(dissenting, with whom Cowin, J., joins). I agree with the court that a Superior Court judge and the single justice erred in ordering pretrial disclosure to the Commonwealth’s expert witness, Dr. Martin Kelly, of the interview notes and psychological test results prepared by Dr. Daniel Brown, the licensed forensic psychologist retained by the defendant as an expert witness as to the defendant’s lack of criminal responsibility. I also agree with the court that, after defense counsel said in his opening statement that he would offer the expert testimony of Dr. Brown and after Dr. Kelly’s expert report was provided to the defendant, the judge properly ordered disclosure of Dr. Brown’s expert report to Dr. Kelly and the prosecution.
I dissent on three grounds. First, I do not agree that, in view of the testimony offered on direct examination at trial by Dr. Brown, it would have been error for the trial judge, before cross-examination, to have ordered disclosure to Dr. Kelly and the prosecution of the over 200 pages of interview notes and psychological testing materials on which Dr. Brown relied in proffering his opinion. Dr. Brown’s expert report described the documents he reviewed and the date and length of his interviews with the defendant, listed the psychiatric conditions from which he concluded the defendant suffered,1 and stated his ultimate opinion that “those conditions, in combination, caused [the defendant] to lack substantial capacity to appreciate the wrongfulness or criminality of her conduct, and resulted in her having a *332lack of substantial capacity to conform her conduct to the requirements of the law on July 28, 2004.” His report did not state a single fact on which he based his psychiatric diagnosis or his opinion, and did not provide a summary of the grounds for his opinion.2 Nor did his report identify any statement made by the defendant during their interviews or any test result that supported his psychiatric diagnosis or opinion. However, during his direct examination, Dr. Brown read verbatim statements of the defendant from his interview notes and testified in detail about the results of eleven different psychological tests given to the defendant.
Without access to the interview notes and the test results, the prosecution could not know whether the rule of completeness was satisfied when Dr. Brown read selected portions of the defendant’s statements made to him during their interviews, whether Dr. Brown had “cherry picked” the statements he had chosen to read from his notes or read them out of context, or whether the psychological test results were fairly and accurately characterized to the jury. The court concedes that, if “a defendant’s expert psychiatric witness is ‘cherry picking’ the defendant’s statements at trial, ... a trial judge has discretion to entertain remedial measures, which may include the required disclosure to the prosecution of any notes the defendant’s expert may have on the substance of the defendant’s statements to the expert” (emphasis in original). Ante at 323 n.31. Of course, the flaw in this reasoning is that a trial judge will not know that the witness is “cherry picking” unless the opposing attorney demonstrates the unfair selectivity, and the opposing attorney will not be able to demonstrate the unfair selectivity unless she has access to all the expert’s notes regarding the substance of the defendant’s statements to the expert, which the court’s decision today precludes.
In fact, the record at trial in this case shows that, when Dr. Brown testified on direct examination, he did “cherry pick” certain statements from what the defendant had told him in their *333interviews. Dr. Brown testified on direct examination that, when he first began interviewing the defendant, she had no memory at all of the events that occurred on the day she killed her husband. He said that he conducted a test for “memory malingering,” and that she did not respond on the test “like a person trying [to] fake loss of memory.” He later testified:
“During her dissociative state, she had substantial loss of awareness. She . . . she wouldn’t see anything. She . . . could hear no sounds. She could still feel bodily sensations during the report of a struggle with her husband, but there was no awareness of normal sensory perceptions. She couldn’t see the environment. She couldn’t hear anything for a substantial period of time. There was substantial time loss. And she wasn’t aware of actions; for example, she talked about having blood on her, but she wasn’t aware of how it got there.”
While this testimony reasonably would have left the jury with the impression that the defendant had virtually no memory of the day of the killing, Dr. Brown’s notes reflect that the defendant recalled a great deal about that day — that she woke up that morning wanting to kill herself, picked up a paring knife from the kitchen counter, and put the knife to her throat but ultimately pulled back from slitting her throat; that she grabbed a larger kitchen knife from the knife holder, went to the bedroom where her husband lay sleeping, and saw her husband jump at her when he saw that she was going to hurt herself; that a struggle ensued in which she felt pain as her husband tried to get something away from her and that he pushed, pulled, and kicked her; that she heard her husband make a sound after the struggle stopped, like someone vomiting; that when the struggle ended, she saw her husband lying motionless on the floor and “something red” on the floor and on her arms and hands; and that she then washed the blood from her arms and hands and covered his body with a sheet from the linen closet. Therefore, if in the court’s view there must be evidence of “cherry picking” to justify disclosure to the prosecution of the interview notes of the defendant’s expert witness, there is abundant evidence here.
