Muggle Interlude: Compartments
D’s scroll described what scientists call 3 “compartments”. A compartment simply means a group of organisms that is defined by some distinct characteristic. In ordinary life we classify people in many ways:
- Students, teachers, or administrators
- Americans, Germans, Lithuanians…,
- Children, adult, senior
In fact any time you say “the world is divided into 2 kinds of people…” you are compartmentalizing. The important thing is that people (or other organisms) fit into one and only one compartment at a given time. They can (often) move between compartments, but they can’t belong to more than one at a time.
In scientific or medical models, compartments are used extensively. A scientist thinking about disease might choose to compartmentalize his subjects based on
- Age
- Gender
- Health history (i.e., smokers, non-smokers, reformed smokers)
But the most basic compartmentalization by far for studying disease is simply “are you, or have you ever been, sick with this disease?” This defines 3 compartments:
- S: People who have not been sick and are therefore Susceptible
- I: People who are now sick
- R: People who have been sick and are therefore not susceptible any more.
As we’ll see later, you can certainly get more involved than that, but right now we’re going for the simplest possible model.
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