In order to communicate without misunderstandings, it is important to realise that in contrast to spoken language, a combination of words; gestures; facial expressions; and with possibilities for immediate questioning and correcting, written language relies entirely on usage of the right words and compliance with the grammatical rules for combining these into understandable sentences at the time of writing. Furthermore, scientific communication is based on the tenet that author and reader have identical definitions of the used words. Otherwise, confusion can be expected.

Statistical terminology is well defined. The terms are described in statistical dictionaries, the most well-known probably being published by The International Statistical Institute (The Oxford Dictionary of Statistical Terms. Oxford University Press, New York 2003). However, statistical terminology is systematically misused in medical research. A sort of pigeon terminology has arisen. For example, terms such as range, quartile, and correlation, are almost always used incorrectly. The range is not the smallest and greatest values but the difference between these. A quartile is one of the three, not four, values (Q1, Q2, Q3) that divide the ordered observations into four parts with equal size (Q2 is also the median). A correlation is not a general association but a measure of the strength of the statistical relationship between two variables. When used incorrectly, the terminology needs to be corrected.

Other terms, such as primary endpoint, adverse event, and intention to treat, play important roles in randomised trials, but are increasingly often used in observational studies where their meaning is unclear. The primary endpoint is part of a strategy for addressing multiplicity issues in confirmatory trials but observational studies are not confirmatory. Adverse events refer to any untoward medical occurrence in a patient. The event does not necessarily have to have a causal relationship with the studies treatment, and such information is usually not collected in an observational study. Intention to treat refers to a feature of the study design that cannot be achieved in an observational study. The use of these trial-related terms in manuscripts presenting observational studies is thus obscure. An explanation of how the terms should be interpreted and a motivation for their use is needed. The ICMJE recommendation is to “Avoid nontechnical uses of technical terms in statistics”.

Correcting the terminology is not generally popular among physicians, but it is an important part of a statistical review.

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