As to the psychological test results, the court takes no position whether they were discoverable, inviting the court’s standing advisory committee on the criminal rules to consider the *334question. See ante at 323 n.31 & 325-326. As a result, the court cannot conclude that it would have been error for those test results to have been disclosed to Dr. Kelly and the prosecution after the defendant’s opening statement in this case. The importance of and justification for such disclosure is demonstrated by the trial record in this case, where Dr. Kelly in his rebuttal testimony disputed whether Dr. Brown had fairly and accurately interpreted the psychological test results that, according to Dr. Brown’s testimony, constituted the most significant evidence for his determination that on the day of the killing the defendant was unable to appreciate the wrongfulness of her conduct.
Second, where the only error concerns the timing of disclosure to the prosecution of the interview notes and psychological test results, not the substance of disclosure, I do not agree that this error of timing resulted in prejudicial error. The court, while effectively admitting to the possibility that disclosure of Dr. Brown’s interview notes and test results may have been permissible, appears to conclude that prejudicial error resulted from the premature disclosure of these materials to Dr. Kelly (but not the prosecutor) on January 27 and, subsequently, to the prosecution on February 16,3 rather than following Dr. Brown’s direct testimony on February 22. This premature disclosure could only have resulted in prejudice to the defendant if the prosecutor’s cross-examination of Dr. Brown or Dr. Kelly’s rebuttal testimony would have been materially different (and less persuasive to the jury) had they first received the interview notes and psychological test results following Dr. Brown’s direct testimony on February 22. There is no reason to believe that such prejudice occurred.
If the disclosure of Dr. Brown’s materials on February 22, after his direct examination, had denied the prosecutor or Dr. Kelly a fair opportunity to read and consider the interview notes and psychological test results before undertaking cross-examination of Dr. Brown or direct examination of Dr. Kelly, we would expect the judge to have granted the Commonwealth a continuance to give the prosecutor and Dr. Kelly that fair opportunity. The court’s reversal of the defendant’s conviction here rests on a conclusion that, if the judge had permitted disclosure of Dr. Brown’s interview notes and psychological *335test results only after Dr. Brown’s direct testimony, the defendant would have benefited because the prosecutor would have had too little time to employ the materials effectively on cross-examination of Dr. Brown, and Dr. Kelly would have had too little time to use them thoughtfully in formulating his opinions. To put it bluntly, in the court’s view, the prejudice that resulted from early disclosure is that the Commonwealth was able to make too effective use of information to which it was entitled. I know of no other conviction reversed on so meager a foundation.4
My third ground of disagreement with the court concerns the circumstances under which, following Mass. R. Crim. R 14, as appearing in 442 Mass. 1518 (2004), and as amended, 444 Mass. 1501 (2005), a judge may order disclosure of a defense expert’s interview notes and psychological test results to the prosecution. I conclude that a defense expert’s interview notes and psychological test results, like a defense expert’s report, are subject to reciprocal discovery after the Commonwealth’s expert report, interview notes, and psychological test results are provided to the defendant and after defense counsel in opening statement commits to present the opinion of the defendant’s expert, where that opinion rests in whole or in part on the defendant’s statements to the expert.5
To explain why I differ with the court, I need to examine the *336evolution of our law of discovery in the context of a criminal defendant’s claim of lack of criminal responsibility. For all practical purposes, that history began in 1977, when we considered the case of Blaisdell v. Commonwealth, 372 Mass. 753 (1977) (Blaisdell). In that case, after the defendant had filed a written statement declaring his intention to present a defense based on lack of criminal responsibility, the judge allowed the Commonwealth’s motion directing the defendant to submit to psychiatric examination by an expert selected by the Commonwealth, and ruled that, if the defendant refused to cooperate in the examination, he would be foreclosed from raising an insanity defense at trial. Id. at 754. In issuing this order, the judge relied on G. L. c. 123, § 15 {a), which authorizes a judge in a criminal case to order an examination of a defendant by a qualified physician or psychologist if the judge doubts whether the defendant is criminally responsible due to mental illness or mental defect.6 Blaisdell, supra at 754-755. The defendant petitioned this court for relief from the judge’s order under G. L. c. 211, § 3, and a single justice reserved and reported two questions to the full court: (1) may a defendant who discloses that he intends to interpose a defense of insanity at trial and who has sought no discovery from the Commonwealth be foreclosed from presenting expert psychiatric testimony at trial if he refuses to cooperate at a court-ordered psychiatric examination to determine criminal responsibility, and (2) if the defendant cooperates with the court-ordered psychiatric examination, to what extent may a report or the testimony of the examining psychiatrist be used at trial? Blaisdell, supra at 755 & n.l.
