Document ID: DQ073 Relevant to following products: WorkOut 2.0 Manta Document description: What is R²?

R² is one way of measuring the goodness of the fit.

Note, although the small 2 looks like it is the square of R it does not actually mean that.

R² does not have any units and is a fraction between 0 and 1, the higher the number the better the fit. You can consider that R² compares the fit with a horizontal line, if the result is 0 then the fit is no better than a horizontal line through the mean of the Y values. If R² is 1 then all points lie exactly on the fit (i.e you can calculate Y exactly from the fit). Also, R² may even be negative if the fit is really bad – again you would not expect this for something squared.

R² is calculated as: 1 minus the ratio of SS / (the sum of the squares of the differences between Y fit and the mean Y value).