THE ICEBERG REVISITED 22
References 1 2
3 4 5 6 7 8 9 10 11 12 13
15 16 17 18 19 20 21
23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42
McAlpine SG, Douglas AS, Robb RA. Brit. Med. J. 1957l;ii:983. Ministry of Health. On the State of the Public Health. H.M. Stationery Office, 1960. Boyes DA, Fidler HK, Lock DR. Brit. Med J 1962;i:203. Royal College of Physicians. Smoking and Health. London, 1962. Dawber TR. Proc. R. Soc. Med. 1962;55:265. Criminal Statistics 1960. H.M. Stationery Office, 1961. Lancet. 1962:p1171. Annual Abstract of Statistics. H.M. Stationery Office, 1961: no. 98. Townsend P. Bull. World Hlth. Org. 1959;21:583. Illsley R, Thompson B. Sociol. Review 1961;9:27. Philp AF, Timms N. Problem of the Problem Family. London, 1957. Lancet. 1962;i:1169. Tietze C. Amer. J Obstet. Gynec. 1948;56:1160. Registrar General. Supplement on Mental Health 1960. H.M. Stationery Office, 1961. Registrar General. Report on the Hospital Inpatient Inquiry, 1956-57. H.M. Stationery Office, 1961. Road Research 1960. H.M. Stationery Office, 1961. Kagan A, Dawber TR, Kannel WB, Revotskie N. Fed Proc. 1962;21 (suppl. 11):52. Social Medicine Research Unit (M.R.C.). Unpublished data. Morris JN, Crawford MD. Brit Med J. 1958;ii:1485. Metropolitan Life Insurance Company. Statistical Bulletin, January 1960, p4. Hill Kr, Camps FE, Rigg K, McKinney BEG. Brit Med J. 1961;i: 1190.
Published by Oxford University Press on behalf of the International Epidemiological Association ß The Author 2013; all rights reserved.
International Journal of Epidemiology 2013;42:1613–1615 doi:10.1093/ije/dyt112
Commentary: The iceberg revisited John M Last Department of Epidemiology and Community Medicine, University of Ottawa, 451 Smyth Road, Ottawa, Ontario K1H 8M5, Canada. E-mail: [email protected]
Accepted
16 May 2013
The epidemiological concept of the ‘iceberg’ of disease1—what is visible and what lurks below the surface—has been durable and useful. As of September 2012, the paper had been cited 1380 times2 and as the figure shows, citations associated with directly relevant papers have remained remarkably steady for 50 years. The metaphor of the iceberg is a valuable communications aid, immediately grasped by everyone. It is relevant to surveillance, measurement of population
health, measuring the burden of illness, screening, needs assessment, health services planning and much else, for instance understanding selection bias. It clarifies the relationship between clinical epidemiology (which deals only with the visible part) and population-based epidemiology. My paper grew from a germ of the idea when I was a visiting fellow from Australia, spending a mindexpanding year mentored by J.N. (‘Jerry’) Morris in the MRC Social Medicine Research Unit, located in
Downloaded from http://ije.oxfordjournals.org/ by guest on June 15, 2015
14
Ministry of Health. The Health and Welfare Services. H.M. Stationery Office, 1961. Registrar General. Statistical Review of England and Wales, 1960, part 1, tables, medical. H.M. Stationery Office, 1961. College of General Practitioners. 1961 ibid. ii,973. College of General Practitioners. 1962 ibid i, 1497. David WD. US publ. Hlth. Serv. Publ. No. 666, Washington DC, 1959. Heasman MA. Stud. Med. Popul. Subj. 1961; No.17. Kass EH. Ann. Intern. Med 1962;56:46. Kessel WIN. Brit. J prev. Soc Med. 1960;14:16. Kilpatrick GS. Brit. Med. J. 1961;ii:1736. Lawrence JS, Laine VAI, de Graaff R. Proc. Roy. Soc. Med. 1961;54:454. Logan WPD, Cushion AA. Morbidity Statistics from General Practice. HM Stationery Office, 1958. Miall WE, Oldham PD. Clin. Sci. 1958;17:409. Munch-Petersen E. Bull. World Hlth Org. 1961;24:761. Pond DA, Bidwell BH, Stein L. Psychiat. Neurol. Neurochir. 1960;63:217. Walker JB, Kerridge D. Diabetes in an English Community, Leicester, 1961. Wilson JMG. Monthly Bull. Min. Hlth PHLS 1961;20:214. Morris JN. Uses of Epidemiology, Edinburgh, 1957. Ministry of Health. On the State of the Public Health. H.M. Stationery Office, 1961. Simmons NA, Williams JD. Lancet 1962;i:1377. Smith LG, Schmidt J. J. Amer. Med. Ass. 1962;181: 431. Semmence A. Brit. Med. J 11959;ii:1153.
