THE ICEBERG REVISITED
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References
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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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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
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INTERNATIONAL JOURNAL OF EPIDEMIOLOGY
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
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
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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)
LAST AND ICEBERGS – SPOTTING THE ICEBERG DOESN’T PREDICT ITS SCALE
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
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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
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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