the ward.
Unfortunately, except for brief references to a Rorschach test, none of this information was presented to the jury. The Government psychiatrists claimed to have based their conclusions on these studies, but they told the jury only the conclusions without any explanation of the studies themselves, what facts the studies uncovered, and why these facts led to the conclusions.
There was other available information, as well, which the jury was not told about. When Washington was twelve or thirteen, he was committed to Cedar Knolls, the District of Columbia School for Children. Apparently the records of that institution contained a lengthy history of Washington’s childhood. At first, defense counsel moved them into evidence, but later he withdrew that request, perhaps because he thought it would be tactically unwise to make the jury read such a long report. Whatever the reason, the jury was forced to make its decision without any historical background on the defendant.
The omission of significant underlying information was one defect in the testimony. Another was that the jury was often subjected to a confusing mass of abstract philosophical discussion and fruitless disputation between lawyer and witness about legal and psychiatric labels and jargon. Dr. Hamman’s entire testimony on direct examination was that Washington did not have a “passive-aggressive personality,” did not suffer from any “personality trait disturbance,” did not have “an irresistible impulse,” [448]*448was “not mentally ill,” and was not “abnormal from the standpoint of psychiatric illness.” A substantial part of Dr. Owens’ testimony was similar. He was familiar with the defendant, had participated in a staff conference at which the defendant was discussed, and had formed an opinion about him.
Q. All right. And what was that opinion ?
A. It was my opinion that he did not have a mental disease or mental defect. * * *
He testified also that the defendant did not have “an irresistible impulse” to rape, did not have a “passive-aggressive personality,” and that in any event someone with a “passive-aggressive personality” was not necessarily “mentally ill.”
Even if these labels had meaning for the witnesses,14 the testimony was useless unless that meaning was communicated to the jury. Explanation was attempted but it was often more confusing than clarifying. Dr. Owens explained that a “passive-aggressive personality”
is a type of personality that an individual has, that is, everybody has some-type of personality. We all have a type of personality. I mean no one has no personality. We have some type. Well, you may say schizoid personality, or compulsive personality, but speaking of the one that you ask, such [as] the passive aggressive personality, these are broken down into two different categories.
One is passive and one is aggressive. Usually in these people the aggressive type acts out in an aggressive manner, to either major or minor stressful situations, they maneuver under close confinement or under strict rules and regulations except maneuvering into a psychosis.
It is generally considered that the passive type or the aggressive type frequently or sometimes an aggressive personality will also behave in a passive manner.
This is where we get the term “passive-aggressive.” This is more a classification of the type of personality that the individual has.
******
We all have a type of personality. For example, physicians are generally considered to be compulsive personalities. That is, they are very meticulous to details and work things out or in a very orderly and organized fashion.
Generally speaking lawyers are considered to be aggressive or to have an aggressive personality. If they are not, they cannot be real passive [sic] and really do an expert job.
They have to be aggressive. Everybody has a type of personality. I mean, you have to be categorized somewhere.
Other explanations cast serious doubt upon the basis for many of the experts’ conclusions as expressed in their labels. For example, Dr. Owens did not think the defendant had an “impulse to rape.” Here is his explanation: “I think it was not an impulse to rape. It was an impulse to have sexual relations with a lady and if she did not agree with it, why, they forced her.” Dr. Hamman agreed that Washington did not have an irresistible impulse to rape. But here is what “irresistable impulse” meant to Dr. Hamman:
Q. Isn’t this almost irresistible, this antisocial act when he is in this situation with the urge?
A. Not from the way I understand irresistible impulse. An irresistible impulse means to me that there is a conflict and the unwanted behavior breaks through. I do not think there is a conflict in Mr. Washington.
Q. But, without the theory of conflict, without the conflict, isn’t it a fact that he is in the situation with the urge for sexual contact, he cannot stop?
[449]*449A. Well, he will just do it. no desire to stop. He has
Q. He has no power to stop ?
A. That is correct.
Q. And, doctor, isn’t it a fact that he has no power to stop an irresistible impulse ?
A. Not as I understand it.
Q. And you understand it from a legal terminology?
A. I understand it both from legal terminology and from a psychiatric terminology.
Dr. Owens testified also that Washington’s difficulty in controlling his sexual impulses did not affect his “voluntary controls.”
Q. Didn’t this impulse to have sexual relations affect his voluntary behavior controls?
A. No, I would not think so. I think, had a policeman, or witnesses or say, if he and two or three men had been going to rape a lady. and there had been thirty other men present, where their force would not overpower the woman, that they would have backed off for another lady somewhere else to have raped.
