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RESEARCH ARTICLE |
Departments of 1 Family, Consumer and Human Development, 2 Psychology, 3 Mathematics and Statistics
4 Center for Epidemiologic Studies, Utah State University, Logan.
5 Institute of Clinical Neurosciences, Göteborg University, Sweden.
6 Department of Mental Hygiene, The Johns Hopkins University, Baltimore, Maryland.
7 VA Puget Sound Health Care System and Department of Psychiatry and Behavioral Sciences, University of Washington, Seattle.
8 Department of Psychiatry and Behavioral Sciences and 9 The Joseph and Kathleen Bryan Alzheimer's Disease Research Center, Duke University, Durham, North Carolina.
Address correspondence to Maria C. Norton, PhD, Department of Family, Consumer and Human Development, Cache County Study on Memory Health and Aging, Utah State University, 4440 Old Main Hill, Logan, UT 84322-4440. E-mail: maria.norton{at}usu.edu
| Abstract |
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Key Words: Church Attendance Depression Latter Day Saints
LATE-LIFE depression has been estimated as the second major cause of disability among older adults (Judd, Akiskal, & Zeller, 2000
), affecting 6.5 million of Americans 65 years of age (Shear, Roose, Lenze, & Alexopoulos, 2005
). Incidence rates that include subsyndromal cases vary between 17.1 and 133.5 per 1,000 risk years (Meller, Fichter, & Schroppel, 1996
; Palsson, Ostling, & Skoog, 2001
), whereas rates of major depression and dysthymia range between 12.5 and 24.0 per 1,000 risk years (Forsell & Winblad, 1999
). Further, those with a history of late-life depression exhibit a doubling in risk for dementia (Jorm, 2001
). Some studies (Kessler, Foster, Webster, & House, 1992
; Palsson, et al.) but not all (Newmann, Engel, & Jensen, 1991
; Steffens et al., 2000
) have found that rates of depression steadily increase with age, after the age of 65 years. Geriatric depression increases overall public health burden by withdrawal of depressed individuals from social contacts, noncompliance in medication and other health care practices (Katrona, 1994
), and mortality (Rozzini, Frisoni, Sabatini, & Trabucchi, 2002
). Further, depression in later life is often underdiagnosed (Friedhoff, 1994
; Ginsberg, 2005
) and undertreated (Mulsant & Ganguli, 1999
). As the number of older people with psychiatric needs increases, the current health care system will face a great challenge in meeting the needs of this group (Bartels et al., 2002
).
Several factors have been shown to increase risk for new-onset depression in late life, including a prior history of depressive symptoms (Palsson et al., 2001
), female gender (Sonnenberg, Beekman, Deeg, & van Tilburg, 2000
), functional impairments (Cummings, Neff & Husaini, 2003
), and stressful life events (Shear et al., 2005
). Some researchers suggest that religious involvement may be associated with lower depression rates by means of the encouragement of coping strategies through spiritual, intellectual, and social avenues (Husaini, Blasi, & Miller, 1999
). Still other researchers have found no such effect in both cross-sectional studies (Courtenay, Poon, Martin, Clayton, & Johnson, 1992
; Spendlove, West, & Stanish, 1984
) and longitudinal studies (Bosworth, Park, McQuoid, Hays, & Steffens, 2003
; Braam, Beekman, Deeg, Smit, & van Tilburg, 1997
). Church attendance, one aspect of religious practice, helps connect individuals with their social network, conferring a sense of belonging that has been associated with reduction in depression risk in cross-sectional studies (Idler & Kasl, 1997
; Parker et al., 2003
) and longitudinal studies (Strawbridge, Shema, Cohen, & Kaplan, 2001
). Such participation, particularly at the end of life, can help bring about a sense of closure for events that were unexplainable and bring some meaning to the experience of physical and emotional pain (Koenig, Pargament, & Nielson, 1998
; Van Ness & Larson, 2002
). Religious involvement has been associated with a reduction in depression among functionally disabled (Idler & Kasl) and medically ill (Koenig, George, & Peterson, 1998
) older adults. Church attendance often encourages other more private religious behaviors, such as prayer, meditation, scripture reading, and caring for others' needs (Koenig, 1993
).
