Correlation refers to the linear relationship among the variables. For example, the blood pressure of a patient may be correlated with age, food habits and family history and so on. If we study the degree of relationship among the above variables, it is known as correlation.

Correlation Analysis enable us in determining the degree and direction of relationship between two variables.

If change in value of one variable changes the value of another variable then we say that there is correlation between two variables . if price (x) of a commodity changes then the quantity of demand (y)also changes . So, there is a correlation between the price and demand.

The measure of correlation provides the degree of correlation between the variables.

## On the basis of number of variables studied at the time the correlation can be categorized into following three different categories:

## 1. Simple correlation:

When we study only two variables at a time then a correlation is called simple correlation.

## 2. Multiple correlation:

When we study three or more variables at a time then we say that a correlation is multiple correlation.

## 3. Partial correlation:

When among the three variables the value of 1 variable is kept fixed or constant and study the correlation between other two variables then it is called partial correlation.