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INTERNATIONAL JOURNAL OF EPIDEMIOLOGY
clinically and could be detected earlier in their natural course by screening questionnaires. Perhaps some forms where early intervention might be beneficial could be differentiated. We need to distinguish bipolar disorder that often responds to medication but can be life-threatening without treatment, from adolescent angst and ‘reactive’ depression associated with bereavement, loss of job, etc. Alzheimer’s disease—dementia that often begins comparatively early in middle age with pathognomonic histopathology—differs from other forms of dementia with onset usually later in life, secondary to cerebral vascular disease, repeated head injuries, chemical poisoning etc. Some of these conditions are preventable or amenable to treatment if detected early, others not so much at the present state of medical knowledge.5 After the paper was published, I was invited to speak on the concept in university departments and community clinics all around the USA where I lived for a year soon afterwards. At that time, perhaps because of the company I kept, there was considerable emphasis on use of the ‘iceberg’ concept to evaluate the quality of medical care, by comparing numbers of observed cases at specified disease stages with the numbers expected according to theoretical models. Of course it is essential when comparing ‘observed’ and ‘expected’ numbers to bear in mind wide confidence limits and selective factors that might influence a particular clinic’s population. One methodological detail bothered me occasionally. When I was asked whether the numbers in the key table in the paper were based on incidence or prevalence data, I gave an evasive answer or just said ‘yes’—they were based on incidence or prevalence data. This may be a slightly messy flaw in the methods I used to derive the numbers of conditions or cases of particular diseases that might be expected to be present or to arise over the course of a year in a hypothetical ‘average’ general practice, or a clinic’s population. At a pragmatic
6
5
4
3
2
0
1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012
1
Figure 1 Number of publications referring to ‘The Iceberg’, 1963–2012 Source: http://apps.webofknowledge.com/CitationReport.do?product¼WOS&search_mode¼CitationReport&SID¼2DFD2DF EM6C@n2L@FmI&page¼1&cr_pqid¼6&viewType¼summary (14 February 2013, date last accessed)
Downloaded from http://ije.oxfordjournals.org/ by guest on June 15, 2015
those days in an office and laboratory building behind the London Hospital Medical College. Jerry taught me a great deal of epidemiology by engaging me in revision of data for a second edition of his wonderful little book Uses of Epidemiology.3 There was a table in the first edition on ‘Completing the clinical picture’— demonstrating variation of the observed numbers affected by particular conditions according to the method of observation and the stage of the disease at which observations are made. It occurred to me as a former general practitioner that the numbers in this table would have considerable dramatic impact if they were projected onto the population of an ‘average’ general practice. There is greatest interest in the submerged part of the iceberg—disease precursors, preclinical conditions and very early clinical stages, that if identified and appropriate interventions initiated, might nip in the bud an otherwise relentlessly progressive and ultimately lethal disease process. This has become an integral part of teaching in family medicine programmes and other front-line aspects of health care. In the 50 years since the paper was published, great progress has been made in many aspects of clinical medicine, notably screening tests, diagnostic imaging, genomics and methods of detecting and managing inborn errors of metabolism. We can map the genome of apparently healthy people who will eventually develop Huntington’s disease, and girls and women at unusually high risk of developing aggressive breast cancer. Challenging philosophical and ethical problems have arisen since the health care system became capable of detecting precursors and early stages of these and other dangerous and often fatal conditions.4 The concept has been applied to examine the natural history of many conditions and suggest early diagnostic interventions. Consider depression and dementia. Incipient forms may be poorly defined
LAST AND ICEBERGS – SPOTTING THE ICEBERG DOESN’T PREDICT ITS SCALE
identified the concept ever since: ‘The iceberg’. We are all in his debt for this: my title was cumbersome and forgettable, whereas the vivid metaphor of the iceberg has proved to be memorable and appropriate.
