Department of Psychiatry, St George's Hospital Medical School, London
Correspondence: Dr Sarah Clement, Department of Psychiatry, St George's Hospital Medical School, Cranmer Terrace, London SW17 ORE, UK. E-mail: s.clement{at}sghms.ac.uk
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Aims The primary aim is to compare levels of research activity in bipolar disorder and schizophrenia. Secondary aims are to examine how research activity on the disorders varies over time and across scientific fields.
Method The numbers of publications, projects, journals and funding awards on bipolar disorder and schizophrenia were extracted from nine computer databases to compare research activity on the two conditions.
Results Ratios (bipolar disorder: schizophrenia) ranged from 1:1.3 for the number of research funding awards to 1:7.6 for the number of clinical trials.
Conclusions There is a relative dearth of research activity on bipolar disorder compared with schizophrenia.
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
![]() |
AIMS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
![]() |
METHOD |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
Searching took place in March 2002. For the literature-searching databases, the period searched began at the databases' earliest year and ended at the year 2000, the most recent year for which complete data were available. For the other databases, the complete data-set was searched. The search strategies used were chosen on the advice of an information specialist. Searching under medical subject heading was conducted in four of the databases (Medline, EMBASE, PsycINFO and CINAHL). This type of searching draws together under one heading publications that may have used many different terms for a subject. It was not used in the Cochrane searches because, at the time of searching, the database had a backlog in attaching these headings, and pre-testing showed that searching under medical subject heading would have missed systematic reviews on bipolar disorder. Similarly, medical subject headings were not used for the National Research Register search because it has the same search system as the Cochrane Library. None of the other databases had the facility for searching under medical subject heading, therefore textword searching was used. The focus option was used for all databases that had it, to restrict the searches to publications that focused on the illnesses in question. No restriction was placed on the type of publication in the literature-searching databases. When it was available, the explode function was used, to ensure that relevant sub-categories of disease were included. The search strategies used are shown in Table 1.
In addition, one database, Medline, was used to examine changes over time and differences across scientific fields within bipolar disorder and schizophrenia research. Using the Medline search strategy shown in Table 1, comparisons were made between the number of bipolar and schizophrenia publications over 5-year periods between 1966 and 2000. To investigate differences across scientific fields, the 12 Medline subheadings with the highest numbers of publications within them for bipolar disorder and schizophrenia were examined.
Analysis
The extent of any disparity between levels of research activity for bipolar
disorder and schizophrenia was demonstrated by presenting the numbers of
publications/projects/journals/funding awards for the two conditions in ratio
format (bipolar disorder:schizophrenia, factored down).
In the analysis of Medline data on changes over time and across scientific
fields, 2 tests were undertaken. To examine where any
differences lay, Pearson residuals were produced (Hosmer & Lemeshow, 2000)
and those exceeding ±1.96 (the critical Z-value for the 5% significance
level) were considered significant.
![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
The investigation into the number of publications on bipolar disorder and
schizophrenia during 5-year periods between 1966 and 2000 showed that the
bipolar:schizophrenia ratio of publications varied from 1:2.6 in the 1980s to
1:5.0 in the late 1960s (see Table
3). There was a significant relationship between the type of
disorder the publication was about and the time period
(2=236.82, P < 0.0001). Examination of the Pearson
residuals suggests a U-shaped pattern, with bipolar disorder publications
being most underrepresented between 1966 and 1975, and again between 1991 and
1995, and least underrepresented between 1981 and 1990. The absolute
difference in the number of bipolar disorder and schizophrenia publications in
the most recent time period examined (1996-2000) was over twice that in the
earliest time period (1966-1970).
|
Investigation of the number of bipolar disorder and schizophrenia
publications under the 12 main Medline subheadings indicated that the
disparity was much greater in some scientific fields than in others
(2=2087.07, P < 0.0001) (see
Table 4). Examination of the
Pearson residuals revealed that disparities were significant for 9 of the 12
scientific fields. The areas where the residuals indicated that bipolar
disorder was most underrepresented were rehabilitation (with a 27-fold
relative excess of schizophrenia publications), psychology (with a 11-fold
relative excess) and pathology (with a 10-fold relative excess).
|
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
It is important to consider the following limitations of this study. Textword searching was the only form of searching possible on some of the databases. This may have resulted in relevant items being missed or irrelevant ones being included. Where searching under medical subject heading was used, indexing errors may have distorted the findings. In EMBASE, the lack of a bipolar disorder subject heading and the inclusion of psychotic depression in the manicdepressive psychosis subject heading may have distorted the findings, although, if so, it would have been in the direction of overestimating the number of bipolar disorder publications. Searching encompassed all types of publications, including non-empirical ones. Not all relevant journals are covered by the databases searched. Finally, the Journal Citation Reports database includes only journals old enough to have an impact factor, and so misses newer journals such as Bipolar Disorders (1999present).