I think when I say it impairs his voluntary control, I would say that it did not.
Dr. Hamman thought that Washington was “psychiatrically normal.” Then he added, “The best definition of normal I have ever heard is the person is not too neurotic.”
These labels and definitions were not merely uninformative. Their persistent use served to distract the jury’s attention from the few underlying facts which were mentioned. For example, the fact that Washington’s difficulties “in relating adequately to other people are more severe or more extreme than the average [person’s]” was immersed in a dispute about whether to classify these difficulties as a “personality defect,” a “personality problem,” a “personality disorder,” a “disease,” an “illness,” or simply a “type of personality.”
The psychological examinations suggested a person of “general intellectual ability, with little feelings for others,” a person “who acts out in an antisocial way, has little control over his desires and his needs * * * has little guilt * * * does not feel things are wrong. * * * ” But these facts were obscured by a dispute about whether a person with “soeiopathie symptomology” is or is not “mentally ill.”
Again and again the jury was diverted from evidence of the defendant’s underlying mental and emotional difficulties by the emphasis on eonclusory phrases. After defense counsel vigorously cross-examined Dr. Owens and brought out some facts which indicated that Washington’s mental and emotional processes of control may have been impaired, the prosecuting attorney rehabilitated his witness as follows:
Q. Notwithstanding that history, doctor, and after that thorough study of Mr. Washington, you are of the opinion that he was not suffering with a mental illness on August 9, is that correct?
A.. That is correct.
In this regard Dr. Hamman’s testimony epitomized the whole trial. At times his testimony was more favorable to the defendant than the defense psychiatrist’s testimony. According to Dr. Hamman, Washington had a twelve or thirteen year history of aggressive behavior. He has “very little regard for * * * people. And when he wants something, he takes it.” “He has a tendency to be withdrawn, does not relate to people, tends to stay by himself.” “He act out his impulses.” “Mr. Washington [does not have] much control.” “He is a very aggressive individual.” Dr. Ham-man agreed that Washington “does not have any brakes, things that stop him from doing antisocial acts” and that “he has no power to stop.” But these underlying facts were muddied by disputes and conclusions about medical and legal terminology — about whether a person is “normal” if he is not “too neurotic,” about whether Washington was suffer[450]*450ing from a “neurosis,” about whether he has a “schizoid personality” as opposed to “traits of a schizoid nature,” about whether “he has sociopathic symp-tomology,” or whether instead “he has aggressive antisocial activity,” about whether he was a “sociopath,” had “personality difficulty,” “personality disorder,” or merely “personality problems,” about whether he suffered from “irresistible impulses,” about whether his aggression indicated that he had a “character disorder,” and about whether his aggressive acts were caused by a “personality pattern the way he reacts, rather than [a personality] disorder.”
Whatever opportunity the jury may have had to focus upon the underlying information provided by Dr. Hamman, this opportunity was materially diminished by a series of redirects and recrosses which dealt entirely with labels. The prosecutor asked on redirect examination :
Q. Now, the mere fact that this defendant has somewhat of a weird background according to what has come out here, and a very interesting sexual background, do you feel — I mean, as a result of all of this information you have assembled concerning him, is it still your opinion that this defendant was not suffering with a mental illness on August 9, 1965 ?
A. That is correct. I do not think he was.
The defense attorney responded on recross :
Q. Doctor, he still has this behavior problem and the control problem with these sexual urges, right?
A. I am hesitating because I want to condense this as much as possible. He has problems in society. He does not have a problem with himself, and I think mental illness — it is my opinion that mental illness is one of the problems between he [sic] and himself. He may act it out and he may not. But I do not think he has much problem with himself about this. He takes what he wants.
Q. He is an emotional cripple, is he not?
A. Yes.
******
Q. Doctor, wouldn’t you say, based upon the history that Mr. Washington is chronically ill?
A. No. I do not think he is ill.
Q. You do not think he is ill at all?
A. No.
Q. He just cannot control what he is doing?
A. Well, now, again when you say “can’t,” you imply that he would like to, and has a conflict. I don’t think he wants to.
And finally, on redirect:
Q. * * * The mere fact that he is emotionally crippled, does that mean he is mentally ill?
A. No.
******
Q.- Now, I will ask you this. You have been asked, or in reply to a question you indicated that this defendant will take what he wants.
A. Yes.
Q. Well, now, the mere fact that he will take what he wants even if it is in the field of sex, does that mean he is mentally ill?