Methodological differences among the published studies on the association between religious involvement and late-life depression may explain the divergent findings. Most studies measure depression as a symptom count, whereas fewer use an approach based on the Diagnostic and Statistical Manual of Mental Disorders (DSM) to categorize major depression (Boey, 2003
). The majority of studies are also cross-sectional ones, precluding causal inference. Among longitudinal studies, typically researchers assess only current depression at each interview, ignoring additional depressive episodes with onset during the interval but that resolved prior to the follow-up interview. Further, the association between religious involvement and depression may be stronger in strongly religious communities where the influence of the doctrine pervades the lives of its members (Braam et al., 2001
). However, studies are very rare that examine this association in the cultural context of religiously homogeneous populations in which religious behavior may be more salient. Finally, we found no published studies that examined the association between religious practice and subsequent depressive episodes while statistically controlling for prior depression history, health, and functional status, all known to increase risk.
There is one such population-based study that provides an excellent opportunity to examine the effects of religious involvement, specifically church attendance, in a highly religious community, located in Cache County, Utah. Residents of Cache County suffer relatively lower rates of mortality before age 85. They have a conditional life expectancy for men at age 65 that, in the 1990 U.S. Census, was the highest in the country (Murray, Michaud, McKenna, & Marks, 1998
), exceeding national norms by almost 10 years (Manton, Stallard, & Tolley, 1991
). Older adult residents of this rural county in northern Utah are predominantly members of the Church of Jesus Christ of Latter-Day Saints (LDS; 92%), with more active members reported to have lower rates of mental health problems (Merrill & Salazar, 2002
). Some 76% of LDS members (vs 34% of non-LDS members) report church attendance at weekly or greater frequency (Norton, Skoog, Franklin, et al., 2006
). Strong LDS prohibitions against use of alcohol and tobacco may at least partially account for the greater longevity of Cache County residents. Additional explanations may include an agricultural past with high levels of activity in midlife and the absence of significant poverty as found also in the upper Midwest, which is another region whose residents show similarly high longevity (Murray et al.).
The prevalence of major depression among those aged 65 and older in this population has been previously reported as 4.3% in women and 3.0% in men (Steffens et al., 2000
). This is slightly higher than has typically been reported in North American studies using DSM criteria (Bland, Newman, & Orn, 1998
; Regier et al., 1993
), but it is much higher than the 1.4% in women and 0.4% in men in the NIMH Epidemiological Catchment Area Study (Koenig, Blazer & Sheikh, 1992
). Thus, the somewhat higher rates of depression among older residents in a highly religious community prompt investigation into the nature of the association between church attendance and depression risk in this population. Findings from such research may be informative for studies of late-life mental health in other communities with a predominant religious group.
We have previously reported results from the Cache County Study on Memory Health and Aging. In that community sample of 4,468 older adults, we found that regular church attendance was associated with a reduced prevalence of depression in women but increased prevalence in men, after we controlled for marital status, education, age, health and functional status, and religious affiliation (Norton, Skoog, Franklin, et al., 2006
). The study utilized a large community-based sample, without the selection bias typical of clinical studies (van Exel, Stek, Deeg, & Beekman, 2000
). It achieved an exceptionally high participation rate (90%); however, the study had a cross-sectional design.
We now present longitudinal data that ascertained depressive episodes during a 3-year interval after measurement of frequency of church attendance. Given the substantially increased risk for depression among older adults with a prior depression history (Norton, Skoog, Toone, et al., 2006
; Murphy et al., 2002
), we also sought to determine whether the effects of church attendance would be equivalent for those with and without a prior history of depression. We further hypothesized that the inverse association would be robust even after we statistically controlled for medical and functional status.
| METHODS |
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Interview Procedure
The dementia-ascertainment protocol included the following tests, which were conducted in the participant's home: a cognitive screening test, a semistructured clinical interview with a knowledgeable informant, and then, for those with possible dementia, an in-depth clinical assessment, conducted by nurse and psychometrician. Individuals with a working diagnosis of dementia were examined by a geropsychiatrist and underwent MRI scanning and standard laboratory tests for differential diagnosis. A panel of expert clinicians reviewed all available data and assigned final consensus diagnoses (Breitner et al., 1999
).
We obtained all measures from the baseline or follow-up interviews, except for social network, which we collected from a mail-in questionnaire (80% return rate). We obtained informed consent and all procedures received approval by the Institutional Review Boards of Utah State University, Duke University, and the Johns Hopkins University.