In answering the first question in the affirmative, we interpreted G. L. c. 123, § 15 (a), to avoid conflict with a defendant’s constitutional privilege against compelled self-incrimination when the defendant has given notice of his intention to introduce the testimony of a psychiatrist to support a defense of lack of criminal responsibility. Blaisdell, supra at 757-766. The court declared:
“If ... a defendant voluntarily submits to psychiatric *337interrogation as to his inner thoughts, the alleged crime and other relevant factors bearing on his mental responsibility and, on advice of counsel, voluntarily proffers such evidence to the jury, we feel that the offer of such expert testimony based in whole or in part on a defendant’s testimonial statements constitutes a waiver of the privilege for such purposes. . . . [A] defendant who seeks to put in issue his statements as the basis of psychiatric expert opinion in his behalf opens to the State the opportunity to rebut such testimonial evidence in essentially the same way as if he himself had testified.”
Id. at 766. Because the defendant’s proffer of an expert opinion at trial by a defense psychiatrist7 based, at least in part, on information provided by the defendant, constituted a waiver of the defendant’s constitutional privilege against self-incrimination, this privilege was not violated by an order compelling the defendant to submit to an examination by the prosecution’s psychiatrist.8 Id.
Our decision in Blaisdell, however, did not require the Commonwealth to wait until the defendant’s psychiatric expert had testified at trial before permitting its expert to interview the defendant. Such a rule, we concluded, would be unsatisfactory because it would either necessitate a continuance of the trial or leave too little time for a prosecution expert to examine the defendant and formulate an informed opinion as to criminal responsibility. Id. at 767. Instead, we held that, when a defendant declares his intent to offer expert testimony in support of his defense of lack of criminal responsibility and further declares that the testifying expert will rely in whole or in part on the defendant’s own statements regarding his mental state at or about the time of the commission of the alleged crime, the *338judge may order the defendant to submit to a pretrial psychiatric examination pursuant to G. L. c. 123, § 15, provided the judge also issues a protective order declaring, inter alia:
“The experts conducting the examination ordered by the court may not reveal to the prosecution or anyone acting in its behalf any evidence, statements, confessions or admissions obtained from the defendant except evidence derived from solely physical or physiological observation or tests, except as ordered by the court”; and
“Psychiatrists who conduct the examination ordered by the court shall file a written report of their findings with the court including a specific statement of what the basis of such findings may be, and such report shall not be available to either prosecution or defense unless, on inquiry by the court, the court determines that it does not contain any matter, information or evidence based on the defendant’s testimonial statements. ... If the report contains matter within the scope of the privilege, it shall be sealed and shall not be available to either party until such time during the course of the trial as the defendant raises the issue of insanity and makes clear to the court his intent either (a) to testify in his own behalf or (b) to place in evidence the testimony of psychiatric witnesses whose testimony will be based in whole or in part on the defendant’s extrajudicial or judicial statements.”
Id. at 768.
Under such a protective order, if before trial a defendant reconsiders his trial strategy and decides not to proceed with an insanity defense or not to call to testify any expert witness who has based his opinion on an interview of the defendant (thereby preserving his privilege against self-incrimination), the defendant’s and the prosecution’s interests are both protected: the testimonial fruits of the defendant’s compelled interview with the government’s expert will be unavailable for use against the defendant, directly or indirectly, and the information developed during the court-ordered examination will not taint the Commonwealth’s case. Id. at 762, and cases cited.
