Explaining Away Jesus’ Resurrection: The Recent Revival of Hallucination Theories


Gary R. Habermas

Article ID:



Jul 27, 2023


Jun 9, 2009

This article first appeared in the Volume 23 / Number 4 / 2001 issue of the Christian Research Journal. For further information or to subscribe to the Christian Research Journal go to: http://www.equip.org/



A survey of over 1000 recent publications on Jesus’ resurrection reveals some intriguing trends. For example, after almost a century of virtual dormancy, some critical scholars have proposed a number of naturalistic alternative hypotheses to explain away Jesus’ resurrection. Similar to the situation at the end of the Nineteenth Century, the most popular response by critics today is that the disciples experienced some sort of subjective perceptions of Jesus, although He had not been raised from the dead. Hallucination (more properly termed subjective vision) hypotheses come in different varieties. Sometimes it is suggested that the resurrection appearances of Jesus were similar to the recent claims that the Virgin Mary has appeared. Other times, it is said that these subjective visions were normal responses to grief by Jesus’ disciples, or perhaps even due to a psychological disorder. All of these recent strategies have something else in common, too: each one fails by a large margin to explain the historicity of Jesus’ resurrection appearances. These inadequacies are due to an entire host of problems. This is the result even when these views are judged by critically accepted standards. In fact, perhaps the main reason why most scholars still hesitate to propose alternative scenarios to explain away the resurrection is that numerous historical critiques stand in the way of these naturalistic approaches. Even critical scholars usually agree.


Naturalistic explanations of Jesus’ resurrection have existed as long as this event has been proclaimed. Several of these alternative approaches even appear in the Gospels themselves. It seems that both past and present skeptics, knowing that Christ’s resurrection lies at the heart of Christianity, have singled it out for special attack. In this article I will first provide historical perspective to this issue and make brief comments regarding the heyday of naturalistic theories in nineteenth-century theology. About 100 years ago, the hallucination hypothesis was the most popular critical position until it passed out of scholarly favor. Based on my recent survey of more than 1,000 publications on the subject of Jesus’ resurrection published between 1975 and the present, I will proceed to document the increased popularity of this hypothesis, focusing chiefly on the views of scholars during the past decade or two. Lastly, I will present a multifaceted critique of these positions, using only data that can be ascertained by critical means, which the vast majority of scholars will accept.1


Publications from the end of the eighteenth through the nineteenth century provide the most examples of naturalistic theories regarding Jesus’ resurrection. In his classic volume documenting studies of the historical Jesus during this period, Albert Schweitzer chronicled many of these approaches. For example, an early attempt by Hermann Reimarus charged that Jesus’ disciples stole His dead body.2 Friedrich Schleiermacher favored the swoon theory, arguing that Jesus never died on the cross.3 David Strauss popularized the hallucination theory,4 and others such as Ernest Renan followed him.5 Otto Pfleiderer and others thought that legends explained much of the data.6

A fascinating subplot is that many liberal scholars refuted competing hypotheses. Schleiermacher and Heinrich Paulus attacked various vision theories.7 Strauss is usually thought to have crushed the swoon thesis with his insightful analysis8 so that few scholars supported it after his critique.9 Even though he preferred the legend thesis, Pfleiderer even admitted that it could not fully explain the data for Jesus’ resurrection.10

During most of the twentieth century, there was comparatively little interest in naturalistic theories against Jesus’ resurrection. Those who rejected the historicity of this event seldom made reference to alternative formulations. After mentioning a lengthy list of critical theories, Raymond Brown indicated in 1967 that the “criticism of today does not follow the paths taken by the criticism of the past. No longer respectable are the crude theories…popular in the past century….Serious scholars pay little attention to these fictional reconstructions.”11

This lull on the part of critical scholars occurred for more than one reason. Interest in many issues regarding the historical Jesus sagged during this period. Near the top of the list of reasons was the failure of naturalistic hypotheses to explain the known data. In other words, the chief reason for rejecting these alternative theories is that the facts refute each one. James D. G. Dunn concluded: “Alternative interpretations of the data fail to provide a more satisfactory explanation.”12 Philosopher Stephen Davis agrees that critics “are unable to come up with a coherent and plausible story that accounts for the evidence at hand. All of the alternative hypotheses with which I am familiar are historically weak; some are so weak that they collapse of their own weight once spelled out….the alternative theories that have been proposed are not only weaker but far weaker at explaining the available historical evidence.”13

Despite these developments, at present there appears to be a limited trend toward rejuvenating some of the older attempts to explain the resurrection on naturalistic grounds. Of these, the most popular recent choice is a thesis that involves the earliest Christians having hallucinatory or other subjective experiences.


