Common cause and special cause (statistics)

Okay, imagine you're playing a game where you're trying to shoot a basketball through a hoop. There are two types of things that can affect how often you make the shot: things that always affect your shooting ability and things that only sometimes affect your shooting ability.


The things that always affect your shooting ability are called "common causes." Imagine you're playing the game indoors and there is a lot of noise coming from the hallway outside. The noise might distract you and make you miss the shot. This distraction would affect every shot you take - it's a common cause.


The things that only sometimes affect your shooting ability are called "special causes." Maybe you're feeling unusually tired or hungry during one round of the game, and you keep missing shots. This is a special cause because it only affects your shooting ability during that specific round of the game. Maybe you also eat a big snack before the next round and suddenly you're making all your shots again.


Common causes are things that affect a process all the time, while special causes are things that affect a process occasionally. In statistics, people analyze data to try and figure out if there are any patterns caused by common or special causes. Understanding these different causes can help find ways to improve processes and make them more predictable over time.