Epidemiology: Everything Turns on One Number Crossing One
If each case produces more than one further case, an outbreak grows; below one, it fades. That threshold is simple — and almost everything else about the subject is context-dependent.
Concept
The Law of Large Numbers
Behavioral Economics: The Errors Point the Same Way
If people departed randomly from rational choice, the departures would cancel out. They lean consistently in the same directions — which is what makes them worth studying, and worth worrying about.
Benford's Law: Why So Many Numbers Start With One
Around thirty per cent of numbers in real datasets begin with 1, and only five per cent with 9. People inventing figures don't reproduce that — which is how the pattern became an auditing tool.
The Central Limit Theorem: Why Bell Curves Are Everywhere
One die is flat. Ten dice added together make a bell curve. The shape is a property of adding independent things — which tells you exactly when to expect it and when not to.
The Law of Large Numbers: Small Samples Are Wild
Seven heads in ten flips is unremarkable; seventy thousand in a hundred thousand would be extraordinary. The same probability, different room for chance — with consequences most people miss.