Because the issue presented to us in Blaisdell only concerned the application of G. L. c. 123, § 15 (a), we had no occasion *339there to address in what circumstances, if any, the Commonwealth could obtain discovery of an expert report or other material prepared by the defendant’s psychiatrist. We first addressed that issue in 1979, when we promulgated the rules of criminal procedure. Pretrial discovery was governed by Mass. R. Crim. P. 14, 378 Mass. 874 (1979). Under rule 14 (a) (1), which instituted mandatory, pretrial discovery for the defendant, on motion of the defendant a judge was required to order discovery of the defendant’s written or recorded statements, any written or recorded grand jury testimony, and any exculpatory facts within the custody or control of the Commonwealth. Rule 14 (a) (2) gave a judge discretion to order other discovery for the defendant, including “statements of persons, or reports of physical or mental examinations of any person or of scientific tests or experiments” within the prosecutor’s custody or control. Rule 14 (a) (3) provided for limited reciprocal discovery. If a judge had ordered discretionary discovery for the defendant under rule 14 (a) (2), on motion of the Commonwealth, the judge could require the defendant to provide reciprocal discovery to the prosecution of information discoverable under rule 14 (a) (2), including reports of mental examination and “statements of those persons whom the defendant intends to use as witnesses at trial.”9 Mass. R. Crim. P. 14 (a) (3). See Commonwealth v. Paszko, 391 Mass. 164, 187 (1984). Therefore, under rule 14 (a) (3), a judge could order a defendant to provide the prosecution with the defense psychiatrist’s expert report and statements, but only if the defendant intended to call the psychiatrist as a witness at trial and only after the prosecution had provided to the defendant the report and statements of the psychiatrist it intended to call in rebuttal.
Rule 14 (b) (2) addressed the Commonwealth’s examination *340of a defendant raising a defense of lack of criminal responsibility. Because rule 14 (b) (2) adopted the procedures established in Blaisdell to govern a compelled psychiatric examination of the defendant by the prosecution’s examiner, if the examiner’s report contained any information or evidence based on statements of the defendant as to his mental condition or criminal responsibility, a defendant could not be obligated to provide reciprocal discovery regarding his expert’s opinion until a judge had first unsealed the prosecution’s examiner’s report and made it available to the defendant. See Mass. R. Crim. R 14 (a) (3) and (b) (2). Rule 14 (b) (2) did not permit a judge to release the examiner’s report until the defendant raised the defense of lack of criminal responsibility at trial and the judge was satisfied that the defendant intended either to testify in his own behalf or to offer expert testimony based in whole or in part on the defendant’s statements as to his mental condition or criminal responsibility. If the prosecution’s examiner’s report did not contain any information or evidence that was based on statements of the defendant as to his mental condition or his criminal responsibility, the rule allowed a judge to unseal and make the report available to the defendant earlier. Mass. R. Crim P. 14 (b) (2) (B) (iii). This earlier disclosure, according to rule 14 (a) (3) and subject to the judge’s discretion, could in turn trigger an earlier reciprocal disclosure to the prosecution of the defendant’s expert report and statements.
*339“(A) If the judge grants discovery or inspection to a defendant pursuant to subdivision (a) (2) of this rule, the judge may upon motion by the Commonwealth condition his order by requiring the defendant to permit the Commonwealth to discover, inspect, and copy any material and relevant evidence discoverable under subdivision (a) (2) which the defendant intends to use at trial, including the names, addresses, and statements of those persons whom the defendant intends to use as witnesses at trial.”
*340The reciprocal discovery provisions of rule 14 (a) (3) did not distinguish between defense expert reports that contained or relied on statements of the defendant and those that did not; all were subject to reciprocal discovery in the court’s discretion. If the prosecution’s examiner’s report did not contain or rely on any statement of the defendant, a judge was not required to find that the defendant had waived his privilege against self-incrimination before ordering the defendant to turn over to the Commonwealth information developed by the defendant’s psychiatric expert. The privilege against self-incrimination does not apply to a defendant’s statements to the psychiatrist retained by his attorney because these statements were not compelled by the Commonwealth or the court; the defendant voluntarily chose to speak to his defense expert. See Commonwealth v. Seabrooks, *341433 Mass. 439, 451 (2001) (admission in evidence of defendant’s statements to psychologist did not violate privilege against self-incrimination where State did not compel defendant to speak to psychologist).10
Nevertheless, disclosure to the prosecution of the defense expert’s reports and statements must still wait until the defendant decides whether the expert will testify at trial based in whole or in part on the defendant’s statements to the expert, because, until that decision is made, the defendant’s statements to a defense expert retained by his attorney are protected by the attorney-client privilege. Reports and statements arising from such communications, while not within the compass of a defendant’s privilege against self-incrimination, are protected by the work product doctrine. See Commonwealth v. Bing Sial Liang, 434 Mass. 131, 138 (2001), quoting United States v. Nobles, 422 U.S. 225, 238 (1975) (“work product protection of rule 14 extends to an attorney’s legal staff, for ‘attorneys often must rely on the assistance of. . . agents in the compilation of materials in preparation for trial’ ”); Commonwealth v. Haggerty, 400 Mass. 437,441 (1987) (defense expert opinion subject to reciprocal discovery only when defendant intends to call expert as witness). Before a defendant decides that the defense expert will testify at trial, the role his examining psychiatrist holds is that of a consultant to the defense attorney on the issue of criminal responsibility, and the psychiatrist’s discussions with the defendant are therefore protected by the attorney-client privilege. Once the defendant decides to call the psychiatrist as a witness, however, the expert is no longer a defense consultant, but a trial witness. When this expert witness testifies at trial to the defendant’s statements or rests his opinion in whole or in part on such statements, the defendant waives any attorney-*342client privilege or work product doctrine protection that previously shielded from discovery his communications with the defense expert and the written reports and statements prepared by that expert witness. See United States v. Nobles, supra at 239-240 (communications to attorney’s agent protected under attorney-client privilege, but defendant waives privilege with respect to matters covered in agent’s testimony where defendant elects to call agent as witness).
