I am writing a Maths Assignment for school in which I find a correlation between two sets of variables. The formula I am using for the gradient of the regression line is:
$$m=\dfrac{S_{XY}}{(S_X)^2}$$
Where
$$S_{XY}=\sum xy-\dfrac{\sum x\sum y}{n}$$ $$(S_X)^2=\sum x^2-\dfrac{(\sum x)^2}{n}$$
I am confused and cannot find any information online about the name or origin of the S variable. I need to include this into my report and it would be really helpful if anyone knows what it is!
Thank you :)