1. Introduction
The incorporation of spirituality themes and foci within health psychology research is an emerging field (
,
Levin, 1996How religion influences morbidity and health: Reflections on natural history, salutogenesis, and host resistance.
). Although there is already a substantive literature examining various dimensions of spirituality with respect to a wide range of mental and physical disorders (
), there has been relatively little attention among researchers on the incorporation of spirituality in the treatment of the addictions (
) or in HIV risk-behavior studies. This lack of attention represents a considerable gap in our knowledge, given the prominence of such spirituality-oriented lay programs as Alcoholics Anonymous (AA) and Narcotics Anonymous (NA), whose 12-step programs have at their foundation the concept of addiction as a spiritual, as well as a medical and psychological, disorder (
). Members of AA view the 12 steps as providing guidance for a way of life, with spiritual processes such as a relationship with God or a higher power and prayer at its core (
Miller & Kurtz, 1999Models of alcoholism used in treatment: Contrasting AA and other perspectives with which it is often confused.
). Although the specific aspects of religiosity and spirituality that may influence recovery from addiction are at present unclear, the extent to which AA and NA members speak of a higher power as an important force for change (
Green et al., 1998- Green L.L
- Fullilove M.T
- Fullilove R.E
Stories of spiritual awakening. The nature of spirituality in recovery.
) suggests that spirituality is an important dimension to consider when studying recovery from addiction.
Research conducted to date supports the contention that spirituality is a relevant factor to include in addiction treatments (
Avants et al., 2001- Avants S.K
- Warburton L.A
- Margolin A
Spiritual and religious support in recovery from addiction among HIV-positive injection drug users.
,
Brizer, 1993Religiosity and drug abuse among psychiatric inpatients.
,
,
Kendler et al., 1997- Kendler K.S
- Gardner C.O
- Prescott C.A
Religion, psychopathology, and substance use and abuse: A multimeasure, genetic-epidemiologic study.
,
Mathew et al., 1996- Mathew R.J
- Georgi J
- Wilson W.H
- Mathew V.G
A retrospective study of the concept of spirituality as understood by recovering individuals.
,
,
Pardini et al., 2000- Pardini D.A
- Plante T.G
- Sherman A
- Stump J.E
Religious faith and spirituality in substance abuse recovery: Determining the mental health benefits.
).
Pardini et al., 2000- Pardini D.A
- Plante T.G
- Sherman A
- Stump J.E
Religious faith and spirituality in substance abuse recovery: Determining the mental health benefits.
found in a study of 237 recovering substance abusers that higher levels of religious faith and spirituality predicted a more optimistic life orientation, greater perceived social support, higher resilience to stress, and lower levels of anxiety. In addition, in a study of over 2000 female-female twins,
Kendler et al., 1997- Kendler K.S
- Gardner C.O
- Prescott C.A
Religion, psychopathology, and substance use and abuse: A multimeasure, genetic-epidemiologic study.
reported that current drinking and smoking as well as lifetime risk for alcoholism and nicotine dependence were inversely associated with personal devotion (such as frequency of praying and seeking spiritual comfort), fundamentalist Christian beliefs, and religious affiliation conservatism. Other smaller scale studies have come to similar conclusions (
Brizer, 1993Religiosity and drug abuse among psychiatric inpatients.
,
Mathew et al., 1996- Mathew R.J
- Georgi J
- Wilson W.H
- Mathew V.G
A retrospective study of the concept of spirituality as understood by recovering individuals.
). Religion and spirituality, as potential resources for recovery, may also be underutilized by clinicians who treat addicted individuals (
Goldfarb et al., 1997- Goldfarb L.M
- Galanter M
- McDowell D
- Lifshutz H
- Dermatis H
Medical student and patient attitudes toward religion and spirituality in the recovery process.
,
Miller, 1998Researching the spiritual dimensions of alcohol and other drug problems.
).
With respect to HIV risk-behavior research,
Des Jarlais et al., 1997- Des Jarlais D.C
- Vanichseni S
- Marmor M
- Buavirat A
- Titus S
- Raktham S
- Friedmann P
- Kitayaporn D
- Wolfe H
- Friedman S
- Mastro T.D
“Why I am not infected with HIV”: Implications for long-term HIV risk reduction and HIV vaccine trials.
found that over one third of HIV-negative injection drug users indicated that “prayer” or “God's help” was responsible for helping them avoid engaging in behaviors that could lead to HIV infection. Our own work (
Avants et al., 2001- Avants S.K
- Warburton L.A
- Margolin A
Spiritual and religious support in recovery from addiction among HIV-positive injection drug users.
