Correlation

In statistics, if the values of one variable move in relationship with the values of the other variable, then the two variables are said to have a correlation. 

Consider the scatter plot of ice cream sales as a function of the temperature, which shows a distinct linear pattern. 

Since ice cream sales increase with temperature, these variables have a positive correlation.

Now, consider the scatter plot of hot chocolate sales as a function of temperature. The data points in this case also have a linear pattern and hence have a correlation.

But, hot chocolate sales decrease with the rise in temperature, so the variables have a negative correlation.

Apart from linear, other patterns can also be observed in real life. For example, as time passes, there is an exponential rise in the COVID cases before reaching a plateau. So this is a non-linear, positive correlation.

There can be cases where there is no correlation between the two variables. For example, the number of movies watched has no correlation with shoe size.