The existing literature in this area has used two main indicators of research activity: the extent of research funding and literature size. We found no studies that have directly compared levels of research funding for bipolar disorder and schizophrenia. Pincus & Fine (1992) examined research funding for mental illness and addictive disorders and found that, although these conditions accounted for 12% of total health costs, they received only 4.7% of health research support. We found one study that included a comparison of the literature size on bipolar disorder and schizophrenia (Sprock & Hermann, 2000). This study was confined to one database, PsycLIT, and contained 1160 papers on bipolar disorder compared with 10 722 on schizophrenia over a 7-year period. Two studies have compared the number of papers on leading psychiatric disorders, but neither included a bipolar disorder category (Pincus et al, 1993; Morlino et al, 1997).
What might explain this disparity in research between bipolar disorder and schizophrenia? It has been proposed that illnesses with strong advocates or special interest groups (Gross et al, 1999; Sprock & Hermann, 2000), fashionable or rare illnesses (Al-Shahi et al, 2001), illnesses with high media or social prominence or those that present a high intellectual challenge (Sprock & Hermann, 2000) tend to be researched more. However, none of the above factors is an obvious explanation for the lack of research on bipolar disorder relative to schizophrenia.
Some of the disparity is likely to result from schizophrenia's greater overall disease burden, evident in higher hospitalisation rates (Craig et al, 2000), poorer global functioning (Grossman et al, 1991) and greater economic costs (Das Gupta & Guest, 2002). Clinicians seeing these day-to-day, highly visible aspects of burden may rightly wish to pursue research to combat such a debilitating illness. Types of burden for which bipolar disorder is worse than schizophrenia, such as suicide (Harris & Barraclough, 1997), excess mortality (Harris & Barraclough, 1998) and global burden (Murray & Lopez, 1997), are rarer events or are remote and secondary consequences. This may lower clinicians' perceptions of the seriousness of bipolar disorder, and make it less attractive as a subject for research.
A number of other factors might account for the disparity. Because lithium is a natural substance that cannot be patented, there may be less commercial interest to stimulate research. Our findings provide little support for this hypothesis, because the bipolar disorder:schizophrenia ratio for drug therapy publications on Medline was one of the lowest, at 1:2.3. Another possibility is that bipolar disorder is inherently more difficult to research, owing to the complexity that its episodic nature brings to research design (Calabrese et al, 2001). This cyclicity also may bring recruitment difficulties, with patients too unwell to participate when acutely ill and reluctant to be involved when well. The greater functional impairment of those with schizophrenia makes them a captive population in hospitals and day centres, easily accessible for recruitment into research studies.
The introduction of new research tools, such as neuroimaging, may be an important factor directing research activity (Morlino et al, 1997; Moncrieff & Crawford, 2001). Neuroimaging findings have been somewhat inconsistent in bipolar disorder (Strakowski et al, 2000). The more consistent schizophrenia findings are likely to have spurred on further neuroimaging research. This speculation is supported by our finding that Medline publications on pathology and physiopathology have the third and fourth highest disparity between schizophrenia and bipolar disorder.
Scientific opportunity is another postulated reason for disparities in research (Gross et al, 1999). Scientific opportunities often flow from theoretical models. Schizophrenia has attracted intense and long-standing interest, and several family, social and psychological models of aetiology and relapse precipitation have been hypothesised. Research into some of these hypotheses has, in turn, led to the development of evidence-based psychosocial interventions. Psychosocial models in bipolar disorder are fewer and of more recent origin (e.g. Scott, 2001). This notion is supported by our finding that the scientific area with the second highest disparity was psychology. Treatment breakthroughs also have been proposed as a factor influencing research activity, with a surge in schizophrenia research being noted after the introduction of new psychotropic drugs (Moncrieff & Crawford, 2001).
The development of theoretical models, the emergence of treatment breakthroughs and the overall levels of research activity may be a reflection of the degree of interest that an illness holds for researchers. Depression and the non-psychotic aspects of mania are, to some degree, extensions of normal human experience, whereas psychosis cannot be placed easily on that spectrum. Perhaps the other-worldliness of psychosis holds a fascination for researchers and attracts them to schizophrenia rather than to bipolar disorder, with its more prosaic depression and its less prevalent psychosis. One final possibility is that, by straddling the areas of psychosis (where schizophrenia is the dominant paradigm) and affective disorder (where depression is the dominant paradigm), bipolar disorder has no natural home from which to develop as a research speciality.
