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link 14.01.2010 17:10 |
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Subject: fractional polynomial math. Regression models based on fractional polynomials (FP) functions of a continuous covariate are described by Royston and Altman (1994).*** Fractional polynomials were introduced by Royston and Altman (1994) as an extension of the familiar and well-established polynomial method of modelling with continuous predictors. The aim was to increase the range of functions that could be represented, while maintaining simplicity and mathematical tractability. We will denote by x a continuous prognostic factor. By transforming x, the first-order polynomial (i.e. linear function) y = a + bx is extended to the first-order fractional polynomial or FP1 function y = a + bx^p Заранее спасибо! |
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