) with inner-city HIV-positive injection drug users has shown that strength of perceived religious and spiritual support is an independent predictor of abstinence from illicit substances during methadone maintenance treatment, controlling for the influence of pre-treatment variables (addiction and psychiatric severity, CD4 count, social support, and optimism), and during-treatment variables (methadone dose and attendance at counseling sessions). We have also found a significant association between HIV risk behavior and strength of spiritual and religious faith and characteristics of drug users' assumptive worlds. Specifically, strong spiritual and religious faith, the perception that the world and the people in it are basically good, and the perception of a meaningful world (i.e., the belief that outcomes are just, are not randomly distributed, and can be controlled by personal behavior) emerged as independent predictors of high risk sexual behavior in a sample of methadone-maintained drug users (
Avants et al., in pressAvants, S. K., Marcotte, D., Arnold, R. M., & Margolin, A. (in press). Spiritual beliefs, world assumptions, and HIV risk behavior among heroin and cocaine users. Psychology of Addictive Behaviors.
).
Spirituality may be an especially salient dimension of recovery for HIV-positive drug users (
Biggar et al., 1999- Biggar H
- Forehand R
- Devine D
- Brody G
- Armistead L
- Morse E
- Simon P
Women who are HIV infected: The role of religious activity in psychosocial adjustment.
,
Demi et al., 1997- Demi A
- Moneyham L
- Sowell R
- Cohen L
Coping strategies used by HIV infected women.
,
Florence et al., 1994- Florence M.E
- Luetzen K
- Alexius B
Adaptation of heterosexually infected HIV-positive women: A Swedish pilot study.
,
Jenkins, 1995Religion and HIV: Implications for research and intervention.
,
Kaplan et al., 1997- Kaplan M.S
- Marks G
- Mertens S.B
- Terry D.J
Distress and coping among women with HIV infection: Preliminary findings from a multiethnic sample.
,
Tangenberg, 2001Surviving two diseases: Addiction, recovery, and spirituality among mothers living with HIV disease.
). These patients are faced with the stress of a chronic, and potentially fatal, disease as well as the daily challenges of becoming and remaining abstinent (
Carson et al., 1990- Carson V
- Soeken K.L
- Shanty J
- Terry L
Hope and spiritual well-being: Essentials for living with AIDS.
,
Jenkins, 1995Religion and HIV: Implications for research and intervention.
,
Tsevat et al., 1999- Tsevat J
- Sherman S.N
- McElwee J.A
- Mandell K.L
- Simbartl L.A
- Sonnenberg F.A
- Flowler F.J
The will to live among HIV-infected patients.
,
Woods & Ironson, 1999Religion and spirituality in the face of illness: How cancer, cardiac, and HIV patients describe their spirituality/religiosity.
). It has been suggested that religious faith may provide a buffer against the depressive effects of stressful life events (
Kendler et al., 1997- Kendler K.S
- Gardner C.O
- Prescott C.A
Religion, psychopathology, and substance use and abuse: A multimeasure, genetic-epidemiologic study.
), and may also play a protective role in physical and mental health (
Benson & Dusek, 1999Self-reported health and illness and the use of conventional and unconventional medicine and mind/body healing by Christian Scientists and Others.
,
Galanter, 1997Spiritual recovery movements and contemporary medical care.
,
).
Despite these encouraging findings, there are currently few research-based interventions that incorporate spirituality into addiction treatment. One reason for this may be the inherent difficulty of defining “spirituality.” An associated concern is that even if spirituality is operationally defined for purposes of developing an intervention, it may not be possible to address the diversity of beliefs and practices of the patient population. Indeed, current interest in spirituality within the mental health community has resulted in a plethora of articles, containing a number of different definitions (
Zinnbauer et al., 1999- Zinnbauer B.J
- Pargament K.I
- Scott A.B
The emerging meanings of religiousness and spirituality: Problems and prospects.
). It is clear that spirituality is a complex, wide-ranging, multidimensional concept (
), and there is well-recognized difficulty in creating a definition that encompasses all, or even many, of the apparently relevant dimensions of this concept, that avoids possible contamination with psychological or other existing constructs, and that is applicable across manifold populations and disorders (
,
,
,
).
