Guess the correlation
Ten scatter plots. Call r by eye. Within 0.10 keeps your streak alive.
- Round
- 1/10
- Streak
- 0
- Best avg miss
- –
0.00
−1 perfect down0 none+1 perfect up
What’s going on
r measures how tightly points hug a straight line, from −1 to +1. The sign gives the direction. The size gives the tightness, not the steepness: a shallow line through a tight cloud can have a bigger r than a steep line through a loose one.
r = Σ(x − x̄)(y − ȳ) / √[Σ(x − x̄)² · Σ(y − ȳ)²]
Square it and you get r², the share of the spread in y that the line explains. An r of 0.5 explains only 25%, which is why a moderate correlation looks so messy.
Each plot has 60 points. You are scored against the r of those exact 60 points, not the setting used to draw them. After each call, the least-squares line appears so you can see what you were judging.