In my survey of over 1,000 critical publications on the resurrection, more scholars apparently support various naturalistic hypotheses than has been the case in many decades. This phenomenon is not due to any change in the historical landscape. Rather, it is like the old saying — what goes around comes around — as if some scholars simply think it is time for a change.

Of those who now prefer hallucination explanations, however, only a few scholars have pursued this approach in detail, while several other scholars simply mention the possibility of, or preference for, the hallucination thesis.14 We will look at a few of these attempts.

Gerd Lüdemann has recently outlined a case reminiscent of nineteenth-century attempts. He holds that this explanation can be applied to all of the chief participants in the earliest church: the disciples, Paul, the 500, and James, the brother of Jesus.15 Lüdemann asserts that Paul’s use of the term ophthe in 1 Corinthians 15:3ff clearly means that he was speaking of actual sight, of “his own active sensual perception…,” as well as that of the other apostles. So Paul “must have expected the Corinthians to understand the term historically.”16 Lüdemann concludes that hallucinatory visions are required, along with “auditory features” that produced a “stimulus,” “enthusiasm,” “religious intoxication,” and “ecstasy” for Peter. This spread to the other disciples by “an incomparable chain reaction.” Paul, the other apostles, 500 persons, and James all similarly experienced these subjective visions. The appearances were collective, amounting to a “mass ecstasy.”17

Although his approach is quite different at points, Jack Kent also thinks hallucinations explain the claims of the disciples, Paul, and James.18 Kent combines two naturalistic theories to explain the resurrection appearances of Jesus. Jesus’ male and female followers experienced “normal, grief-related hallucinations.” Paul, on the other hand, experienced inward conflict and turbulence because he participated in the death of Stephen and because of his persecution of Christians. As a result, he underwent a “conversion disorder,” a recognized psychiatric malady that accounts for his conversion on the road to Damascus, which included his stumbling and blindness in particular.19 Unlike Lüdemann, however, Kent wishes to avoid collective hallucinations.20

Closer to Kent, Michael Goulder applies a related explanation to the experiences of Peter, Paul, and some of the others.21 Goulder thinks that Peter and Paul experienced what he calls “conversion visions” — hallucinations of various sorts produced during times of great stress, guilt, and self-doubt. The result for these apostles, one of whom

had denied his Lord and another who had persecuted Christians, was a new orientation to life — a transformation leading to “subsequent heroism and martyrdom.”22

One other approach I have dubbed “the illumination theory” should perhaps be mentioned briefly. Several recent scholars prefer a strategy that, while seemingly close to the hallucination thesis, is not quite the same. In general, the idea is that Peter was the first to have some sort of subjective experience or conviction that Jesus was alive. This was later communicated in some sense to Jesus’ other followers, who concluded that Jesus had risen. Critics contend that we cannot now speak about the historical nature of this incident. It is the faith of the early believers that is really of chief importance here, not the nature of the experiences.23 It is often remarked that these experiences were not hallucinations,24 but many of our criticisms below will still apply to this thesis.


While recent hallucination theories reveal some differences among them, there are more similarities. We will begin our critiques by evaluating the possibility of group hallucinations. Next, we will look at the conversion disorder thesis proposed by Kent and Goulder. Then we will examine additional problems with these subjective explanations of Jesus’ resurrection.

Collective Hallucinations

One of the central issues in this entire discussion concerns whether a group of people can witness the same hallucination. Most psychologists dispute that possibility. A rare attempt suggesting that collective hallucinations are possible, without any application to Jesus’ resurrection, is made by Leonard Zusne and Warren Jones. They point to phenomena such as claimed sightings of the Virgin Mary and other accompanying reports from groups of people. In cases such as these, “expectation” and “emotional excitement” are “a prerequisite for collective hallucinations.” In such groups, we see the “emotional contagion that so often takes place in crowds moved by strong emotions.…”25

The idea of collective hallucinations, however, is highly problematic on several grounds:

1. The chief examples of “collective hallucinations” provided by Zusne and Jones were religious group experiences such as with Marian apparitions. These examples simply beg the question whether such experiences could possibly be objective, or even supernatural, at least in some sense. In other words, why must a naturalistic, subjective explanation be assumed?26 This approach seems to rule out the apparitions in an a priori manner, before the data are considered.

