Neville Goodman’s metaphor watch: The whole spectrum

neville_goodmanSpectrum originally meant the same as spectre: a ghost. It was appropriated by Newton in 1671 to describe how sunlight passing through a prism “exhibited… a Spectrum of divers colours” (OED). The modern definition is “The entire range of wavelengths (or frequencies) of electromagnetic radiation [or] any one part of this larger range” (OED). Among the figurative uses (The entire range or extent of something, arranged by degree, quality, etc.) cited by the OED is one from medicine, from 1964: “Theoretically, students remain long enough on each type of ward to give them a spectrum of experience.”

To which I have to say: what is wrong with range or variety? The point about spectrum is that it is continuous. Although we talk of the seven colours of the rainbow, they merge into one another: there are no discrete boundaries. To take the example of lung disease: lung cancer, idiopathic pulmonary fibrosis, and lobar pneumonia form a range or variety of diseases, but in no way are they a spectrum. Lung cancer doesn’t merge seamlessly with lobar pneumonia (although they may co-exist). The pathological processes underlying these diseases are discrete.

Spectrum makes sense for the lymphoproliferative disorders, where pathology does merge, and for many psychiatric conditions, where pathology is a mystery but presentation is protean. Autistic spectrum accounted for 14% of all occurrences of spectrum in PubMed® in 2016, an 18-fold increase since 2000; but spectrum, unlike option or strategy, isn’t a vogue word: its overall prevalence in PubMed altered little over that time.

Broad spectrum antibiotic is well accepted: it is a term of US origin, although the first use that I could find in PubMed was an article in the South African Medical Journal (in 1952) about Ilotycin [erythromycin], described as “a new broad-spectrum antibiotic” [my italics], so I presume the term was already extant.

Spectrum is wrong describing “a spectrum of retinal vessel measures”, which were a number of discrete and different techniques; “a broader spectrum of patients… undergoing coronary artery bypass grafting”, which was a wider range; “elevated systolic blood pressure across its usual spectrum”, which is hypertension of whatever level; “whether the benefit… was observed across the spectrum of HF risk”, where the unnecessary abbreviation is heart failure, and the spectrum is all patients; and “a unique and distinct spectrum of adverse events”, which is an unspeakable horror.

Another word sometimes used instead of range is gamut. Originally a term from music, it came to mean “the whole scale, range, or compass of a thing” (OED). Thus the whole gamut is unnecessary.

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.