Acknowledgement I am grateful to Natalia Abraham, Karen Trollope Kumar, Ian McDowell and Bob Spasoff for help with this paper. Conflict of interest: None declared.
References 1
2
3 4
5
Last JM. The Iceberg: ‘Completing the clinical picture’ in general practice. Lancet 1963;2:28–31. Reprinted Int J Epidemiol 2013; doi:10.1093/ije/dyt113. Web of Knowledge. Science Citation Index data, available at http://apps.webofknowledge.com/CitationReport.do? product¼WOS&search_mode¼CitationReport&SID¼ 2DFD2DFEM6C@n2L@FmI&page¼1&cr_pqid¼6& viewType¼summary (24 June 2013, date last accessed). Morris JN. Uses of Epidemiology. Edinburgh and London: E & S Livingstone, 1957. European Society of Human Genetics. Population genetic screening programmes: technical, social and ethical issues. Recommendations. Eur J Hum Genet 2003; 11(Suppl 2):S5–S7. See http://www.mayoclinic.com/health/dementia/DS01131 /DSECTION¼tests-and-diagnosis (14 February 2013, date last accessed) for description and critique of diagnostic methods for identifying dementia.
Published by Oxford University Press on behalf of the International Epidemiological Association ß The Author 2013; all rights reserved.
International Journal of Epidemiology 2013;42:1615–1617 doi:10.1093/ije/dyt123
Commentary: Last and Icebergs – spotting the iceberg doesn’t predict its scale, even after 50 years FD Richard Hobbs Department of Primary Care Health Sciences, New Radcliffe House, Walton Road, Oxford University, Oxford, UK. E-mail: [email protected]
Accepted
13 February 2013
Estimating the total disposition and magnitude of one’s adversaries compared with to what is readily
visible is a standard military prerequisite for tactics, which bears scrutiny as an option for delivering
Downloaded from http://ije.oxfordjournals.org/ by guest on June 15, 2015
level, I don’t think it matters much. It’s the concept that matters, not precise numbers of specified conditions. Another perspective on the ‘iceberg’ concept arose in discussions at community clinics and prepaid health care programmes. Administrators and managers suggested that the numbers of ‘expected’ cases of certain conditions could be compared with the numbers observed over a period of years, thereby providing a measuring instrument to evaluate the efficacy of screening procedures and routine clinical examination of patients. Although this might be possible, I would be cautious about suggesting use of the numbers from a theoretical model in any practical setting. Even the numbers from a large database such as the population of a prepaid health care plan covering many millions, as in California and the New England states, are subject to selection bias and random variation. I doubt whether valid conclusions could be based on comparison of 1 year’s experience in such a population with another, or comparison of clinic populations in different countries or regions. Such comparisons would be interesting, and some useful inferences might be derived from them but not to evaluate the efficacy of screening procedures or clinical care. After Jerry Morris had reviewed and approved my final text without suggesting any further changes, I sent it to Sir Theodore (‘Robbie’) Fox, the eminent editor of the Lancet. He accepted it without changing the text in any way, but did make one important modification. My title was ‘Completing the clinical picture in general practice’. Robbie Fox made that a subtitle and added as the title the word that has
1615
References 1 2
3 4 5 6 7 8 9 10 11 12 13
15 16 17 18 19 20 21
23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42