Given both the complexity and diffuseness of the concept of spirituality, prior to embarking on the development and evaluation of a treatment intervention designed to incorporate patients' spiritual and religious faith in the treatment of addictive and HIV risk behaviors among HIV-positive and HIV-negative injection drug users, we conducted a study in order to gain a better understanding of the concept of spirituality from the perspective of patients. The study had three goals: (a) to explore how spirituality is defined by inner-city HIV-positive drug users; (b) to explore perceived relationships among spirituality and abstinence, harm reduction, and health promotion, and (c) to assess perceived helpfulness of a spirituality-based intervention for various aspects of recovery by sex, race, and HIV-serostatus.
To address the first two goals, focus groups were conducted with HIV-positive injection drug users. Focus groups are a method of qualitative research that assesses participants' attitudes and perceptions via researcher-initiated discussions concerning target topics that may be recorded for subsequent thematic study. The focus group methodology has been used to examine a variety of topics in the addictions (
,
Green et al., 1998- Green L.L
- Fullilove M.T
- Fullilove R.E
Stories of spiritual awakening. The nature of spirituality in recovery.
,
Nadeau et al., 1997- Nadeau L
- Truchon M
- Biron C
High-risk sexual behaviors in a context of substance abuse: A focus group approach.
,
Rhodes et al., 1999- Rhodes F
- Deren S
- Wood M.M
- Shedlin M.G
- Carlson R.G
- Lambert E.Y
- Kochems L.M
- Stark M.J
- Falck R.S
- Wright-DeAgüero L
- Weir B
- Cottler L
- Rourke K.M
- Trotter II, R.T
Understanding HIV risks of chronic drug-using men who have sex with men.
,
Shoultz et al., 2000- Shoultz J
- Tanner B
- Harrigan R
Culturally appropriate guidelines for alcohol and drug abuse prevention.
,
VanderWaal et al., 2001- VanderWaal C.J
- Washington F.L
- Drumm R.D
- Terry Y.M
- McBride D.C
- Finley-Gordon R.D
African-American injection drug users: Tensions and barriers in HIV/AIDS prevention.
) and was among several qualitative approaches included in a technical review on “Qualitative Methods in Drug Abuse and HIV Research,” sponsored by the National Institute on Drug Abuse (
Carlson et al., 1995Carlson, R. G., Siegal, H. A., & Falck, R. S. (1995). Qualitative research methods in drug and AIDS prevention research: An overview. In E. Y. Lambert, R. S. Ashery, & R. H. Needle (Eds.), Qualitative methods in drug abuse and HIV research. NIH Publication No. 95–4025 (Vol. 157, pp. 6–26). Rockville, MD: National Institute on Drug Abuse.
,
Shedlin & Schreiber, 1995Shedlin, M. G., & Schreiber, J. M. (1995). Using focus groups in drug abuse and HIV/AIDS research. In E.Y. Lambert & R.S. Ashery & R.H. Needle (Eds.), Qualitative Methods in Drug Abuse and HIV Research. NIH Publication No. 95–4025 (Vol. NIDA Research Monograph 157, pp. 136–155). Rockville, MD: National Institute on Drug Abuse.
). Focus groups are particularly useful for exploring participants' attitudes towards issues and concepts in order to appropriately incorporate them into systematic interventions (
). Our third goal was addressed by administering a brief questionnaire to a sample of HIV-positive and HIV-negative drug users.
3. Results
3.1 Focus groups
Participants in the focus groups seemed willing and eager to talk about their understanding of spirituality, and its role in their recovery. We were not sure how the topic would be received, as spirituality/religion could be a highly personal issue, or even a divisive issue for the groups, if interpretations of spirituality or religious backgrounds clashed. However, these concerns were fortunately unfounded: participants were mutually respectful of each other's views at all times. Furthermore, they often told highly personal testimonials concerning their religious/spiritual experiences and shared ways in which spirituality/religiousness has influenced their recovery, living with HIV, and engaging in risky behaviors.
Subsequent analysis of the focus group transcripts revealed two themes concerning how focus group participants usually conceived of, or expressed, spirituality in their daily lives: as protector/helper to self, and as altruistic/helpful to others. These conceptualizations were not mutually exclusive, and which one was prominent depended to some extent on the issue being discussed. The following section provides quotes from participants to illustrate the expression of these themes in a number of relevant subjects.
