What does correlation mean?
Correlation refers to a mutual relationship or connection between two or more things — when one changes, the other tends to change as well. It is a cornerstone term in statistics, where it measures how closely two variables move together, expressed numerically as a coefficient ranging from -1 (a perfect inverse relationship) to +1 (a perfect direct relationship). Beyond mathematics, the word appears throughout science, economics, and everyday journalism to describe observed associations: researchers speak of correlations between diet and health, income and education, or sleep and memory. Crucially, correlation signals co-occurrence rather than cause; two things can rise and fall together by coincidence or through the influence of a third factor, a distinction captured in the famous maxim 'correlation does not imply causation.' Precise and versatile, the word lends analytical authority to writing about relationships between phenomena.
nounA mutual relationship or connection between two or more things, especially one in which a change in one is associated with a change in the other. In statistics, the degree to which two variables vary together, measured on a scale typically from -1 to +1.
- A mutual relationship or connection between two or more things.
- In statistics, the degree to which two or more variables move together, expressed as a coefficient.
"Researchers found a strong correlation between regular exercise and improved sleep quality."
"There is a well-documented correlation between smoking and lung cancer."
"The statistician calculated a correlation coefficient of 0.87 between hours studied and exam scores."
Regular plural, used when referring to multiple distinct correlations between different sets of variables.
"The study reported several significant correlations across age groups."
Correlation does not imply causation — ice cream sales and drownings rise together every summer, but neither causes the other; hot weather drives both.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of correlation
Correlation derives from the medieval Latin 'correlatio', formed from the prefix 'com-' (meaning 'together') combined with 'relatio' ('a carrying back' or 'relation'), itself from 'referre', 'to bring back'. The word entered English in the 16th century, initially in philosophical contexts describing reciprocal relations between concepts before extending into scientific and statistical usage in the 19th century. Its Latin root 'ferre' also gives English words like relate, relative, and correlate, all sharing the core idea of bearing or carrying something back in reference to something else.
Related word forms
How correlation is actually used
Correlation is a formal word, most at home in academic, scientific, and journalistic writing. In everyday speech, 'link', 'connection', or 'relationship' often serve instead. The phrase 'correlation does not imply causation' is a staple of scientific literacy discussions.
Easily confused with correlation
Correlation describes two things varying together, while causation means one actually produces or brings about the other — correlated events are not necessarily causally linked.