McAlpine SG, Douglas AS, Robb RA. Brit. Med. J. 1957l;ii:983. Ministry of Health. On the State of the Public Health. H.M. Stationery Office, 1960. Boyes DA, Fidler HK, Lock DR. Brit. Med J 1962;i:203. Royal College of Physicians. Smoking and Health. London, 1962. Dawber TR. Proc. R. Soc. Med. 1962;55:265. Criminal Statistics 1960. H.M. Stationery Office, 1961. Lancet. 1962:p1171. Annual Abstract of Statistics. H.M. Stationery Office, 1961: no. 98. Townsend P. Bull. World Hlth. Org. 1959;21:583. Illsley R, Thompson B. Sociol. Review 1961;9:27. Philp AF, Timms N. Problem of the Problem Family. London, 1957. Lancet. 1962;i:1169. Tietze C. Amer. J Obstet. Gynec. 1948;56:1160. Registrar General. Supplement on Mental Health 1960. H.M. Stationery Office, 1961. Registrar General. Report on the Hospital Inpatient Inquiry, 1956-57. H.M. Stationery Office, 1961. Road Research 1960. H.M. Stationery Office, 1961. Kagan A, Dawber TR, Kannel WB, Revotskie N. Fed Proc. 1962;21 (suppl. 11):52. Social Medicine Research Unit (M.R.C.). Unpublished data. Morris JN, Crawford MD. Brit Med J. 1958;ii:1485. Metropolitan Life Insurance Company. Statistical Bulletin, January 1960, p4. Hill Kr, Camps FE, Rigg K, McKinney BEG. Brit Med J. 1961;i: 1190.
Published by Oxford University Press on behalf of the International Epidemiological Association ß The Author 2013; all rights reserved.
International Journal of Epidemiology 2013;42:1613–1615 doi:10.1093/ije/dyt112
Commentary: The iceberg revisited John M Last Department of Epidemiology and Community Medicine, University of Ottawa, 451 Smyth Road, Ottawa, Ontario K1H 8M5, Canada. E-mail: [email protected]
Accepted
16 May 2013
The epidemiological concept of the ‘iceberg’ of disease1—what is visible and what lurks below the surface—has been durable and useful. As of September 2012, the paper had been cited 1380 times2 and as the figure shows, citations associated with directly relevant papers have remained remarkably steady for 50 years. The metaphor of the iceberg is a valuable communications aid, immediately grasped by everyone. It is relevant to surveillance, measurement of population
health, measuring the burden of illness, screening, needs assessment, health services planning and much else, for instance understanding selection bias. It clarifies the relationship between clinical epidemiology (which deals only with the visible part) and population-based epidemiology. My paper grew from a germ of the idea when I was a visiting fellow from Australia, spending a mindexpanding year mentored by J.N. (‘Jerry’) Morris in the MRC Social Medicine Research Unit, located in
Downloaded from http://ije.oxfordjournals.org/ by guest on June 15, 2015
14
Ministry of Health. The Health and Welfare Services. H.M. Stationery Office, 1961. Registrar General. Statistical Review of England and Wales, 1960, part 1, tables, medical. H.M. Stationery Office, 1961. College of General Practitioners. 1961 ibid. ii,973. College of General Practitioners. 1962 ibid i, 1497. David WD. US publ. Hlth. Serv. Publ. No. 666, Washington DC, 1959. Heasman MA. Stud. Med. Popul. Subj. 1961; No.17. Kass EH. Ann. Intern. Med 1962;56:46. Kessel WIN. Brit. J prev. Soc Med. 1960;14:16. Kilpatrick GS. Brit. Med. J. 1961;ii:1736. Lawrence JS, Laine VAI, de Graaff R. Proc. Roy. Soc. Med. 1961;54:454. Logan WPD, Cushion AA. Morbidity Statistics from General Practice. HM Stationery Office, 1958. Miall WE, Oldham PD. Clin. Sci. 1958;17:409. Munch-Petersen E. Bull. World Hlth Org. 1961;24:761. Pond DA, Bidwell BH, Stein L. Psychiat. Neurol. Neurochir. 1960;63:217. Walker JB, Kerridge D. Diabetes in an English Community, Leicester, 1961. Wilson JMG. Monthly Bull. Min. Hlth PHLS 1961;20:214. Morris JN. Uses of Epidemiology, Edinburgh, 1957. Ministry of Health. On the State of the Public Health. H.M. Stationery Office, 1961. Simmons NA, Williams JD. Lancet 1962;i:1377. Smith LG, Schmidt J. J. Amer. Med. Ass. 1962;181: 431. Semmence A. Brit. Med. J 11959;ii:1153.
