Axa Rosenberg's model involves thousands of multivariate regression calculations, but it all boils down to the same thing that old-fashioned value investors are looking for: an estimate of fair value, which is then compared with current stock prices.

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Important cases where the computational definition of R2 can yield negative values, depending on the definition used, arise where the predictions which are being compared to the corresponding outcomes have not been derived from a model-fitting procedure using those data, and where linear regression is conducted without including an intercept.

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Using such intervals communicates the uncertainty within the model introduced by the scatter of the data instead of using the regression line that makes the relationship appear far more deterministic than it really is.

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