A. No.15
It seems clear to Judge Robinson and me that the persistent use of conclusory labels may have hindered the jury in getting to the underlying facts.__But~w.e_ tbinlr fhat the jury obtained enough concrete information to preclude usJxom disturbing the verdict. The defense psychiatrist and, on pross-fixaiwnatwn.J-.he Government psychiatrists gave some meaningful descriptions of ripfondafft’s mental and emotional processes as emphasized iir" Judge b'ihy’s concurring opinion herein. Moreover, we recognize that, taken as a whole, the testimony in [451]*451this case was, if anything, a little better than that in most insanity cases. Under these circumstances, reversal seems inappropriate. We conclude, therefore, that the conviction should be affirmed.
Ill
We all agree that more effort is needed in future cases to ensure that the issue of responsibility is decided upon sufficient information. Unfortunately, we have no easy solution. The history of the insanity defense in this jurisdiction shows that the misuse of conclusory labels has always been a central concern. The M’Naghten test, which we have quote above,16 had two major defects. First, it encouraged psychiatrists to say whether the defendant knew “right” from “wrong.” terms which have -no particular mpriiV.p] mpgnjqjr Consequently, because the psychiatrist’s attention was focused on these judgments and not on the medical facts, the jury was diverted from and perhaps even deprived of his expert knowledge. Second, and perhaps more important, the right-wrong test required psychiatrists to make a moral judgment about the defendant. It has often been argued that in the guise of an expert, the psychiatrist became the thirteenth juror, and unfortunately the most important one.17 Thus, the labels of “right and wrong” precluded the jury from considering all the relevant information and also encouraged the psychiatrist to impose his moral judgment upon the jury.18
In Part I we described the steps taken in Durham and McDonald to enable the jury to consider all the relevant information about the defendant. Durham and McDonald were also attempts to clarify the respective roles of the expert19 and the jury by reducing the emphasis on conclusory labels. We thought the new test announced in Durham would allow the expert to testify in medical terms familiar to him and to his profession. The jury would no longer be forced to focus on the conclusory labels used by the expert.
Soon after Durham we found that, although the jury was being given more information, still too much emphasis was being placed upon the labels used by the psychiatrist, upon whether he concluded that the defendant did or did not have a “mental illness.” In Carter v. United States20 we pointed out again that Durham was designed to eliminate this kind of labeling.
Unexplained medical labels — schizophrenia, paranoia, psychosis, neurosis, psychopathy — are not enough. Description and explanation of the origin, development and manifestations of the alleged disease are the chief functions of the expert witness. The chief value of an expert’s testimony in this field, as in all other fields, rests .upon the material from which his oninion is fashioned and tne reasoning by which he progresses from nis material — to—his—coirdu&Tuiu—in—tfe» explanation ox file disease and its dynamics, that is, how it occurred, developed, and affected the mental and emotional processes of the defendant; it does not lie in his mere expression of conclusion. * * * Durham was intended to restrict to their proper medical function the part played by the medical experts.21
This warning was not effective enough, so in McDonald v. United [452]*452States22 we gave the terms “disease” and “defect" a legal definition independent tiftneir medical meanings.
Our eight-year experience under Durham suggests a judicial definition, however broad and general, of what is included in the terms “disease” and “defect.” In Durham, rather than define either term we simply sought to distinguish disease from defect. Our purpose now is to make it very clear that neither the court nor the jury is bound by ad hoc definitions or conclusions as to what experts state is a disease or defect. What psychiatrists may consider a “mental disease or defect” for clinical purposes, where their concern is treatment, may or may not be the same as mental disease or defect for the jury’s purpose in determining criminal responsibility. Consequently, for that purpose the jury should be told that a mental disease or defect includes any abnormal condition of the mind which substantially affects mental or emotional processes and substantially impairs behavior controls. Thus the jury would consider testimony concerning the development, adaptation and functioning of these processes and controls.
We emphasize that, since the question of whether the defendant has a disease or defect is ultimately for the triers of fact, obviously its resolution cannot be controlled by expert opinion. The jury must determine for itself, from all the testimony, lay and expert, whether the nature and degree of the disability are sufficient to establish a mental disease or defect as we have now defined those terms. What we have said, however, should in no way be construed to limit the latitude of expert testimony.23
We clearly separated the legal and moral question of culpability from the medical-clinical concept of illness. We hoped thereby to separate the roles of the psychiatrist and the jury, with the former stating medical-clinical facts and opinions and the latter making the judgments required by the legal and moral standard.24 Also, we hoped that the expert’s conclusion would not be so heavily weighted in the jury’s minds if we made plain that the expert and the jury had different judgments to make.