It is tempting to speculate whether the comparative dearth of research activity on bipolar disorder also reflects a wider clinical neglect of the condition. Bipolar disorder has received no specific consideration in the UK National Service Framework for Mental Health (Morriss et al, 2002). New resources are being allocated to early intervention in psychosis (Department of Health, 2001), and these services will be geared mostly towards managing young people with schizophrenia. Nationally there are very few specialist services for bipolar disorder. The lack of research in bipolar disorder, therefore, may be intertwined with the level of clinical interest in the condition, and an innovation or breakthrough in one sphere may spur activity in the other.
![]() |
Clinical Implications and Limitations |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
LIMITATIONS
![]() |
ACKNOWLEDGMENTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Calabrese, J. R., Rapport, D. J., Shelton, M. D., et al
(2001) Evolving methodologies in bipolar disorder maintenance
research. British Journal of Psychiatry,
178 (suppl. 41),
s157-s163.
Craig, T. J., Bromet, E. J., Fenning, S., et al
(2000) Is there an association between duration of untreated
psychosis and 24-month clinical outcome in a first-admission series?
American Journal of Psychiatry,
157, 60-66.
Das Gupta, R. & Guest, J. F. (2002) Annual
cost of bipolar disorder to UK society. British Journal of
Psychiatry, 180,
227-233.
Department of Health (2001) The Mental Health Policy Implementation Guide. London: Department of Health.
Goodwin, G. (2000) Perspectives for clinical research on bipolar disorders in the new millennium. Bipolar Disorders, 2, 302-303.[CrossRef][Medline]
Gross, C. P., Anderson, G. F. & Rowe, N. R.
(1999) The relation between funding by the National
Institutes of Health and the burden of disease. New England Journal
of Medicine, 340,
1881-1887.
Grossman, L. S., Harrow, M., Goldberg, J., et al (1991) Outcome of schizoaffective disorder and two long-term follow-ups: comparisons with outcome of schizophrenia and affective disorders. American Journal of Psychiatry, 148, 1359-1365.[Abstract]
Harris, E. C. & Barraclough, B. (1997) Suicide as an outcome for mental disorders. A meta-analysis. British Journal of Psychiatry, 170, 205-228.[Abstract]
Harris, E. C. & Barraclough, B. (1998) Excess mortality of mental disorder. British Journal of Psychiatry, 173, 11-53.[Abstract]
Moncrieff, J. & Crawford, M. J. (2001) British psychiatry in the 20th century: observations from a psychiatric journal. Social Science and Medicine, 53, 349-356.[CrossRef][Medline]
Morlino, M., Lisanti, F., Gogliettino, A., et al (1997) Publication trends of papers on schizophrenia. A 15-year analysis of three general psychiatric journals. British Journal of Psychiatry, 171, 452-456.[Abstract]
Morriss, R., Marshall, M. & Harris, A.
(2002) Bipolar affective disorder: left out in the cold.
BMJ, 324,
61-62.
Murray, J. L. & Lopez, A. D. (1997) Global mortality, disability, and the contribution of risk factors: Global Burden of Disease Study. Lancet, 349, 1436-1442.[CrossRef][Medline]
Pincus, H. A. & Fine, T. (1992) The anatomy of research funding of mental illness and addictive disorders. Archives of General Psychiatry, 49, 573-579.[Abstract]
Pincus, H. A., Henderson, B., Blackwood, D., et al (1993) Trends in research in two general psychiatric journals in 1969-1990: research on research. American Journal of Psychiatry, 150, 135-142.[Abstract]
Scott, J. (2001) Cognitive therapy as an
adjunct to medication in bipolar disorder. British Journal of
Psychiatry, 178 (suppl.),
s164-s168.
Sprock, J. & Hermann, D. (2000) Relative size of the literatures for psychopathological disorders: numbers of articles pertaining to DSMIV Diagnostic Categories. Journal of Clinical Psychology, 56, 491-504.[CrossRef][Medline]
Strakowski, S. M., DelBello, M. P., Alder, C., et al (2000) Neuroimaging in bipolar disorder. Bipolar Disorders, 2, 148-164.[CrossRef][Medline]
Received for publication April 23, 2002. Revision received September 27, 2002. Accepted for publication October 10, 2002.
Related articles in BJP: