For one of the early lectures of our parasitology course, our professor set out to discuss something that he called one of the most profound and useful concepts in epidemiology: Arnold. He wrote it large on the blackboard as R0 (spoken as r-naught) but his British accent turned it unerringly into plain Arnold.
I began to think of Arnold as a quiet, middle-aged individual, wandering around oblivious to the hordes of scientists swarming like paparazzi. We estimated Arnold, more concerned with his general ratio than any particular measurements. We discussed what would happen if Arnold was greater than one (the disease spreads through a host population) or less than one (the disease dies out), and I pictured Arnold sitting down in his living room, going through his baby photos, while that gaggle of scientists peered in through the windows. We took notes on Arnold’s personal preferences, discussing how Arnold could be impacted by environmental factors such as temperature. We even wrote down equations to take a closer look at Arnold, not leaving him much privacy at all. Eventually the lecture moved on to particular disease traits and population growth curves, but underlying everything we discussed was this profound idea of the basic concept of Arnold.