3.2 Definitions of spirituality
When introducing the topic for the focus group, participants were asked what first comes to mind when thinking of the word “spirituality.” Not surprisingly, many initial responses included organized religion, attending worship services, and God or a higher power. Examples of God or a higher power responses were: “Well, I'm a very religious person. It means how a certain person feels about their own spirituality, which means their relationship with God.” “Spirituality to me is believing in a person that you really care about the most. I use my daughter as my higher power.”
After these initial responses, the comments about spirituality shifted and tended to reveal a more internalized conceptualization, usually suggesting a view of spirituality as a protector or helper to self. Many referred to a subconscious or inner voice that “talked” to them while chastising or encouraging: “Even though I have made wrong choices, I knew what the right choices were and I went against my higher power inside of me telling me, ‘It's wrong. It could hurt you,’ or ‘You shouldn't do it.’”
Others viewed their spirituality as an inner source of strength or the sense of having found oneself, which also served as a helper to self: “I think it is just a struggle you as a person go through. Realizing the qualities you have inside of you, and the strength you have inside of you.” “Spirituality for me is when you are trying to find yourself.” For a few participants in one group, to be spiritual included helping others, the alternate theme that emerged about spirituality.
3.3 Spirituality and recovery from addiction
Praying and belief in a higher power were most commonly cited as coping strategies in recovery from addiction. As previously mentioned, 19 of the 21 participants prayed or meditated at least once or twice a week, with 8 of those praying on a daily-basis. Spirituality was conceived as a protector/helper to self in these comments, as group members asked for forgiveness or strength: “What I am saying is that I don't got the strength he [another participant] got. If you bring dope in here I can't say no….I want to get high. Therefore, I ask God, God Help me. Give me the strength so that I can say no.”
Many participants claimed that it was due to their belief in God that they had achieved abstinence in the past or were currently clean. This quote is typical of focus group members who used spirituality as protector/helper to self: “I incorporate the Lord in my life. Do what His will be, as best I could. Sometimes I succeed. Sometimes I fail. But I never give up. That is what works for me. It worked for me in the past. When I indulged myself into the Lord, I was clean. Because of that, spirituality, I was clean.” Another participant had this to say about maintaining her abstinence: “If God did not help me, if God wasn't there in my life, I don't think I'd be clean. I really don't….God gives me the strength to be clean.”
3.4 Spirituality and living with HIV
Many focus group members shared stories about near-death experiences, either because of drug overdoses, having full-blown AIDS, or suicide attempts, as well as about the deaths of friends and loved ones to AIDS. For others, living with HIV has resulted in a preoccupation with death. What is interesting about these experiences, and what ties them together, is that participants seem to have become more spiritual because of them. Having “looked death in the face” and survived has given many focus group members a new lease on life. On learning he was HIV-positive, this patient initially became depressed and suicidal, but then made a choice to live to glorify God: “Everything was wrong with me. And something told me inside myself, you have a choice. You can either continue down the path of destruction or you can ask God for forgiveness of what I have done in the past and what I have done today and continue on with my life.”
Testing HIV-positive provided the impetus to enter addiction treatment for a few. The following patient began to value his life and friendships more after learning he was HIV-positive: “For me AIDS, has taught me to value my life. To worry about my health….But when I became HIV, after I went through what I went, I said, I got to grow up. I wanted to change. I wanted to stop using drugs and doing what I was doing. It's like I was killing myself faster….And then when I accepted it, I started to value things. I started to value friendship.”
Others felt that the fact that they had come so close to death, or that they themselves were still healthy despite being HIV-positive, must mean that there was some reason they were supposed to be alive, a reason that did not include using drugs. “Why am I still this healthy? What is the reason here? I think that played a part in the reason for me trying to straighten out my life. You know? Quit being a jerk. What the hell are you doing? They've given you a freebie here. You're supposed to be dead.” Another patient stated: “I OD'ed [overdosed] twice. I mean literally died, and He brought me back….He brought me back for a reason. And then I'm living with HIV. There's got to be something out there today that He wants me to do.”