Even after McDonald, though, we allowed the experts to state whether they thought the defendant had a mental disease or defect. We assumed that the expert could separate the medical judgments which he was supposed to make from the legal and moral judgments which he was not supposed to make. .It [453]*453has become abundantly apparent that this theory has not worked out. Too often conclusory labels — both medical and legal — have substituted, albeit unwittingly, for the facts and analysis which underlie them.25 The transcript in this case illustrates that they may have served more to confuse the jury than to guide it. Also, testimony in terms of “mental disease or defect” seems to leave the psychiatrist too free to testify according to his judgment about the defendant’s criminal responsibility.26
This kind of testimony does not give the jury a satisfactory basis for determining criminal responsibility. A proper adjudication requires that the jury be fully informed about the defendant’s mental and emotional processes and, insofar as it affects these processes, his social situation.27 Of course, we cannot hope to obtain all the relevant information about a defendant. We cannot explore in full the effects of his genetic structure, his family relationships, his upbringing in slum or suburb. But within the limits imposed by the courtroom context and the level of scientific knowledge we should provide the jury with as much of this information as is reasonably available. We are not excused from doing what we can do simply because there are things we cannot do.
With the relevant information about defendant, and guided by the legal principles enunciated by the court, the jury must decide, in effect, whether or not the defendant is blameworthy. Undoubtedly, .the decision is often painfully difficult, and perhaps its very difficulty ac[454]*454counts for the readiness with which we have encouraged the expert to decide the question. But our society has chosen not to give this decision to psychiatrists or to any other professional elite but rather to twelve lay representatives of the community. The choice was not made on a naive assumption that all jurors would be fully capable of dealing with these difficult questions or with the underlying information. Nonetheless, this decision, along with many equally difficult ones in other areas, ranging from negligence to antitrust, was given to a jury.28 As long as this is our system, we should try to make it work.
The trial judge should limit the psychiatrists’ use of medical labels— schizophrenia, neurosis, etc.29 It would be undesirable, as well as difficult, to eliminate completely all medical labels, since they sometimes provide a convenient and meaningful method of communication. But the trial judge should ensure that their meaning is explained to the jury and, as much as possible, that they are explained in a way which relates their meaning to the defendant.30
[455]*455The problem with labels, such as, “product” and “mental disease or defect,” is even more difficult. Because these labels are employed in the legal test for responsibility, there is a danger that the psychiatric witness will view them as a legal-moral rather than a medical matter. There are two possible solutions. We could simply prohibit testimony in terms of “product” and “mental disease or
defect.” Or we could clearly instruct the expert to stick to medical judgments and leave legal-moral judgments to the jury.
A strong minority of this court has consistently advocated that psychiatrists be prohibited from testifying whether the alleged offense was the “product” of mental illness, since this is part of the ultimate issue to be decided by the jury.31 We now adopt [456]*456that view. The term “product” has no clinical significance for psychiatrists. Thus there is no justification for permitting psychiatrists to testify on the ultimate issue. Psychiatrists should explain how defendant’s disease or defect relates to his alleged offense, that is, how the development, adaptation and functioning of defendant’s behavioral processes may have influenced his conduct. But psychiatrists should not speak directly in terms of “product,” or even “result” or “cause.”
It can be argued that psychiatrists should also be prohibited from testifying whether the defendant suffered from a “mental disease or defect,” since this too is part of the ultimate issue. But unlike the term “product,” the term “mental disease or defect” may have some clinical significance to the psychiatrist. Moreover, prohibition of testimony about “mental disease or defect” would not be a panacea. Other words and other concepts may similarly be transformed into labels. For example, in McDonald we spoke about “abnormal” conditions of the mind, about impairment of mental and emotional processes, and about control mechanisms.32 The transcript of this trial illustrates how easily these concepts can become slogans, hiding facts and representing nothing more than the witness’s own conclusion about the defendant’s criminal responsibility.