2. Furthermore, the collective hallucination thesis is unfalsifiable. It could be applied to purely natural, group sightings, simply calling them group hallucinations, too. Concerning this thesis, crucial epistemic criteria seem to be missing. It can be used to explain (away) almost any unusual occurrence. How do we determine normal occurrences from group hallucinations?

3. Even if it could be established that groups of people experienced hallucinations, it does not mean that these experiences were therefore collective. If, as most psychologists assert, hallucinations are private, individual events, then how could groups share exactly the same subjective visual perception? Rather, it is much more likely that the phenomena in question are either illusions — perceptual misinterpretations of actual realities27 — or individual hallucinations.

Moreover, the most serious problems result from comparing this thesis to the New Testament accounts of Jesus’ resurrection appearances. Here, the explanatory power of this hypothesis is severely challenged, since much of the data not only differs from, but actually contradicts, the necessary conditions for “collective hallucinations.”

4. For instance (more examples will follow below), Zusne and Jones argue that “expectation” and “emotional excitement” are “prerequisites” before such group experiences can occur. In fact, expectation “plays the coordinating role”;28 but these necessary elements contradict the emotional state of the early witnesses of Jesus’ resurrection appearances. The early believers were confronted with the utter reality of the recent and unexpected death of their best friend, whom they had hoped would rescue Israel. As those events unfolded in a whirlwind of incidents that included Jesus’ physical beatings, crucifixion, and seeming abandonment, the normal response would have been fear, disillusionment, and depression. To suppose that these believers exhibited “expectation” and “emotional excitement” in the face of these stark circumstances would require responses on their part that would scarcely be exhibited at a funeral! All indications are that Jesus’ disciples exhibited the very opposite emotions from what Zusne and Jones assert as being necessary for such hallucinations.

By comparison, the disciples’ experience was totally unlike those cases where pilgrims expressly traveled long distances, exuberantly gathering with the explicit desire to see something special, as in the Marian cases. There would seem to be extremely meager grounds for comparison here with Jesus’ disciples.29

Many other crucial problems plague the thesis of group hallucinations, and we will pursue several more below. For now, we repeat that Zusne and Jones never even attempt to apply their approach to Jesus’ resurrection. Rather, they incredibly close their examination with the admission that group hallucinations have a “dubious status” because it is not possible to ascertain whether these individuals were actually hallucinating!30

Conversion Disorder

Kent has suggested that Paul experienced a “conversion disorder,” a psychological condition characterized by such physical symptoms as blindness or paralysis in the absence of specific neurological or medical causes. This was brought about by his inner turbulence, conflict, doubt, and guilt. Goulder agrees about Paul, but adds that Peter and others, including perhaps James, were also suffering from the same problem.

Again, when we align their hypotheses with the known facts, multiple problems with their interpretation emerge:

1. Initially, only Paul is known to have manifested any such symptoms. Goulder’s inclusion of the others is not factually grounded.

2. The psychological profile provided for conversion disorder also strongly opposes an application to Paul, James, or Peter. It most frequently occurs in women (up to five times more often), adolescents and young adults, less-educated persons, people with low I.Q.s or low socioeconomic status, and combat personnel.31 Not a single characteristic applies to Paul and it would be difficult to prove them for the other two apostles.

3. A major problem is that no evidence exists to posit the preconditions for such a disorder from what we know about Paul, and about James in particular. Critics agree that James was an unbeliever during Jesus’ earthly ministry (John 7:5; cf. Mark 3:21). We have no indication that James experienced the slightest inner conflict, doubt, or guilt concerning his previous rejection of Jesus’ teachings. Paul’s skepticism is even better known, since he persecuted early Christians (1 Cor. 15:9; Gal. 1:13, 23). We do not know of any guilt on Paul’s part either, for he considered his actions to have been both zealous and faultless (Phil. 3:4-6). In short, there is no indication of any prior desire for conversion by either of these men. To suppose otherwise is groundless. Paul and James are thus exceptionally poor candidates for this disorder.

