Correlation is a relationship between two things that tend to change together in a predictable pattern. When scientists notice that taller students usually have bigger feet, they're observing a correlation: as one measurement increases, the other tends to increase too.

Correlations can work in different directions. Height and shoe size show a positive correlation because they rise together. Screen time before bed and sleep quality show a negative correlation: as one goes up, the other typically goes down. When your teacher notices that students who read more tend to score higher on vocabulary tests, she's spotting a correlation.

Here's the crucial thing about correlation: just because two things correlate doesn't mean one causes the other. Ice cream sales and drowning incidents both increase in summer, showing a strong correlation, but ice cream doesn't cause drowning. The real cause is warm weather, which leads to both more swimming and more ice cream eating. Scientists call this principle “correlation does not imply causation.”

Recognizing correlations helps us spot patterns and make predictions, but understanding what actually causes what requires deeper investigation. When you notice that your basketball shooting percentage correlates with how much you practice, you're probably right that practice causes improvement. But if you notice your lucky socks correlate with winning games, you might want to look for other explanations first.