At least for now, rather than prohibit testimony on “mental disease or defect,” we shall try to help the psychiatrists understand their role in court, and thus eliminate a fundamental cause of unsatisfactory expert testimony. A copy of the explanatory instruction to psychiatrists which we have set out in the Appendix should accompany all or[457]*457ders requiring mental examinations so that the psychiatrists will be advised of the kind of information they are expected to provide. To ensure that counsel and the jury are also so advised, the trial judge should give the explanatory instruction in open court to the first psychiatric witness immediately after he is qualified as an expert. It need not be repeated to later witnesses. Some of it will be repeated in the court’s instruction to the jury at the end of the trial, but we think the jury should hear it in full and before the testimony. Although an instruction at this juncture is not usual, this court has required one in somewhat analogous circumstances.33
Affirmed.
Appendix
Court’s Instruction to Expert Witness in Cases Involving the “Insanity Defense.”
Dr. _, this instruction is being given to you in advance of your testimony as an expert witness, in order to avoid confusion or misunderstanding. The instruction is not only for your guidance, but also for the guidance of counsel and the jury.
Because you have qualified as an expert witness your testimony is governed by special rules. Under ordinary rules, witnesses are allowed to testify about what they have seen and heard, but are not always allowed to express opinions and conclusions based on these observations. Due to your training and experience, you are allowed to draw conclusions and give opinions in the area of your special qualifications. However, you may not state conclusions or opinions as an expert unless you also tell the jury what investigations, observations, reasoning and medical theory led to your opinion.
As an expert witness, you may, if you wish and if you feel you can, give your opinion about whether the defendant suffered from a mental disease or defect. You may then explain how defendant’s disease or defect relates to his alleged offense, that is, how the development, adaptation and functioning of defendant’s behavioral processes may have influenced his conduct. This explanation should be so complete that the jury will have a basis for an informed judgment on whether the alleged crime was a “product” of his mental disease or defect. But it will not be necessary for you to express an opinion on whether the alleged crime was a “product” of a mental disease or defect and you will not be asked to do so.
It must be emphasized that you are to give your expert diagnosis of the defendant’s mental condition. This word of caution is especially important if you give an opinion as to whether or not the defendant suffered from a “mental disease or defect” because the clinical diagnostic meaning of this term may be different from its legal meaning. You should not be concerned with its legal meaning. Neither should you consider whether you think this defendant should be found guilty or responsible for the alleged crime. These are questions for the court and jury. Further, there are considerations which may be relevant in other proceedings or in other contexts which are not relevant here; for example, how the defendant’s condition might [458]*458change, or whether he needs treatment, or is treatable, or dangerous, or whether there are adequate hospital facilities, or whether commitment would be best for him, or best for society. What is desired in this case is the kind of opinion you would give to a family which brought one if its members to your clinic and asked for your diagnosis of his mental condition and a description of how his condition would be likely to influence his conduct. Insofar as counsel’s questions permit, you should testify in this manner.
When you are asked questions which fall within the scope of your special training and experience, you may answer them if you feel competent to do so; otherwise you should not answer them. If the answer depends upon knowledge and experience generally possessed by ordinary citizens, for example questions of morality as distinguished from medical knowledge, you should not answer. You should try to separate expert medical judgments from what we may call “lay judgments.” If you cannot make a separation and if you do answer the question nonetheless, you should state clearly that your answer is not based solely upon your special knowledge. It would be misleading for the jury to think that your testimony is based on your special knowledge concerning the nature and diagnosis of mental conditions if in fact it is not.
In order that the jury may understand exactly what you mean, you should try to explain things in simple language. Avoid technical terms whenever possible. Where medical terms are useful or unavoidable, make sure you explain these terms clearly. If possible, the explanation should not be merely general or abstract but should be related to this defendant, his behavior and his condition. Where words or phrases used by counsel are unclear, or may have more than one meaning, you should ask for clarification before answering. You should then explain your answer so that your understanding of the question is clear. You need not give “yes or no” answers. In this way any confusion may be cleared up before the questioning goes on.
Some final words of caution. Because we have an adversary system, counsel may deem it is his duty to attack your testimony. You should not construe this as an attack upon your integrity. More specifically, counsel may try to undermine your opinions as lacking certainty or adequate basis. We recognize that an opinion may be merely a balance of probabilities and that we cannot demand absolute certainty. Thus you may testify to opinions that are within the zone of reasonable medical certainty. The crucial point is that the jury should know how your opinion may be affected by limita-tations of time or facilities in the examination of this defendant or by limitations in present psychiatric knowledge. The underlying facts you have obtained may be so scanty or the state of professional knowledge so unsure that you cannot fairly venture any opinion. If so, you should not hesitate to say so. And, again, if you do give an opinion, you should explain what you did to obtain the underlying facts, what these facts are, how they led to the opinion, and what, if any, are the uncertainties in the opinion.