4 and 5. Here, we have two separate critiques, due to very different sets of circumstances. While the same cannot be said of Peter, there is no indication that either James or Paul longed to see Jesus. Their unbelief is a poor basis for producing hallucinations! James the skeptic and Paul the persecutor are exceptionally tough obstacles for the hallucination thesis. To say otherwise is mere conjecture apart from historical data. Not only are these two individuals poor candidates for hallucination, but we need both visual and auditory hallucinations, which stretches the case even further. These two phenomena are relatively uncommon occurrences.32 These two apostles, therefore, fail to qualify for the disorder in the first place, and even apart from this malady, they were additionally not predisposed to experience hallucinations.

6. Neither does this hypothesis normally account for what would otherwise be considered delusions of grandeur — in this case, the apostles’ belief that God had imparted to them a global message that others must accept. It is unlikely that other delusions were involved here, occurring at precisely the same time. So the case is further weakened in that the thesis fails to explain all of the known data.

Charging that these apostles were victims of conversion disorder simply does not fit the facts. It is clearly an over-reliance on a hypothesis apart from the data, a theory not anchored to reality. It would be highly improbable for all of the necessary factors to converge simultaneously. Like the charge of mass hallucinations, it spawns more difficulties than it tries to solve.

Additional Problems

Many other issues remain regarding the hallucination hypothesis:

1. Even individual hallucinations are questionable for believers who felt despair at the unexpected death of Jesus just hours before. Their hopes and dreams had suddenly been dashed. Extreme grief, not exuberance, would have been their normal response.

2. The wide variety of times and places that Jesus appeared, along with the differing mindsets of the witnesses, is another formidable obstacle. The accounts of men and women, hard-headed and soft-hearted alike, all believing that they saw Jesus, both indoors and outdoors, provide an insurmountable barrier for hallucinations. The odds that each person would be in precisely the proper and same frame of mind to experience a hallucination, even individually, decrease exponentially.33

3. Generally, hallucinations do not transform lives. Studies indicate that even those who do hallucinate often disavow the experiences when others present have not seen the same thing.34 Critics acknowledge that Jesus’ disciples were transformed even to the point of being willing to die for their faith. No early text reports that any of them ever recanted. It is highly unlikely that this quality of conviction came about through false sensory perceptions without anyone rejecting it later.

4. If the appearances were hallucinations, then opponents should have located Jesus’ body safely and securely in His grave just outside the city of Jerusalem. That body would undoubtedly be a rather large disclaimer to the disciples’ efforts to preach that Jesus was raised! Because the hallucination hypotheses do not even address the historical arguments for the empty tomb, another naturalistic thesis is required in order to do so.

Still more issues weaken the hallucination hypothesis. While they are perhaps not as weighty, they nevertheless count:

5. Why did the hallucinations stop after 40 days? Why didn’t they continue to spread to other believers, just as the other hallucinations had?

6. The resurrection was the disciples’ central teaching, and we usually take extra care with what is closest to our hearts. This is what drove Paul to check out the nature of the gospel data with other key disciples on at least two occasions to make sure he was preaching the truth (Gal. 1:18–19; 2:1–10). He found that they were also speaking of Jesus’ appearances to them (1 Cor. 15:11).

7. What about the natural human tendency to touch? Would not one of them ever discover, even in a single instance, that his or her best friend, seemingly standing perhaps just a few feet away, was not really there?

8. The resurrection of a contemporary individual contradicted general Jewish theology, which held to a corporate resurrection at the end of time. So Jesus’ resurrection did not fit normal Jewish expectations, and most of the witnesses to Jesus’ bodily resurrection were Jewish.

9. Finally, hallucinations of the extended sort required by this naturalistic theory are rare phenomena, chiefly occurring in circumstances that militate against Jesus’ disciples being the recipients.35


To sum up, after a century-long hiatus, a limited trend toward the reformulation of naturalistic approaches to Jesus’ resurrection has recently emerged. The hallucination and related subjective hypotheses are again the most popular among these approaches, as they were at the close of the nineteenth century. We have seen that these strategies have failed to explain the known, critically ascertained data on several fronts. Giving a total of 19 reasons, we have concluded that they fall far short in their attempt to provide an alternative to the New Testament proclamation. Clinical psychologist Gary Collins summarizes a few of the issues: “Hallucinations are individual occurrences. By their very nature only one person can see a given hallucination at a time. They certainly are not something which can be seen by a group of people….Since an hallucination exists only in this subjective, personal sense, it is obvious that others cannot witness it.”36

