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Best Fit Lines & Curves by Alan R. Jones

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5 Linear transformation: Making bent lines straight

A straight line is just a curve that never bends!

Estimating would be so much more straightforward if our estimating or forecasting technique was, well, straight forward . . . or backward, i.e. just a question of projecting values along a straight line. That way we only need to concern ourselves with one input variable and two constants (an intercept and a slope or gradient) in order to get an output variable:

Output = slope × Input + Intercept

Unfortunately, in reality many estimating relationships are not linear. However, there are some instances (especially where we need to interpolate rather than extrapolate) a linear approximation may be adequate for the purposes of estimating. As George ...

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