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INTERNATIONAL JOURNAL OF EPIDEMIOLOGY
clinically and could be detected earlier in their natural course by screening questionnaires. Perhaps some forms where early intervention might be beneficial could be differentiated. We need to distinguish bipolar disorder that often responds to medication but can be life-threatening without treatment, from adolescent angst and ‘reactive’ depression associated with bereavement, loss of job, etc. Alzheimer’s disease—dementia that often begins comparatively early in middle age with pathognomonic histopathology—differs from other forms of dementia with onset usually later in life, secondary to cerebral vascular disease, repeated head injuries, chemical poisoning etc. Some of these conditions are preventable or amenable to treatment if detected early, others not so much at the present state of medical knowledge.5 After the paper was published, I was invited to speak on the concept in university departments and community clinics all around the USA where I lived for a year soon afterwards. At that time, perhaps because of the company I kept, there was considerable emphasis on use of the ‘iceberg’ concept to evaluate the quality of medical care, by comparing numbers of observed cases at specified disease stages with the numbers expected according to theoretical models. Of course it is essential when comparing ‘observed’ and ‘expected’ numbers to bear in mind wide confidence limits and selective factors that might influence a particular clinic’s population. One methodological detail bothered me occasionally. When I was asked whether the numbers in the key table in the paper were based on incidence or prevalence data, I gave an evasive answer or just said ‘yes’—they were based on incidence or prevalence data. This may be a slightly messy flaw in the methods I used to derive the numbers of conditions or cases of particular diseases that might be expected to be present or to arise over the course of a year in a hypothetical ‘average’ general practice, or a clinic’s population. At a pragmatic
6
5
4
3
2
0
1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012
1
Figure 1 Number of publications referring to ‘The Iceberg’, 1963–2012 Source: http://apps.webofknowledge.com/CitationReport.do?product¼WOS&search_mode¼CitationReport&SID¼2DFD2DF EM6C@n2L@FmI&page¼1&cr_pqid¼6&viewType¼summary (14 February 2013, date last accessed)
Downloaded from http://ije.oxfordjournals.org/ by guest on June 15, 2015
those days in an office and laboratory building behind the London Hospital Medical College. Jerry taught me a great deal of epidemiology by engaging me in revision of data for a second edition of his wonderful little book Uses of Epidemiology.3 There was a table in the first edition on ‘Completing the clinical picture’— demonstrating variation of the observed numbers affected by particular conditions according to the method of observation and the stage of the disease at which observations are made. It occurred to me as a former general practitioner that the numbers in this table would have considerable dramatic impact if they were projected onto the population of an ‘average’ general practice. There is greatest interest in the submerged part of the iceberg—disease precursors, preclinical conditions and very early clinical stages, that if identified and appropriate interventions initiated, might nip in the bud an otherwise relentlessly progressive and ultimately lethal disease process. This has become an integral part of teaching in family medicine programmes and other front-line aspects of health care. In the 50 years since the paper was published, great progress has been made in many aspects of clinical medicine, notably screening tests, diagnostic imaging, genomics and methods of detecting and managing inborn errors of metabolism. We can map the genome of apparently healthy people who will eventually develop Huntington’s disease, and girls and women at unusually high risk of developing aggressive breast cancer. Challenging philosophical and ethical problems have arisen since the health care system became capable of detecting precursors and early stages of these and other dangerous and often fatal conditions.4 The concept has been applied to examine the natural history of many conditions and suggest early diagnostic interventions. Consider depression and dementia. Incipient forms may be poorly defined
LAST AND ICEBERGS – SPOTTING THE ICEBERG DOESN’T PREDICT ITS SCALE
identified the concept ever since: ‘The iceberg’. We are all in his debt for this: my title was cumbersome and forgettable, whereas the vivid metaphor of the iceberg has proved to be memorable and appropriate.
