Definition
Correlation is a statistical measure that quantifies the strength and direction of the linear relationship between two variables. The most common measure is the Pearson correlation coefficient (r), which ranges from -1 to +1.
How to Interpret Correlation
The sign tells you direction. The magnitude tells you strength.
A school tracks study hours and test scores for 200 students.
r = 0.82 - a strong positive correlation.
As study hours increase, test scores tend to increase as well. But correlation does not prove that studying caused the higher scores - motivated students might both study more and perform better for other reasons.
Why It Matters
Correlation helps you identify relationships in data. Businesses use it to find which marketing channels are associated with sales. Doctors use it to identify risk factors for disease. Scientists use it as a first step before deeper analysis like regression.
The most important rule: correlation does not imply causation. Two variables can move together without one causing the other. Always look for confounding variables and consider whether the relationship makes logical sense.
Correlation measures how two variables move together. Always remember: a strong correlation does not prove that one variable causes changes in the other.