On the Statistical Measure of Infectiousness

TLDR

Diseases differ in how readily they spread, with measles, mumps, whooping‑cough, scarlet fever, diphtheria, common cold, influenza, and gonorrhoea illustrating a spectrum from highly contagious to less so. The study seeks to uncover the factors that shape perceptions of how contagious various illnesses are.

Abstract

We all recognise that some diseases are more “catching” than others. Every mother knows that measles is very catching and most people set aside a group of common complaints, measles, mumps, whooping-cough, scarlet fever, diphtheria—perhaps roughly in that order—as catching complaints. Then again, still keeping ourselves within the circle of ideas of educated non-medical people, one has such complaints as common colds or influenza which one thinks of as running through a house indeed but does not put quite into the measles category, as one feels that factors determine the spread other than mere proximity to a sick person. Lastly, one has some illnesses, gonorrhoea would be a fair example, which everybody recognises to be spread wholly by contagion, almost always by a particular method of contagion, but does not regard as catching at all in the sense that measles and whooping-cough are catching. When we enquire into the reasons of these opinions they will be found, I think, to be these.