To improve data quality, we had a 10% sample of the interviews taped (with consent) and reviewed by the project's field supervisors. Quality Assurance specialists carefully checked responses for consistency and conformity to interview protocols, requiring interviewer clarification for potential errors or ambiguities. We had the data entered in duplicate, with cross-checks for accuracy.
Depression: Prior History at Initial Interview and Subsequent New Onset
A modified version of the NIMH Diagnostic Interview Schedule (DIS; Robins, Helzer, Croughan, & Ratcliff, 1981
; also see Helzer & Robins, 1988
) was completed at baseline and follow-up interviews. The DIS has been widely used in epidemiologic field studies and its psychometric properties have been well characterized (Helzer et al., 1985
; Murphy, 1995
). Psychometric properties of the DIS for lifetime mood disorders, comparing lay interviewers' and psychiatrists' ratings, has been shown to be
= 0.63, sensitivity = 80%, and specificity = 84% overall; sensitivity = 79% and specificity = 81% in current patients; and sensitivity = 82% and specificity = 67% in former patients (Robins et al.). Our modification included three gateway questions with the stem "in your lifetime, have you ever had a period of 2 weeks or more when, nearly every day you...," which was followed with three question stimuli: "felt sad, blue, or depressed," "lost all interest and pleasure in the things that you usually cared about or enjoyed," and "felt unusually cross or irritable" (Norton, 2001
; Steffens et al., 2000
). Participants endorsing at least one of these were also asked about appetite or weight change, sleep or concentration difficulties, restlessness, diminished energy level, guilt, or suicidal ideation. At baseline we asked for age of onset of first, most recent, and most severe episode. At follow-up we asked for symptoms and the onset and duration of each distinct episode in the interval.
Following the example of Blazer, Hughes, and George (1987)
and using DSM-IV criteria when possible (Steffens et al., 2000
), we diagnosed prior depressive episodes at baseline and each subsequent new-onset episode. We coded prior depression history as "major" if at least one episode included endorsement of five or more DIS symptoms including sadness or loss of interest, as "minor" if no prior episodes met this criterion, and as "none" if no prior episodes were reported. We coded new-onset major depression as positive if at least one episode in the 3-year follow-up interval met the aforementioned criterion for major depression (with onset after baseline interview date) and negative otherwise.
Church Attendance at Initial Interview
We coded frequency of attendance at religious services and activities as never, less than once per month, one or two times per month, weekly, and more than once per week. We also asked about religious affiliation, with available responses of Catholic, Protestant, LDS, Jewish, other, and no religion. There were 36 participants who indicated no religion, but frequency of church attendance was not queried for these individuals and because such information could not be inferred, we removed them from the sample. We dichotomized religious affiliation into LDS (92%) versus non-LDS.
Medical and Functional Status at Initial Interview
As the Cache County Study's focus was on dementia, the health status interview focused on vascular health conditions and events. For the present study, we utilized these data to create an indirect assessment of overall health status, calculated as the number of the following vascular health problems endorsed: stroke, transient ischemic attack, hypertension, hyperlipidemia, coronary bypass surgery, diabetes mellitus, and heart attack, myocardial infarction, or coronary thrombosis. The vascular health problems score ranged from 0 to 7 (M = 1.20, SD = 1.12). We coded functional impairment as the number of activities of daily living (ADLs) for which the participant reported needing assistance, including both basic and instrumental ADLs. The resulting ADL problems score ranged from 0 to 12 (M = 1.50, SD = 1.20). At initial interview, the number of current medications, another indicator of health (excluding all psychotropic medications), ranged from 0 to 20 (M = 4.82, SD = 3.32).
Demographics and Social Support at Initial Interview
We scored age and reported education as continuous measures, in years. We grouped the reported marital status into married, widowed, and separated or divorced. We measured social support from the mail-in questionnaire (completed immediately after baseline interview) according to the reported frequency of two types of contact—"getting together with family, friends or neighbors" and "attending meetings of social clubs, groups, or organizations such as bridge clubs, book clubs, hospital volunteers, gardening clubs, Rotary club, Kiwanis, and the VFW." We code each type of contact from 1 (rarely or never) to 6 (usually every day). We combined these two variables into a single measure—social contacts at least twice weekly—which was the median level of contact. This captured social involvement in excess of a single, possibly routine, activity occurring only weekly.
