A fair experiment

You want to know whether plants grow better with music. You put one plant in the sun with music and one in the cupboard without. The one in the sun grows best — but was it the music or the sun?

A fair experiment changes only one thing. Everything else the same: the same soil, the same light, the same water. Only the music differs.

The thing you change is called the variable. The thing you measure is called the result. Everything held the same is the control.

Is it fair?

1. Two paper aeroplanes, different paper, the same folds, the same throw. → Fair (only the paper differs).
2. Two paper aeroplanes, different paper, one thrown by Lisa and the other by Ali. → Unfair (two things differ: the paper and the thrower).
3. Testing which ball bounces highest, dropping them from different heights. → Unfair.

The AI version: test two AI tools with the same questions and the same answer key, otherwise you do not know which one was better.