What is a correlation?
Correlation is a measure of the cause and effect between any two variables.
We hear statements like
There was traffic jam because of the heavy rains.
He got better marks because he had prepared well.
The higher the price, the lesser the demand.
In all these situations, we are discussing the effect of one variable on the other. If this effect can be measured in terms of numbers, it helps us in comparison.
The numerical measure of this effect of one variable on the other is called the correlation coefficient.
When there is no cause and effect in a relationship, the correlation coefficient is 0.