Statistics · Data presentation
Chapter 1 · 3
The idea
Measuring correlation (the PMCC)
The product moment correlation coefficient r as a number between −1 and 1 measuring linear correlation — computing it from the summary statistics S_xy, S_xx, S_yy, interpreting it in context, and why coding leaves it unchanged.
A full journey — read it, play with it, work it, then earn real exam marks. Everything stays on the timeline below.
In this lesson — start anywhere
Statistics · Data presentation
Measuring correlation (the PMCC)
The product moment correlation coefficient r as a number between −1 and 1 measuring linear correlation — computing it from the summary statistics S_xy, S_xx, S_yy, interpreting it in context, and why coding leaves it unchanged.
Why it works
A number for the cloud
A scatter diagram lets you describe correlation — positive or negative, strong or weak — but the product moment correlation coefficient (PMCC), written , puts a number on it. It always lies in where is perfect positive linear correlation (all points exactly on a rising line), is perfect negative, and is no linear correlation at all. The closer is to , the tighter the cloud hugs a straight line.Keep reading — free
The rest of the explanation, plus 3 worked examples you step through move by move.
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