In 2004, we adopted substantial revisions to rule 14. Among these revisions was an expansion of the category of mandatory discovery for the defense, which now included “[i]ntended expert opinion, other than evidence that pertains to the defendant’s criminal responsibility and is subject to subdivision (b)(2)” (emphasis added).11 Mass. Crim. P. 14 (a) (1) (A) (vi). Because the prosecution was required under the revised rule to provide mandatory discovery to the defendant at or before the pretrial conference, see Mass. R. Crim. P. 14 (a) (1) (A), we needed to exclude from mandatory discovery the prosecution’s expert opinion regarding criminal responsibility, which remained subject to rule 14 (b) (2) and therefore would be filed with the court and sealed until at or near the commencement of trial.
Another revision to rule 14 was to make reciprocal discovery mandatory on the prosecution’s delivery to the defendant of all information required under rule 14 (a) (1). Mass. R. Crim. P. 14 (a) (1) (B), as amended, 444 Mass. 1501 (2005)12; Reporters’ Notes to Rule 14 (a) (1) (B), Mass. Ann. Laws Court Rules, *343Rules of Criminal Procedure 1489-1490 (LexisNexis 2008-2009) (prosecution receives discovery only after it has produced discovery for defense). Prior to the 2004 revision, reciprocal discovery had been subject to the judge’s discretion. See Commonwealth v. Durham, 446 Mass. 212, 234, cert, denied, 549 U.S. 855 (2006) (Durham). Because rule 14 (a) (1) (A) (vi) excludes from the Commonwealth’s automatic discovery obligations expert opinion evidence “that pertains to the defendant’s criminal responsibility and is subject to subdivision (b) (2),” and rule 14 (a) (1) (B) now requires the defendant to disclose to the prosecution evidence “discoverable under subdivision (a) (1) (A) (vi),” the court infers that in modifying rule 14, we intended that rule 14 (a) “not apply to discovery related to the defense of criminal responsibility, because all procedures and provisions applicable to such discovery are set out in rule 14 (b) (2).” Ante at 319. This is not a fair inference for two reasons.
*342“Following the Commonwealth’s delivery of all discovery required pursuant to subdivision (a) (1) (A) or court order, and on or before a date agreed to between the parties, or in the absence of such agreement a date ordered by the court, the defendant shall disclose to the prosecution and permit the Commonwealth to discover, inspect, and copy any material and relevant evidence discoverable under subdivision (a) (1) (A) (vi), (vii) and (ix) which the defendant intends to offer at trial, including the names, addresses, dates of birth, and statements of those persons whom the defendant intends to call as witnesses at trial.”
*343First, the exclusion in our revised rule 14 (a) (1) (A) (vi) simply means that expert opinion evidence that pertains to the defendant’s criminal responsibility is beyond the scope of mandatory discovery and therefore falls, as it did under the earlier version of the rule, within the rubric of discretionary discovery. Subdivision (b) (2) therefore continues to control the scope of the judge’s discretion regarding disclosure of the prosecution’s expert witness report; but it is silent as to discovery of the written statements and reports of the defendant’s expert. Under the original rule 14 promulgated in 1979, all expert discovery fell within the rubric of discretionary discovery, and once the prosecution had furnished discovery of its expert opinion evidence to the defendant, a trial judge could order the defendant to provide reciprocal discovery regarding the expert witnesses the defendant intended to call at trial, including those who would testify to the defendant’s lack of criminal responsibility. There is no reason to believe that by imposing a mandatory reciprocal discovery obligation on defendants in the 2004 revisions, we intended to eliminate the judge’s authority to order reciprocal discovery of expert psychiatric opinion. If we had intended such a result, one would think our intent would have been reflected in the language of the revised rule or, at a minimum, in the Reporters’ Notes.13 The silence of both sources on this issue *344speaks loudly to our intent to leave the judge’s discretionary authority unchanged with regard to reciprocal discovery in this context.
