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BookAnother de ning moment for epidemiologyMany epidemiologists are obsessed with definitions. A 1978 paper entitled De nitions of epidemiology presented 26 of them, documenting how the subject had evolved from an original focus upon epidemics, to infections in populations, and on to broader concerns with all disease in populations. This enthusiasm has continued, culminating for the moment in the sixth edition of the International Epidemiology Associations A Dictionary of Epidemiology, which de nes its subject thus: The study of the occurrence and distribution of health-related events, states, and processes in specified populations, including the study of the determinants influencing such processes, and the application of this knowledge to control relevant health problems. Many will nd this de nition awkwardbut let us also note that its emphasis is now upon health.

One may ask why this obsession with definitions, and why this evolution. The obsession derives from the methodological nature of epidemiologyit is about methods for studying things in populations, often under complex circumstances, and quite rightly concerns itself with proper tools of inference and the various pitfalls and biases that may lead to inappropriate conclusions. Epidemiologists are fussy people, by nature and trainingany good epidemiology course hammers the importance of explicit and detailed de nitions of cases and of comparison groups, of detailed validation of variables, and of appropriate statistical measures. The evolution re ects another aspect of the subject: that the methods are applicable to many disciplines which deal with populations, and not just those which deal with epidemics or disease. Indeed, given the prominence of health in the latest definition of epidemiology, and the fact that health is itself de ned (following WHOs lead) as a state of complete physical, mental,

and social well-being and not merely the absence of disease or infirmity, epidemiologys territory now extends, by definition, to studies of social wellbeingwhich is very broad indeed.

This breadth is important. Although the word epidemiology is etymologically non-specific (meaning just studies upon the population), it is no accident that the subject evolved primarily with emphasis on human disease. The importance of illness for all human societies was an obvious stimulus. The early work of James Lind on scurvy, Percivall Pott on scrotal carcinoma, Daniel Bernoulli on smallpox, William Farr on mortality

statistics, Peter Panum on measles, and John Snow on cholera, among many others, led to the establishment of epidemiology as a professional and academic discipline in the late 19th and early 20th centuries, and to substantial support for epidemiological research from governments and other sources in the past century. Notwithstanding this historical emphasis, many authors have noted the applicability of epidemiological methods beyond human disease. For example, the Epidemiological Society of London, the first organisation devoted to the subject, set up a committee in the 1850s to inquire into the diseases affecting the Vegetable Kingdom. And Ronald Ross, Nobel Laureate for his work on malaria, commented in a classic epidemiological text in 1911: We shall deal with time-to-time variations not only of malaria, but of all disease, and not only of diseases of man, but those of any living organisms. Still further, as infection is only one of many kinds of events which may happen

to such organisms, we shall deal with happenings in general.

Although this broad reach is touched upon in its preface, A Dictionary of Epidemiology shies away from embracing its full constituency, and focuses almost entirely upon traditional medical and disease-related language, and human populations. In fact, virtually all the tools of epidemiology are now used, and often explicitly called epidemiology, in other elds related to social wellbeing, notably criminology, education, and economics. As just one example, randomised controlled clinical trial methods are increasingly used in these and other social science elds. As these non-medical fields mature, it is likely that several of their special methods derived in non-medical contexts will assist medical research. After all, Gregor Mendel worked on peas, and much of biostatistics started with agriculture. That said, the broadening scope of epidemiology poses an interesting challenge for textbooks, courses, journals, and professional organisations that purport to represent the discipline of epidemiology per se.

There are some unfortunate lapses in this new edition. Readers searching clari cation on infectious diseases will be shocked to nd that infectious agent has been de ned as A non-eukaryotic microscopic element, which would imply that protozoaagents of malaria, sleeping sickness, and amoebic dysentery, among other diseaseswere not infectious agents. And if readers attempt to cross-reference around the subject they will be bemused to be told that colonisation is a synonym for infection and that All infectionsare communicable diseases. Curiously, the word infect is not de ned.

Even more important is what this edition has done to one of the most fundamental terms in epidemiology: risk factor. The previous editions all de ned a risk factor as something that

A Dictionary of Epidemiology Sixth EditionEdited for the International Epidemiology Association by Miquel Porta. Oxford University Press, 2014.Pp 376. US$3500ISBN 9780199976737epidemiologys territory now

extends, by de nition, to studies of social wellbeingwhich is very broad indeed

Further reading

Lillienfeld DE. De nitions of epidemiology. Am J Epidemiol 1978; 107: 8790

Lind J. A treatise of the scurvy. In three parts. Containing an inquiry into the nature, causes and cure, of that disease. Together with a critical and chronological view of what has been published on the subject. Edinburgh: Sands, Murray and Cochran for A Kincaid and A Donaldson, 1753

Waldron HA. A brief history of scrotal cancer. Br J Ind Med 1983; 40: 390401

Bernoulli D. Essai dune nouvelle analyse de la mortalite causee par la petite verole. Paris. Mem Math Phys Acad Roy Sci 1766

Langmuir AD. William Farr: founder of modern concepts of surveillance. Int J Epidemiol 1976; 5: 1318