In fact, the problems with this thesis are so serious that these recent critics “would have to go against much of the current psychiatric and psychological data about the nature of hallucinations.”37 These approaches are therefore at odds with current scientific knowledge on this subject. To apply the hallucination and similar subjective theses to Jesus’ resurrection appearances is erroneous across several disciplines and at many points. These subjective theories fail just as thoroughly as did those of 100 years ago to undermine the proclamation on which Christian faith has stood firm for 2,000 years: Christ is risen. He is risen, indeed!

Gary R. Habermas (Ph.D., Michigan State University) is Distinguished Professor of Apologetics and Philosophy at Liberty University, Lynchburg, VA. Of his 21 books, nine are on the subject of Jesus’ resurrection.



  1. This is what I have termed “the minimal facts method,” which argues primarily from data that are multiply attested on strongly evidential grounds. Almost all scholars who research this subject accept these data. For an outline of this method, see Gary R. Habermas, “Evidential Apologetics,” Five Views on Apologetics, ed. Steven Cowan (Grand Rapids: Zondervan, 2000), 99–120, 186–90.
  2. Albert Schweitzer, The Quest of the Historical Jesus: A Critical Study of Its Progress from Reimarus to Wrede, trans. W. Montgomery (New York: Macmillan, 1906, 1968), 21–22; other examples are found on pp. 21–22, 43, 47, 53–55, 60, 83, 162–67, 170, 187, 210–14.
  3. Schweitzer, 64; Friedrich Schleiermacher, The Christian Faith, trans. H. R. Mackintosh and J. S. Stewart, 2 vols. (New York: Harper and Row, 1963), 417–21.
  4. David Strauss, A New Life of Jesus, 2d ed., 2 vols. (Edinburgh: Williams and Norgate, 1879), vol. 1, 412–40.
  5. Ernest Renan, Vie de Jesus (Paris: Calmann-Levy, 1861), 355–56.
  6. Otto Pfleiderer, Early Christian Conception of Christ: Its Significance and Value in the History of Religion (London: Williams and Norgate, 1905), chap. 4.
  7. Schleiermacher, 420; Schweitzer, 53–55.
  8. Strauss, 408–12.
  9. Schweitzer lists no convinced proponents of the swoon theory after 1838, three years after the initial publication of Strauss’s critique.
  10. Pfleiderer, 157–58.
  11. Raymond Brown, “The Resurrection and Biblical Criticism,” Commonweal, 24 November 1967, 233.
  12. James Dunn, The Evidence for Jesus (Louisville: Westminster, 1985), 76.
  13. Stephen Davis, “Is Belief in the Resurrection Rational? A Response to Michael Martin,” Philo 2 (Spring–Summer 1999): 57–58.
  14. Some of these are Dan Cohn-Sherbok, “The Resurrection of Jesus: A Jewish View,” Resurrection Reconsidered, ed. Gavin D’Costa (Oxford: Oneworld, 1996), 197; John Barclay, “The Resurrection in Contemporary New Testament Scholarship,” in D’Costa, 25–26; Michael Grant, Saint Paul: The Man (Glasgow: William Collins Sons, 1976), 108; M. Lloyd Davies and T. A. Lloyd Davies, “Resurrection or Resuscitation?” Journal of the Royal College of Physicians of London 25 (April 1991): 168; Antony Flew in Gary R.
  15. Gerd Lüdemann’s best known works are: The Resurrection of Jesus: History, Experience, Theology, trans. John Bowden (Minneapolis: Fortress, 1994); a more popular rendition was written in collaboration with Alf Ozen, What Really Happened to Jesus: A Historical Approach to the Resurrection, trans. John Bowden (Louisville: Westminster John Knox, 1995).
  16. Lüdemann, The Resurrection of Jesus, 50, 37; cf. What Really Happened to Jesus, 103.
  17. Lüdemann, The Resurrection of Jesus, 106–7, 174–75.
  18. Jack Kent, The Psychological Origins of the Resurrection Myth (London: Open Gate, 1999).
  19. Ibid., 6–11, 49–61, 85–90.
  20. Ibid., 89–90.
  21. Michael Goulder, “The Baseless Fabric of a Vision,” in D’Costa, 48–61; a briefer version was published as part of a debate with James Dunn in Resurrection, ed. G. N. Stanton and S. Barton (London: SPCK, 1994), 58–68.