Statistical Analysis
We computed logistic regression models to test for the effect of church attendance on new-onset major depression, both before and after adjustment for other factors known to increase depression risk. To first reexamine the apparently higher depression rate among LDS members that we found in our cross-sectional study (Norton, Skoog, Franklin, et al., 2006
), we included religious affiliation (LDS vs non-LDS) in our initial model. Subsequent models added in frequency of church attendance (Model 2), gender (Model 3), marital status, education, age, health status (Model 4), and finally, prior depression history (Model 5). We computed odds ratios by using the fitted logistic regression model parameters, with corresponding 95% Wald confidence intervals. We computed all statistical analyses by using Statistical Package for the Social Sciences, version 13.0.
| RESULTS |
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Attrition
To examine potential attrition bias, we compared those individuals who remained in our final sample with those who dropped out as a result of death, refusal, moving away, or incident dementia. Longitudinal participants were more likely to be LDS members [
2(1, N = 4,473) = 6.08, p =.014], married [
2(2, N = 4,473) = 45.6, p <.001], younger by approximately 4 years [t(4471) = 18.6, p <.001], more highly educated by approximately 0.5 years [t(4471) = 5.2, p <.001], report higher frequency of church attendance [
2(4, N = 4,396) =121.8, p <.001], have approximately 0.8 fewer ADL problems [t(4471) = 12.6, p <.001], have approximately 0.2 fewer lifetime vascular health problems [t(4471) = 5.0, p <.001], and take approximately 0.5 fewer medications [t(4471) = 4.4, p <.001]. There was a trend for female participants to be more likely than male participants to participate at follow-up [
2(1, N = 4,473) = 3.29, p =.070], although this did not reach statistical significance. Prior depression history [
2(2, N = 4,473) = 3.92, p =.141] was not associated with longitudinal participation.
Bivariate Associations
The following categorical variables were significantly associated with major depression in simple bivariate analyses: gender, prior depression history, LDS church affiliation, and frequency of church attendance. However, marital status was not significantly associated with major depression (Table 1). Among the continuous variables that we examined, individuals who experienced major depression over the interval reported more ADL problems, more health problems, and were taking more nonpsychotropic medications at initial interview, compared with those who did not. Age and education level were not significantly related to major depression.
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We next determined that neither prior depression history nor LDS affiliation moderated the inverse association between church attendance and new-onset major depression (two-way interactions with church attendance: p =.951 and p =.693, respectively). Likewise, the three-way LDS Affiliation x Church Attendance x Prior Depression History interaction was nonsignificant (p =.830). We removed all nonsignificant interaction terms.
To explore social networks as a potential mediator, we reran the final model, adjusting for whether the participant reported at least twice weekly in-person social contacts with family or friends (model not shown). Odds ratios (ORs) for weekly church attendance dropped from OR = 0.66 to OR = 0.59 (95% confidence interval or CI = 0.33–1.07; value change from p =.067 to p =.081), and those for more-than-weekly church attendance increased from OR = 0.51 to OR = 0.54 (95% CI = 0.28–1.02; value change from p =.013 to p =.058), suggesting that at least some of the apparent effect of church attendance is mediated through social network contacts.
Figure 1 demonstrates the higher rates of new-onset major depression among LDS members and among those with a prior depression history, and lower rates among those with church attendance at least weekly. Further, Figure 1 illustrates the nonsignificant interaction effects such that more frequent church attendance is associated with lower new-onset major depression rates within each religious affiliation, and within prior depression history subgroups.
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| DISCUSSION |
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Church attendance more often than weekly is indicative of a higher level of engagement, including midweek participation in auxiliary organizations and volunteer church callings. Such activities enhance interpersonal attachments through an added exchange of affection, respect, sociability, and companionship between members than what may be afforded by lower levels of involvement (Duke, 1998
). Old age and disability often necessitate a shift in focus away from what one produces and accomplishes as the basis for self-worth, which are the typical basis in earlier adult life (Koenig, 1994
). Christian theology (including LDS) provides strong assurance that each individual has inherent value and worth, regardless of abilities (Sapp, 1987
). Furthermore, other theologies as well as nontheological value systems and ethical codes might encourage adherents to internalize similar beliefs that may reduce depression risk. These data provide some evidence that frequent reinforcement of these notions through high levels of religious participation, regardless of affiliation, may have a beneficial effect on the reduction in depression risk, even for those individuals with a prior history of depression.