Acknowledgement I am grateful to Natalia Abraham, Karen Trollope Kumar, Ian McDowell and Bob Spasoff for help with this paper. Conflict of interest: None declared.
References 1
2
3 4
5
Last JM. The Iceberg: ‘Completing the clinical picture’ in general practice. Lancet 1963;2:28–31. Reprinted Int J Epidemiol 2013; doi:10.1093/ije/dyt113. Web of Knowledge. Science Citation Index data, available at http://apps.webofknowledge.com/CitationReport.do? product¼WOS&search_mode¼CitationReport&SID¼ 2DFD2DFEM6C@n2L@FmI&page¼1&cr_pqid¼6& viewType¼summary (24 June 2013, date last accessed). Morris JN. Uses of Epidemiology. Edinburgh and London: E & S Livingstone, 1957. European Society of Human Genetics. Population genetic screening programmes: technical, social and ethical issues. Recommendations. Eur J Hum Genet 2003; 11(Suppl 2):S5–S7. See http://www.mayoclinic.com/health/dementia/DS01131 /DSECTION¼tests-and-diagnosis (14 February 2013, date last accessed) for description and critique of diagnostic methods for identifying dementia.
Published by Oxford University Press on behalf of the International Epidemiological Association ß The Author 2013; all rights reserved.
International Journal of Epidemiology 2013;42:1615–1617 doi:10.1093/ije/dyt123
Commentary: Last and Icebergs – spotting the iceberg doesn’t predict its scale, even after 50 years FD Richard Hobbs Department of Primary Care Health Sciences, New Radcliffe House, Walton Road, Oxford University, Oxford, UK. E-mail: [email protected]
Accepted
13 February 2013
Estimating the total disposition and magnitude of one’s adversaries compared with to what is readily
visible is a standard military prerequisite for tactics, which bears scrutiny as an option for delivering
Downloaded from http://ije.oxfordjournals.org/ by guest on June 15, 2015
level, I don’t think it matters much. It’s the concept that matters, not precise numbers of specified conditions. Another perspective on the ‘iceberg’ concept arose in discussions at community clinics and prepaid health care programmes. Administrators and managers suggested that the numbers of ‘expected’ cases of certain conditions could be compared with the numbers observed over a period of years, thereby providing a measuring instrument to evaluate the efficacy of screening procedures and routine clinical examination of patients. Although this might be possible, I would be cautious about suggesting use of the numbers from a theoretical model in any practical setting. Even the numbers from a large database such as the population of a prepaid health care plan covering many millions, as in California and the New England states, are subject to selection bias and random variation. I doubt whether valid conclusions could be based on comparison of 1 year’s experience in such a population with another, or comparison of clinic populations in different countries or regions. Such comparisons would be interesting, and some useful inferences might be derived from them but not to evaluate the efficacy of screening procedures or clinical care. After Jerry Morris had reviewed and approved my final text without suggesting any further changes, I sent it to Sir Theodore (‘Robbie’) Fox, the eminent editor of the Lancet. He accepted it without changing the text in any way, but did make one important modification. My title was ‘Completing the clinical picture in general practice’. Robbie Fox made that a subtitle and added as the title the word that has
1615