Panum PL. Observations made during the epidemic of measles on the Faroe Islands in the year 1846, trans Hatcher AS. New York: FH Newton, 1940

Snow J. On the mode of communication of cholera. Second edition. London: John Churchill, 1855

Transactions of the Epidemiological Society of London for the year 1855. London: T Richards, 1856

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Ross R. The prevention of malaria. Second edition with an

addendum on the theory of happenings. London:

John Murray, 1911

Fine PEM, Goldacre BM, Haines A. Epidemiologya science for the

people. Lancet 2013; 381: 124952

Hill AB. The environment and disease: association or

causation? Proc R Soc Med 1965; 58: 295300

In briefa cholera-belt (1882) supposed to protect against bowel complaints and miasma, to a Design for double spectacles (1846), o ering an extra lens hinged to either side of the usual lenses, which claimed to be suitable for both close-up and distance viewing. The rst of these devices is simply a lancet attached to one end of an india-rubber cylinder containing an adjustable piston. According to the inventors spec, On releasing the instrument from the pressure of the fingers, the tendency of the elastic cylinder to expand and resume its original form produces a sucking action which continues until it is lled more or less with blood. Arti cial leeches had a potential market, Halls alarmingly notes in her introduction, because of a shortage of natural leeches due to overuse by doctors and patients treating everything from headaches to prostate problems with bloodletting.

Would any of the books devices have made the reputation and fortune of their designers, had they been constructed? One has grave doubts, with the possible exception (I hazard) of the Combined walking stick and railway-carriage door-key. Instead, these inventions provide entertaining glimpses of the lives, hopes, and fears of our 19th-century forebears.

Andrew Robinson

Book Ingenious inventions During the 19th century a handful of British inventions changed the world, notably railways, electric motors, and chloroform anaesthesia. Some inventions were less revolutionary but remain vital today, such as macadamisation in road-building and the safety bicycle. Yet others worked well for a while, like the Brougham horse-drawn carriage, before becoming redundant with advancing technology. Most inventions never left the drawing board, however. After being registered by their optimistic inventors, they were consigned to the vaults of the UK Governments designs registry at Somerset House in London, and utterly forgotten. Now, Julie Halls has exhumed a selection of the coloured drawings and copperplate descriptions from the volumes where they were originally pasted, and created an irresistible illustrated book Inventions That Didnt Change the World.

In the 19th century anyone who had an idea that might solve a problem or speed up a task could come up with a technical solution, writes Halls, a National Archives specialist in these registered designs, who regards them with a combination of respect and mirth. Inventors were ingenious, imaginative, sometimes misguided, but, in the unexpected world of Victorian inventions, ever

hopeful. Some were professionally quali ed, such as a surgeon o ering a Design for an improved pneumatic inhaler; many more seem to have been industrious amateurs.

The inventors were responding to the intro duction of the Designs Registration Act in 1839, and sub-sequent copyright legislation leading up to the Great Exhibition of 1851. Hitherto, the only way to protect an invention was to take out a patent. However, the patent system was extremely cumb ersome and expensive. The idea behind the new act was to reserve the patent system for important inventions, rather than snu ers, stirrups, lamps, cork-screws, and other articles of domestic use, in the words of a parliamentary select committee on patents. The latter items were to be treated as a new shape or con guration of an already existing useful object, and protected by registration for 3 years for a fee of 10.

Hallss book contains mainly designs for domestic articles and is divided into chapters on House and Garden, Field and Factory, His and Hers, Out and About, Preventatives and Panaceas, Sport and Leisure, and Safety and Security, each introduced by some informative social history.The medical devices in Preven tatives and Panaceas range from Arti cial leeches (1848) and a Design for

is associated with risk; but suddenly we nd, in this edition: Risk factor (Syn: determinant) A factor that is causally related to a change in risk of a relevant health process, outcome, or condition. Although we all know that association need not imply causation, this new de nition is presented with no signal or acknowledgment of the change. Given the importance, and complexity, of unravelling causal versus non-causal relations in much epidemiological work, this bold shift is bound to disturb many people. The

inevitable confusion will not be helped by a nal sentence in the text which follows the definition of risk factor: To prevent medicalization of life and iatrogenesis, the relevance and significance of the factor-outcome risk relationship must be cautiously assessed; so must uncertainties and ambiguities in risk-related concepts, as well as di erent legitimate meanings of risk across and within cultures. This is not an easy sentence, but would seem more consistent with the traditional definition of a risk

factor than with the sixth editions radical departure.

Let us hope that the editors of the next edition will be encouraged: to accept the challenge of the subjects breadth; to strive for correct, consistent, clear, and concise de nitions; and maybe even to start by de ning epidemiology once again, quite simply and appropriately, as studies upon the population.

Paul Finepaul. ne@lshtm.ac.uk

Inventions That Didnt Change the WorldJulie Halls.

Thames & Hudson, 2014. Pp 224. 1995

ISBN 9780500517628

Andrew Robinson is the author of The Last Man Who Knew Everything,

a biography of physician and polymath Thomas Young.