  22. Goulder, 48–52. Incidentally, Goulder argues that the disciples, especially regarding Jesus’ appearances to groups, experienced “collective delusions.” These are significantly different from subjective hallucinations in that they pertain to the misapprehension of actual, physical objects (52–55).
  23. Similar views are held by: Willi Marxsen, Jesus and Easter: Did God Raise the Historical Jesus from the Dead? (Nashville: Abingdon, 1990), 65–74; Willi Marxsen, The Resurrection of Jesus of Nazareth, trans. Margaret Kohl (Philadelphia: Fortress, 1968), especially chaps. 3–4; Don Cupitt, Christ and the Hiddenness of God (Philadelphia: Westminster, 1971), 143, 165–67; Thomas Sheehan, The First Coming: How the Kingdom of God Became Christianity (New York: Random House, 1986), 95–118; John Shelby Spong, Resurrection: Myth or Reality? (San Francisco: HarperSan Francisco, 1994), 255–60; John Shelby Spong, The Easter Moment (San Francisco: HarperSan Francisco, 1987), especially 39–68.
  24. Spong, The Easter Moment, 196; Sheehan, 262-63, n. 38; cf. Marxsen, Jesus and Easter, 71–74.
  25. Leonard Zusne and Warren Jones, Anomalistic Psychology: A Study of Extraordinary Phenomena of Behavior and Experience (Hillsdale, NJ: Lawrence Erlbaum, 1982), 135–36.
  26. For a number of critical observations and responses to such phenomena, see Elliot Miller and Kenneth R. Samples, The Cult of the Virgin: Catholic Mariology and the Apparitions of Mary (Grand Rapids: Baker, 1992), esp. chaps. 11–14 and appendix A.
  27. Here, Zusne and Jones repeatedly refer to collective hallucinations, even though they conclude, conversely, that these groups may be seeing actual phenomena. So the “final answer to these questions has not been obtained yet” (135–36)!
  28. Ibid., 135.
  29. The rejoinder could be made that perhaps a few individuals hallucinated individually, thereby inducing excitement in the others, preparing them for hallucinations. From our critique below, a multifaceted response could be fashioned. I would suggest especially critiques 4–5 in the next section regarding the cases of Paul and James, which would be highly problematic for this view both because of the initial skepticism and the later conversions of these apostles, plus critiques 2–8 in the “Additional Problems” section below.
  30. Ibid., 136; cf. 134–35. For the more common assessment against group hallucinations, see Phillip Wiebe, Visions of Jesus: Direct Encounters from the New Testament to Today (New York: Oxford, 1997), 210; J. P. Brady, “The Veridicality of Hypnotic, Visual Hallucinations,” Origins and Mechanisms of Hallucinations, ed. Wolfram Keup (New York: Plenum, 1970), 181; Weston La Barre, “Anthropological Perspectives on Hallucinations and Hallucinogens,” Hallucinations: Behavior, Experience and Theory, ed. R. K. Siegel and L. J. West (New York: John Wiley and Sons, 1975), 9–10.
  31. Harold Kaplan, Benjamin Sadock, and Jack Grebb, Synopsis of Psychiatry, 7th ed. (Baltimore: Williams and Wilkins, 1994), 621.
  32. Ibid., 621–22. I am also indebted to clinical psychologist Gary Sibcy, Ph.D., for these last two responses.
  33. S. J. Segal, “Imagery and Reality: Can They Be Distinguished?” in Keup, 103–13. Zusne and Jones also note that even if people hallucinated in groups, not everyone would have these same experiences (135).
  34. Segal, 103. This observation is also corroborated in an unpublished study of hallucinations by Shea Lambert, “Hallucinations and the Post Death Appearances of Jesus,” 20 September 2000, 2–5, 8–9.
  35. For many details, see Wiebe, 199–200, 207–11; Kaplan, Sadock, and Grebb, 621. To repeat an earlier point, many of the objections throughout this essay also apply to what I have termed “the illumination theory.”
  36. Gary Collins, Ph.D., personal communication, 21 February 1977.
  37. Ibid.
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