3.5 Spirituality and reducing HIV transmission
Few focus group participants spoke about spirituality explicitly in connection with whether they did or did not engage in risky sexual or drug-using practices that could result in HIV transmission. In addition, none of the group members admitted to having recently engaged in any sexual or needle-sharing behaviors that would put others at risk. The explanations they usually provided were altruistic.
Those who were married or had steady partners claimed that they used condoms when engaging in sexual intercourse. Love for their partners and a desire not to transmit HIV were cited as the primary reasons for engaging in safer sexual practices, both of which can be conceived to be altruistic. Focus group participants not involved in steady relationships were also altruistic; they usually stated that they engaged in safe sex, or at a minimum told their partners they were HIV-positive before engaging in sexual activity. As one patient stated, “Me, myself, personally, I have to let the person know [that I am HIV-positive], and then whether we use a condom or not, that's just an adult decision.”
With regard to needle sharing and the use of potentially contaminated needles, most participants claimed that easy access to clean needles in their community (e.g., the ability to purchase needles at a pharmacy and to obtain needles from needle exchange vans) has made needles a “non-issue” in terms of spreading HIV. Altruistic reasons cited for not letting others use their needles, at least unclean needles, included concern about the possibility of transmitting HIV to others, and that it was simply ‘the right thing to do.’ One participant expressed it this way: “I think about doing harm to people and what not, because I am a strong believer in that, the way I put it, what goes around comes around. You reap what you sow. I figure if I put someone else at risk or harm someone else, it's coming back my way one day.”
There were a few who explicitly cited their spiritual faith as the impetus for not sharing needles and other paraphernalia. “When I was ignorant, let's say, when I didn't know about this HIV needle thing, I shared needles like everybody else. I didn't have a higher power or spirituality to guide me to not do it. But, now it's like another life. It's like I am living in another century. I don't do the things I did before, because of my spirituality.”
Perhaps for the reasons they mention, mostly altruistic, focus group participants did not engage in risky sexual or drug-using behaviors. However, it should be noted that participants also met regularly in the context of their methadone maintenance treatment. Given that they would continue to interact with each other and with other methadone maintained patients, it is unlikely that they would be forthcoming with examples that indicated they had put others at risk.
3.6 Spirituality and adherence to medical recommendations
Many focus group participants were prescribed complex medical regimens for the treatment of HIV, whereas others indicated that their HIV health care provider did not feel HIV medications were yet necessary. Most of those taking medications did not attribute medication adherence to their spiritual faith. A few, however, did express thanks to God for the medications that allowed them to maintain their health; their comments contributed to the theme of spirituality as protector/helper to self. “I was on death's door, supposedly, and I thank God every day that the scientists were able to come up with the combination of medications that they did.” In addition, as noted previously, many focus group members are grateful that they are still alive, despite being infected with HIV and having watched friends die with AIDS. This sense of gratitude seemed to have inspired them to work hard to remain abstinent from illicit drugs, which, in turn, serves to maintain their health.
3.7 Patient interest in integrating spirituality into addiction treatment
Overall, focus group members reported interest in having a spiritual/religious component to their addiction treatment. This was evident throughout the course of the discussion, as well as from the PHS questions, discussed in the next section with the full sample. When asked if they felt a need for an intervention that would specifically integrate spirituality into their addiction treatment, most patients were supportive. “Oh, absolutely. I think I need it more than anything.” “Like once a week is good for me.”
3.8 Questionnaire: Perceived helpfulness of integrating spirituality into addiction treatment
Of the 47 methadone-maintained patients who completed the PHS questionnaire (Inter-item reliability alpha = .91), the majority reported that an intervention that integrated their spiritual and religious faith into addiction treatment would be helpful in their recovery. Median scores for the first four questions were 3.0 (‘a lot’), and for perceived effect on increasing hopefulness the score was 4 (‘extremely’). There were no main effects for sex, race, or HIV serostatus. However, there was a significant multivariate Sex by Race interaction; F(5, 38) = 2.56, p = .04. Subsequent univariate ANOVAs were significant for 3 of the 5 items (p < .05; df = 2,41; F = 4.33, 5.06, 5.26, respectively). Examination of simple effects tests revealed that African American females had higher mean scores than did African American males on perceived helpfulness of integrating spirituality into addiction treatment: females = 3.50 (±0.55); males = 1.71 (±1.50); t(11) = 2.75, p = .019; for HIV harm reduction: females = 3.00 (±1.55); males = 1.29 (±1.25); t(11) = 2.21, p = .049; and for increasing hopefulness: females = 3.67 (±0.52); males = 1.86 (±1.68); t(11) = 2.53, p = .028. There were no significant sex differences for white or Hispanic patients. Focus group participants did not differ from non-focus group participants on any item of perceived helpfulness of spirituality.