New-onset major depression was about 1.6 times as frequent in women as in men, a common finding across many studies (Sonnenberg et al., 2000
), though this effect became nonsignificant after we controlled for prior depression history. Consistent with cross-sectional findings (Norton, Skoog, Franklin, et al., 2006
), we also found that participants with LDS affiliation reported twice as much new-onset major depression as their non-LDS counterparts, even after we controlled for all other variables. These results are in contrast to lower rates of mental health problems found among younger LDS (vs younger non-LDS) individuals (Judd, 1998
). One factor that may contribute to higher rates of depression among older LDS members is feeling guilt or inadequacy at not living up to high expectations for compliance with church doctrine and religious practices (Bergin, Stinchfield, Gaskin, Masters, & Sullivan, 1988
).
Older LDS individuals may also experience a more noticeable social role loss in late life as important positions of church leadership are dramatically curtailed, typically given to younger members of the congregation. Older adults who are not of the LDS faith might not have experienced such heavy involvement in organizational power within their respective churches and thus may not have experienced as dramatic a loss of important role(s) within the church upon reaching old age, particularly for men (Cnaan & Helzer, 2004
).
LDS individuals may also be somewhat more culturally conditioned to disclose psychological problems, given that they attend monthly testimony meetings where individuals publicly and extemporaneously bear testimony to their religious beliefs, and how these beliefs have helped them cope with life's adversities and make important decisions. "Feelings of profoundest concern are often expressed: appreciation of good family relationships, thanksgiving for blessings..." (Jolley, 1992
, p. 502). Through this sharing of very personal psychological feelings, those listening are able "to understand the message both intellectually and spiritually" (Christensen, 1992
, p. 1,471). It is speculated that this practice may translate to openness to discuss psychological problems with research interviewers, potentially resulting in apparently higher rates of depression among LDS individuals.
LDS doctrine teaches of an afterlife that includes a perfecting of physical and cognitive abilities, as well as the joy of eternal marriages and families. Thus, many older LDS individuals who feel a degree of worthlessness given their present limitations, and who also have many deceased loved ones, regularly question the purpose for their continued existence in mortality.
Another factor that may affect higher rates of new-onset major depression among LDS members is that non-LDS residents may be particularly resilient. The relatively small number of non-LDS individuals living in Cache County may likely have made a conscious choice to live in a pervasively LDS environment and may not require the levels of social support most people would find desirable. Conversely, LDS members who do not attend church may experience some degree of social isolation given that the community support structure revolves largely around church activity. Additionally, more active LDS churchgoers may be reluctant to try too hard to "reactivate" fellow adherents who have stopped attending church. Generalizability of these findings may therefore be somewhat limited in other religious groups.
Limitations
Because of the population-based nature of the study, depression was not assessed by physicians but by trained lay interviewers, and epidemiologic instruments for such large-scale fieldwork may have limits to psychometric stability (Regier et al., 1998
). Further, our use of a skip-out interview strategy with the DIS, though common in epidemiological research, has the potential for underdiagnosis, given that depression in late life can appear with a symptom profile that differs from that found in younger adults (Gallo & Rabins, 1999
). A study comparing the DIS and the psychiatrist-rated Schedules for Clinical Assessment in Neuropsychiatry revealed a bias toward underreporting (particularly in men), suggesting that associations with risk factors are likely to be conservative (Eaton, Neufeld, Chen, & Cai, 2000
).
Frequency of church attendance, though perhaps the most common metric used in studies of religiosity, is but a single aspect of a multidimensional construct (Judd, 1999
). Therefore, this study does not offer in-depth explanations for the inverse association with depression in this population. It remains unclear whether the effect has more to do with enhanced understanding of religious doctrine and sense of life purpose through religious study in a group setting, a sense of reconciliation with a higher power, or enhanced social contacts and support from fellow church members (Hoult, 1958
).
Although we included statistical controls for social network, health status, and functional limitations, there may be other potential confounders that we omitted as they were unavailable. Those persons who attend church more than once weekly may have higher levels of vitality or energy that allow them to engage in a wide range of activities (church, hobbies, community service). It is conceivable that the lower levels of depression at higher church attendance levels may be largely due to this greater overall vitality rather than church attendance alone.