Second, we said in 1984, and again in 2006, that rule 14 favors “liberal discovery.” Durham, supra at 221, 222, quoting Commonwealth v. Paszko, 391 Mass. 164, 188 (1984). In Commonwealth v. Paszko, supra at 187-188, applying the policy of “liberal discovery” we said was embodied in the rule, we affirmed a judge’s reciprocal discovery order requiring a defendant to disclose to the prosecution the prior statements of witnesses the defendant intended to call at trial that were included within the defendant’s investigator’s report, even though under Federal law such statements would have been deemed protected attorney work product. We stated that the “policy of our rules is that the availability of statements of nonparty witnesses gathered by an adversary serves a truth-enhancing function . . . that outweighs any resulting inconvenience or potential disincentive to lawyers who obtain and preserve such statements in written form.” Id. at 188. In reaching our decision, we noted that similar witness statements had been provided by the prosecution to the defense and used by defense counsel for impeachment purposes. With this in view, we declared that a “defendant is not constitutionally entitled to a discovery system that operates only to his benefit.” Id.
In Durham, supra at 213-214, which was decided after adoption of the revised rule 14 but applied the pre-2004 version, id. at 213 n.l, we affirmed a judge’s reciprocal discovery order requiring a defendant to disclose prior statements of witnesses that the Commonwealth, not the defendant, intended to call at trial. Explaining that the “trial process seeks to ascertain the truth,” id. at 226, and that “criminal trials are matters of justice and not sporting events,” id. at 229, we discussed the importance of reciprocal discovery in ensuring that “both sides are given a fair opportunity to investigate the veracity of [witness] statements and are not faced with confronting them for the first time at trial.” Id. at 225. The court was sharply split in the Durham *345case as to whether reciprocal discovery applied to a defense investigator’s report of prior statements made by witnesses called by the prosecution. All seven Justices agreed, however, that rule 14 permitted a judge to order reciprocal discovery of prior statements made by persons whom the defendant intended to call as witnesses at trial. See Durham, supra at 233 (Cordy, J., dissenting, with whom Marshall, C.J., and Ireland, J., joined). Justice Cordy declared that “ [Requiring discovery of such statements is in line with the modem trend to guard against surprise defenses, thereby ensuring that both prosecutor and defendant are ready to argue the principal issues in the case at trial.”14 Id. In view of our strong belief in liberal discovery, which the Durham case restated in 2006, it would be astonishing if in revising rule 14 two years earlier, we had intended to forbid reciprocal discovery of the prior statements of a witness the defendant intended to call at trial regarding the defendant’s lack of criminal responsibility.
From this history, and from my interpretation of rale 14, I conclude that a judge has discretion to order a defendant to disclose expert opinion evidence pertaining to the defendant’s criminal responsibility after the judge discloses to the defendant the expert opinion evidence prepared by the prosecution’s expert examiner under mle 14 (b) (2), which will occur only after the defendant waives the attorney-client privilege regarding his discussions with the defense expert psychiatrist, either by having the expert witness testify at trial to the defendant’s statements; or by offering in evidence the expert’s opinion that rests in whole or in part on such statements; or by committing in counsel’s opening statement to offer such evidence. The expert opinion evidence that may be ordered disclosed includes all “ statements] ” of the expert witness, which, as defined in rale 14 (d), includes not only expert reports but also all relevant writings prepared by the witness “other than drafts or notes that have been incorporated into a subsequent draft or final report.” Id.
*346As discussed earlier, a psychiatrist testifying as an expert witness for the defense who has not disclosed his interview notes and psychological test results could on the witness stand “cherry pick” certain statements of the defendant that supported his opinion and ignore those that did not, and could misread or mischaracterize test results, all without risk of being held to account for such conduct on cross-examination. Without access to the expert’s written work product, a prosecutor would be unaware of these shadings and omissions and, as a result, would be unable to reveal them to the jury. “[W]e have repeatedly emphasized the importance that cross-examination plays in the ‘fact finder’s assessment of the truth. ’ ” Durham, supra at 230 (Marshall, C.J., dissenting), quoting Commonwealth v. Vardinski, 438 Mass. 444, 450 (2003).