4. Discussion
We conducted an exploratory study aimed at assessing a number of issues germane to offering a spirituality-based treatment to methadone-maintained drug users enrolled in an inner-city MMP. During focus groups with HIV-positive drug users, participants were quite willing to discuss their own interpretations of spirituality and to share their spiritual/religious experiences. Despite the variability in how spirituality was conceptualized by participants, two primary themes emerged during the course of the focus groups: (a) spirituality as a source of personal strength/protector of self; and (b) spirituality as altruism/protector of others. Spirituality as protector of self was most evident when focus group members discussed their recovery from addiction, having to face their own mortality due to HIV, and available medical treatments, whereas spirituality as protector of others was most evident when participants talked about HIV harm reduction behavior (e.g., not sharing drug paraphernalia and not engaging in unsafe sexual practices).
The inner-city drug-users participating in the current study expressed an interest in being provided with an intervention that addresses spirituality. However, it was clear from the focus group discussions that any intervention that attempted to address the spiritual needs of drug users would need to be flexible enough to allow for several interpretations of spirituality, including a conceptualization of spirituality that does not include belief in a “higher power.” This is not to suggest that spirituality should be conceived as either theistic or non-theistic. Rather, individuals should be able to define it for themselves. As
Miller, 1998Researching the spiritual dimensions of alcohol and other drug problems.
: p. 980) states, spirituality is understood to be operative at the level of the individual, and its definition “must be one that does not rely upon particular religious contexts, that is accessible and observable regardless of one's personal beliefs, and that can thereby be used to characterize all people”.
Findings from the questionnaire administration among the larger sample indicated that participants thought that addressing spirituality in addiction treatment would be helpful in their recovery, for reducing craving, for reducing HIV risk behavior, for following medical recommendations, and particularly for increasing hopefulness. The vast majority expressed an interest in receiving a spirituality-focused intervention. There were no significant differences in perceived helpfulness of spirituality in recovery by HIV-serostatus. However, there was a Sex by Race interaction, with African American women perceiving spirituality as more helpful than did African American men, a finding that is generally consistent with the literature (
Kaplan et al., 1997- Kaplan M.S
- Marks G
- Mertens S.B
- Terry D.J
Distress and coping among women with HIV infection: Preliminary findings from a multiethnic sample.
). This latter finding suggests that researchers should be sensitive to possible gender, sex and cultural differences in how spirituality is perceived.
This study has several limitations that should be taken into consideration in the interpretation of findings. The focus groups were small and the participants were not randomly selected, and, therefore, the data may not be generalizable to larger populations. Furthermore, the participants knew one another and met regularly, suggesting that they might have been influenced more than usual to make socially appropriate responses. The data from the questionnaire are similarly based on a small sample, and should be interpreted conservatively. Lastly, it is possible that participants' past or current attendance at AA or NA meetings may have influenced them to respond in an “AA-appropriate” fashion.
Our finding that the incorporation of themes involving spiritual and religious faith into addiction treatment was welcomed by the drug users in our sample will come as no surprise to many substance abuse counselors, and certainly not to advocates of AA and NA self-help groups. Neither is the study of spirituality new to the field of psychology. On the subject of the spiritual self,
wrote over a century ago, “And the spiritual self is so supremely precious that, rather than lose it, a man ought to be willing to give up friends, good fame, property, and life itself” (p.315). James, as with many contemporary clinical psychologists and theorists (e.g.,
Miller, 1998Researching the spiritual dimensions of alcohol and other drug problems.
), also viewed spirituality as a dimension of human experience that warranted scientific investigation. We hope that findings such as ours, although preliminary, will encourage clinicians and researchers to develop spirituality-focused interventions that can be subjected to empirical evaluation.
Article info
Publication history
Accepted:
June 24,
2002
Received in revised form:
June 12,
2002
Received:
February 13,
2002
Copyright
© 2002 Elsevier Science Inc. Published by Elsevier Inc. All rights reserved.