Several variables were associated with nonresponse at follow-up which may have somewhat biased our results, most notably church affiliation, frequency of church attendance, and marital status. Because our longitudinal sample had a slightly higher proportion of married LDS individuals with high church attendance, compared with our baseline sample, we probably had reduced statistical power to detect associations. However, the strongest predictor of new-onset major depression–prior depression history—was not related to attrition.
The inverse association between church attendance and major depression reported previously in women (Norton, Skoog, Franklin, et al., 2006
) was again found in the present longitudinal study. However, the opposite finding of higher rates of depression among men who attended church more often was no longer apparent with longitudinal follow-up. Although not enough for a significant interaction, the effects were somewhat stronger for women who exhibited a 40% and 54% reduction in depression risk for those at weekly and greater-than-weekly levels of attendance, respectively, relative to depression rates for women attending less often than weekly. Corresponding reductions in risk for men were 25% and 43%, respectively. Additionally, men were more likely to drop out than women, both in general and at higher baseline church attendance levels. This nonrandom attrition may have affected our results (data not shown).
As we already mentioned, these findings may not generalize to all populations of older adults but may be applicable to other populations with a predominant religious group. Although LDS theology includes some unique doctrines, it has many other theological aspects common to other religious groups that may have equal salience in the individual lives of its members. Members of other highly religious communities may exhibit similar cultural influences that place a high value on the application of spiritual coping to life's challenges, successful marriages, and parenting that could place their members at similar risk for depression when such ideals are unmet in the lives of individual members. Generalizability of this predominantly LDS population is enhanced by national studies reporting that LDS members have average socioeconomic status and similar overall happiness, marital happiness, and self-esteem (Heaton, Goodman, & Holman, 1994
), and on average "flat" (normal) personality profiles on the Minnesota Multiphasic Personality Inventory (Judd, 1998
).
Conclusions
The present study is our second report in a series of studies addressing the association between church attendance and new-onset major depression among members of the Cache County Study cohort, a group exhibiting high levels of church attendance (Norton, Skoog, Franklin, et al., 2006
). Noted strengths are that it is a population-based study with a 90% participation rate at in-person interview, conferring significant protection against response bias (Norton, Breitner, Welsh, & Wyse, 1994
). Further, our models controlled for potential confounding factors of physical health, functional abilities, marital status, and education. We found rates of new-onset major depression to be twice as high among LDS participants as among non-LDS participants. Further, we established a significant inverse association between frequency of church attendance and new-onset major depression, even net of the effect of the highly predictive risk factor of prior depression history.
Church attendance often encourages private religious behaviors such as prayer, meditation, and scripture reading, as well as public behaviors such as volunteerism (Koenig, 1993
). Future studies could expand on the present work by examining these as potential mediators in the church attendance–depression association and the extent to which the effect of these behaviors may be moderated by gender (whereas church attendance was not). The extent to which particular aspects of church attendance may differentially moderate the effect of stressful life events should also be studied.
| Acknowledgments |
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We thank the study participants and their families for their generosity in willingness to participate. We also thank Drs. Chiadi Onyike, Curt Canning, and Ronald Munger for their careful reviews of the manuscript. Other Cache County Study investigators involved in the project are as follows (in alphabetic order): James Anthony, PhD; Erin Bigler, PhD; Ron Brookmeyer, PhD; James Burke, MD, MPH; Michelle Carlson, PhD; Eric Christopher, MD; Jane Gagliardi, MD; Robert Green, MD; Andrea Hart, PhD; Kate Hayden, PhD; Christine Hulette, MD; Liz Klein, MPH; Carol Leslie, MA; Constantine Lyketsos, MD, MHS; Richard A. Miech, PhD; John Morris, MD; Ronald Munger, PhD; Chiadi Onyike, MD; Truls Østbye, MD, PhD; Ron Petersen, MD; Roxane Pfister, MS; Carl Pieper, PhD; Kathy Piercy, PhD; Brenda Plassman, PhD; Peter Rabins, MD; Pritham Raj, MD; Russell Ray, MS; Linda Sanders, MPH; Martin Steinberg, MD; Marty Toohill, PhD; Leslie Toone, MS; Jeannette J. Townsend, MD; Heidi Wengreen, PhD; Nancy West, PhD; Michael Williams, MD; and Bonita W. Wyse, PhD.
| Footnotes |
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Received for publication November 15, 2006. Accepted for publication September 7, 2007.
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