The Commonwealth would have been unfairly disadvantaged if it had been denied discovery of the written statements, test results, and expert report on which Dr. Brown relied in reaching his opinion. Without this discovery, the prosecutor, in cross-examining Dr. Brown, would not have been able to point to statements made by the defendant to Dr. Brown, which he failed to mention on direct examination, that failed to support his opinion that the defendant at the time of the killing was unaware of her surroundings, unaware of her actions, and not criminally responsible for her conduct. It was within the judge’s discretion to assure that the jury would have an opportunity to consider all of the information that Dr. Brown reviewed in formulating his opinion, not just a truncated portion favorable to the defendant. See United States v. Nobles, 422 U.S. 225, 241 (1975). “The adversary system of trial is hardly an end in itself; it is not yet a poker game in which players enjoy an absolute right always to conceal their cards until played” (footnote omitted). Williams v. Florida, 399 U.S. 78, 82 (1970).
I conclude, therefore, that neither the trial judge nor the single justice erred in ordering the defendant to disclose to the prosecution Dr. Brown’s expert report, the detailed notes of his interview of the defendant (as those were not incorporated into his final report), and the results of the psychological tests he considered. The only error was in the timing of the disclosure of the interview notes and test results, which should not have been ordered until after the defendant’s opening statement. In *347that opening statement, the defendant committed to present the expert testimony of Dr. Brown, which was based “in whole or in part upon statements of the defendant as to . . . [her] mental condition at the time of, or criminal responsibility for, the alleged crime.” Mass. R. Crim. R 14 (b) (2) (B) (iii). With that commitment by defense counsel, the defendant waived both her privilege against self-incrimination and her attorney-client privilege as to statements she had made to her attorney’s expert consultant, Dr. Brown. She likewise surrendered any protection she may have enjoyed under the work product doctrine with respect to Dr. Brown’s writings regarding his evaluation of the defendant. The defendant’s waiver of her privilege against self-incrimination in the opening statement justified the disclosure of Dr. Kelly’s expert report to the prosecution and to the defense, and this disclosure in turn justified the order of reciprocal discovery requiring the defendant to disclose Dr. Brown’s report, testing data, and interview notes.
This error in timing was not constitutional in nature; it involved a breach of the attorney-client privilege that protected the defendant’s communications with Dr. Brown until the defendant waived that privilege by committing at trial to calling Dr. Brown to the witness stand. The error did not involve a breach of the defendant’s privilege against self-incrimination under the Fifth Amendment to the United States Constitution or art. 12 of the Massachusetts Declaration of Rights. Consequently, we should apply the prejudicial error standard, which requires us to ask whether we are “sure that the error did not influence the jury, or had but very slight effect.” Commonwealth v. Flebotte, 417 Mass. 348, 353 (1994), quoting Commonwealth v. Peruzzi, 15 Mass. App. Ct. 437, 445 (1983). Here, we can say with fair assurance that the judgment of conviction was not substantially swayed by the error, and that the error was nonprejudicial. Id. The defendant has given us no reason to believe, and I find none after reviewing Dr. Kelly’s testimony, that Dr. Kelly’s testimony at trial on February 23, 2006, would have been any different or any less persuasive to the jury had Dr. Kelly first seen Dr. Brown’s notes and test results after opening statements on February 16, 2006, rather than on January 27, 2006.
Because I conclude that the only error regarding reciprocal *348discovery was one of timing and that this error was harmless when considered in view of the entire record, I respectfully dissent.
Dr. Brown’s report concluded that on the date of the killing, the defendant suffered from (1) major depressive disorder; (2) posttraumatic stress disorder; (3) panic disorder; (4) axis II personality disorder (mixed with primary dependent personality disorder); and (5) major dissociative disorder (dissociative amnesia and dissociative disorder not otherwise specified). The report stated that each diagnosis was based on the criteria set forth in the Diagnostic and Statistical Manual of Mental Disorders (4th ed. 2004).
If Dr. Brown had been an expert witness in a civil case, and answered expert interrogatories without stating a single fact on which he based his psychiatric diagnosis or his opinion, or providing a summary of the grounds for his opinion, the opposing party could justly have moved for and obtained an order compelling further answers to these interrogatories to comply with the requirements in Mass. R. Civ. R 26 (b) (4) (A), 365 Mass. 772 (1974).
