statistics
posted by Rebecca .
Please Help! My book and instructor are no help. Please help me understand why I need to make a scatter diagram, when dealing with bivariate data, and how to find SS(x), SS(y), SS(xy), and r. I have all the formulas, but don't understand. Thanks!
I don't know that the diagram is required to be drawn, if you have all the xi, yi.
See http://www.ms.unimelb.edu.au/~s620202/EMS05ch7.pdf
Using Excel, there is a method of doing the scatter plot, then a fitted line, and from that, determining SS.
So, I really guess I cant offer much help....is there another student in your class you can team up with...that is my recommendation.
Why a scatter diagram?
Well, to repeat a phrase, a picture is worth a 1000 words. With a scatter diagram, one can usually see, at an instant, any correlation between the variables x and y.
SS(x), SS(y), and SS(xy) are, by themselves, not very interesting or informative. However, they are components of calculations that are very helpful. So, dividing SS(x) by n1 gives the sample variance of the x value; a very helpful statistic.
Combining the three statistics, according to your formula, gives r, which is a correlation statistic. r provides a measure of the linear relationship (correlation) between x and y. With a high degree of correlation, one can use values of x to predict values of y  Which is what regression analyses is all about.
I hope this helps.
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