An iceberg is a useful metaphor. It appears most commonly as the tip of the iceberg, and it is a warning. Nine-tenths of an iceberg is under water, usually extending well beyond the area of the visible tip. Before radar, they were a terrible shipping hazard. The proper use of the metaphor, therefore, is as a warning that something much larger is out there.
Searching tip of the iceberg in PubMed® retrieves about 700. The first, from 1970, is a good example of correct usage. In Gonorrhoea and the iceberg phenomenon, the author discusses the problem of knowing the true incidence of gonorrhoea when it was reckoned that only one in five cases was reported. This is a frequent use, applied in recent years to HIV infection, Alzheimer’s disease, and cases of the Zika virus. It has also been applied more generally, for example, warning that highly selected groups in clinical studies seriously misrepresent the population.
By its second use in PubMed, only a few years later, it has already mutated to mean just the first signs of something larger, no ill implied. Discussing changes in informed consent, the author wrote, “only the tip of an iceberg of social change”. This is a poor use of the metaphor, unless the author was implying that the social change was a bad thing, which he wasn’t. Similar misuse includes an “expanding repertoire of targets for immune inhibition in bladder cancer” (where repertoire is also an unnecessary metaphor for number), psychiatric events being the first sign of multiple sclerosis, and the discovery that leucocytosis and neutrophilia as prognostic factors in anal cancer could identify the patients who need more treatment. If describing the first indication of a useful development, the tip of the iceberg is completely wrong but, unfortunately, now well established.
There are plenty of articles in PubMed about real icebergs, and you would be surprised how many there are about iceberg lettuce, a prime source of Escherichia, Salmonella, Cyclospora, and a number of other unwanted components of salad. The metaphor also appears in PubMed as “peak of the iceberg”. On Google, tip gets nearly 9 million hits, but peak only 170000. Peak, meaning the very top, is not the right word; the tip is everything from the surface of the sea to the peak.
Neville Goodman is a retired consultant anaesthetist and a writer. He is co-author of a book on medical English.
Competing interests: I have read and understood BMJ policy on declaration of interests and declare that my only competing interest is my co-authorship of a book about medical English.