The judge permitted Dr. Kelly to share this information with the prosecutor after the defendant’s opening statement on February 16, 2006.
I know of no authority to support a conclusion that premature disclosure to the Commonwealth of reciprocal discovery to which the prosecution is entitled results in prejudicial error. We have, however, frequently held that late disclosure to a defendant of exculpatory or other evidence to which the defendant is entitled did not result in prejudicial error. See Commonwealth v. Baldwin, 385 Mass. 165, 175-176 (1982) (exculpatory evidence); Commonwealth v. Gilbert, 377 Mass. 887, 894-895 & n.7 (1979) (incriminating prior statements of prosecution witness). In reviewing this sort of error, “it is the consequences of the delay that matter, not the likely impact of the nondisclosed evidence, and we ask whether the prosecution’s disclosure was sufficiently timely to allow the defendant ‘to make effective use of the evidence in preparing and presenting his case.’ ” Commonwealth v. Baldwin, supra at 175, quoting Commonwealth v. Wilson, 381 Mass. 90, 114 (1980). In such circumstances, a delay results in prejudice only if, after considering the entire record, we conclude that “given a timely disclosure, the defense would have been able to prepare and present its case in such a manner as to create a reasonable doubt that would not otherwise have existed.” Commonwealth v. Baldwin, supra, quoting Commonwealth v. Wilson, supra.
I agree with the court’s suggestion that these issues should be addressed by the court’s standing advisory committee on the criminal rules.
The relevant provisions of G. L. c. 123, § 15 (a), have not changed since our decision in Blaisdell v. Commonwealth, 372 Mass. 753 (1977) (Blaisdell). Compare St. 1971, c. 760, § 12, with St. 1986, c. 599, § 38.
I refer to a psychiatrist, but an expert opinion of a psychologist or clinical social worker would be treated identically.
In Commonwealth v. Callahan, 386 Mass. 784, 789 (1982) (Callahan), we clarified that the “defendant, by voluntarily proffering such evidence to the jury, has waived his privilege against self-incrimination to a limited extent,” recognizing that the limitations on the use of the defendant’s compelled interview required by G. L. c. 233, § 23B, would apply. Under § 23B, no statement made by a defendant during a compelled psychiatric examination may be admissible in evidence against him on any issue other than the defendant’s mental condition, and may not be admissible even for that limited purpose “if such statement constitutes a confession of guilt of the crime charged.”
The relevant reciprocal discovery language of Mass. R. Crim. R 14 (a) (3), 378 Mass. 874 (1979), provided:
We have not carved out an exception to the defendant’s obligation to provide reciprocal discovery of “statements of those persons whom the defendant intends to call as witnesses” under Mass. R. Grim. R 14 (a) (1) (B), as amended, 444 Mass. 1501 (2005), to exclude prior written statements made by the witness preserving what the defendant previously said to that witness. See Commonwealth v. Durham, 446 Mass. 212, 213-214, 219-221, cert, denied, 549 U.S. 855 (2006) (Durham) (order of reciprocal discovery requiring defendant to furnish Commonwealth with prior statements of witnesses to be called at trial, whether by Commonwealth or defendant, is lawful and “violates no Federal or State constitutional right of the defendant”).
Rule 14 (b) (2) of the Massachusetts Rules of Criminal Procedure, as appearing in 442 Mass. 1518 (2004), which incorporated the elements of the protective order in Blaisdell, remains, apart from minor revisions, essentially unchanged from the 1979 version.
The provision in Mass. R. Crim. P. 14 (a) (1) (B), as amended, 444 Mass. 1501 (2005), regarding reciprocal discovery reads in its entirety:
In fact, the Reporters’ Notes to the 2004 revision of Rule 14, Mass. Ann. *344Laws Court Rules, Rules of Criminal Procedure 1483 (LexisNexis 2008-2009), begin by stating: “This rule is based on the concept of reciprocity and has as its aim full pretrial disclosure of items normally within the range of discovery.”
In fact, defenses based on mental illness or disease were among the particular “surprise defenses” to which Justice Cordy specifically referred, noting with approval that the off-setting provision for pretrial discovery under rule 14 (b) fell within the trend toward reciprocal discovery that served to reduce such surprises. See Durham, supra at 240 (Cordy, J., dissenting, with whom Marshall, C.J., and Ireland, J., joined).