What does correlation of data mean?

Answer 1

Correlation of data means that two different variables are linked in some way. This might be positive correlation, which means one goes up as the other goes up (for instance, people who are heavier tend to be taller) or negative correlation, which means one goes up as the other goes down (for instance, people who are older tend to play Video Games less often). Correlation just means a link. It means that knowing one variable (a person is really tall) is enough to make a guess at the other one (that person is probably also pretty heavy).

Note that there is a very common mistake people make about correlation, and this needs to be addressed. In short, the mistake is "correlation implies causation". It doesn't. If I have data which shows people who volunteer more often tend to be happier, I cannot then say "volunteer. It makes you happy!" because correlation doesn't imply causation - it might be that if you're happy you're more likely to volunteer, and the causation is the other way around. Or it might be that if you're rich, you're both more likely to be happy, and more likely to volunteer, so the data is affected by a different variable entirely.